Fabrication and Characterization of an FeBNdNb Magnetic Metallic Glass Thin Film

2012-05-08T09:00:00+09:00

Authors: Tuan Anh Phan, Sangmin Lee, Akihiro Makino, Hiroyuki Oguchi, Hiroshi Okamoto, and Hiroki Kuwano
We have fabricated an Fe_{67.46}B_{22.5}Nd_{6.3}Nb_{3.74} magnetic metallic glass thin film on a (100) silicon substrate by electron cyclotron resonance ion beam sputtering. We confirmed the metallic glass state of the thin film by observing its crystallographically amorphous state using X-ray diffractometry and transmission electron microscopy, and we obtained the glass transition temperature using differential scanning calorimetry. We also confirmed the magnetization of the thin film using a physical property measurement system. The thin film showed the largest reported width of the supercooled liquid region (96 K) and the smallest reported value of coercivity (7.5 A/m) among the existing magnetic metallic glass thin films. This study is expected to lead to an increase in the variety of materials available and greater knowledge of the physical properties of magnetic metallic glass thin films and to facilitate research on developing magnetic metallic glass thin films as base materials for magnetic microelectromechanical systems.

18-GHz, 4.0-aJ/bit Operation of Ultra-Low-Energy Rapid Single-Flux-Quantum Shift Registers

2012-05-07T09:00:00+09:00

Authors: Masamitsu Tanaka, Masato Ito, Atsushi Kitayama, Tomohito Kouketsu, and Akira Fujimaki
We demonstrate rapid single-flux-quantum (RSFQ) circuits with reduced energy consumption by lowering the driving voltages and critical currents of Josephson junctions (JJs). At lowered voltages, the energy statically consumed by bias resistors (which is dominant in RSFQ circuits) is reduced. In addition, we show that when RSFQ circuits are driven by lowered constant voltages, the dynamic energy consumption resulting from the switching of JJs is reduced because of the suppression of the amplitudes of the signal voltage pulses, even though the switching speed becomes slower. Utilization of miniaturized JJs with smaller critical currents also leads to the reduction of static and dynamic energy consumption without decreasing the switching speed. We have designed and tested ultra-low-energy 8-bit shift registers, and verified the correctness of high-speed operations up to 18 GHz. The average energy consumption, including that at the bias resistors, was measured at 4.0 aJ/bit, which represents an energy efficiency two orders of magnitude better than that of standard RSFQ circuits.

Comparison of Two Types of Recessed-Gate Normally-Off AlGaN/GaN Heterostructure Field Effect Transistors

2012-05-07T09:00:00+09:00

Authors: Zhiyuan He, Jialin Li, Yuhua Wen, Zhen Shen, Yao Yao, Fan Yang, Yiqiang Ni, Zhisheng Wu, Baijun Zhang, and Yang Liu
In this report, two types of normally-off AlGaN/GaN heterostructure field effect transistors (HFETs) with recessed-gate structure have been fabricated by using common technique of induced coupled plasma (ICP) dry etching and a novel technique of selective area growth (SAG), respectively. The devices fabricated by SAG (SAG-HFET) showed better performance than that of ICP-HFETs with larger maximum drain current of 300 mA/mm, positive threshold voltage of 0.4 V, and lower pinch off channel leakage current (2.17×10^{-3} mA/mm). The analysis indicates that such obvious difference originated from the different AlGaN quality of the gate region under the Schottky contact, in which the damage to the gate region stemmed from dry etching can be avoided by the SAG technique so that the forming of higher quality Schottky contact can be guaranteed. These results indicate that SAG technique is a promising method for fabricating the normally-off GaN based HFETs.

Ultrasensitive Far-Infrared Phototransistors Fabricated in Superlattice Structures

Takeji Ueda, Naomi Nagai, and Susumu Komiyama — 2012-05-02T09:00:00+09:00

Authors: Takeji Ueda, Naomi Nagai, and Susumu Komiyama
Charge sensitive infrared phototransistors (CSIPs), ultrasensitive detectors in the wavelength range of 10–50 µm, are fabricated in GaAs/AlGaAs superlattice structures. The superlattice structures consist of alternately grown 2-nm-thick Al_{0.3}Ga_{0.7}As tunnel barriers and thickness-modulated GaAs layers from 2 to 10 nm. The tilted miniband formed in a superlattice structure serves as a potential slope similar to formally used compositionally graded barriers. The utilization of the superlattice in a CSIP is expected to give advantages of easier design, less impurities, and better repeatability in crystal growth, and therefore provides more reliable device performance. The novel structure paves the way for the future mass production of CSIPs.

Quantum Transport Theory of Direct Current Conductivity in the Presence of Spin–Orbit Interaction

Nam Lyong Kang and Sang Don Choi — 2012-05-02T09:00:00+09:00

Authors: Nam Lyong Kang and Sang Don Choi
Utilizing the conductivity formula derived using the projection-reduction method, which combines a Kang–Choi (KC) reduction identity and a state-dependent projection operator in the linear response scheme, we investigate the effect of Rashba spin–orbit coupling on the direct current (dc) conductivity of a two-dimensional electron–phonon system when the perpendicular magnetic field is applied. A diagram representation of the formula is introduced, by which the validity of the theory is confirmed. We find that the dc conductivity oscillates with the inverse magnetic fields and the peak points of the oscillation appear near the reversion points of energy branches.

Ratchet Effect of Single Vortex Motion in Superconducting Asymmetrical Nanobridges

Kemmei Kajino, Keisuke Fujita, Baoyu An, Masumi Inoue, and Akira Fujimaki — 2012-05-02T09:00:00+09:00

Authors: Kemmei Kajino, Keisuke Fujita, Baoyu An, Masumi Inoue, and Akira Fujimaki
We have successfully obtained asymmetrical current–voltage (I–V) characteristics in YBa_{2}Cu_{3}O_{7-x} (YBCO) nanobridges patterned with asymmetrical geometry. These asymmetrical nanobridges (ANBs) are shown to control vortices one at a time. The critical current I_{c}, of 200-nm-wide and 100-nm-thick ANB changes by a maximum of 9% when a magnetic field of 2.4 mT is applied. The I_{c} variation ΔI_{c} increases monotonically with increased magnetic field from -2.2 to 2.4 mT. The asymmetrical I–V characteristics obtained in our experiment are due to the restriction of vortex motion by the asymmetrical surface barrier (the so-called vortex ratchet effect). The width and thickness dependencies of the I–V asymmetry are also studied, and indicate that the bias current and the Meissner screening current, determined by the relative width compared to the effective penetration depth of the YBCO film, dominates the I–V asymmetry characteristics.

Ultraviolet Photoresponse Properties of Single-Walled Carbon Nanotubes Decorated with Thickness-Controlled ZnO Layer by Pulsed Laser Deposition

2012-05-02T09:00:00+09:00

Authors: Kenta Itabashi, Hiroshi Tabata, Winadda Wongwiriyapan, Shinji Minami, Kazutoshi Matsushita, Ryotaro Shimazaki, Tsuyoshi Ueda, Tatsuya Ito, and Mitsuhiro Katayama
We fabricated single-walled carbon nanotubes (SWNTs) covered with a thickness-controlled ZnO layer (ZnO–SWNTs) by pulsed laser deposition (PLD) and investigated their UV photoresponse, induced by the photodesorption of oxygen molecules from the ZnO surface. The magnitude of the negative photocurrent and the recovery time were strongly dependent on the thickness and morphology of the ZnO layer, and were highest when the ZnO layer was 3–4 nm thick. The observed recovery curves of the negative photocurrent were fitted with double-exponential-function curves, which indicate the coexistence of two types of adsorption sites for oxygen molecules on the ZnO surface. The light intensity dependence of the negative photocurrent was also measured.

Control of In Surface Segregation and Inter-Diffusion in GaAs on InGaP Grown by Metal–Organic Vapor Phase Epitaxy

Yasuyuki Fukushima, Takayuki Nakano, Yoshiaki Nakano, and Yukihiro Shimogaki — 2012-05-02T09:00:00+09:00

Authors: Yasuyuki Fukushima, Takayuki Nakano, Yoshiaki Nakano, and Yukihiro Shimogaki
In order to fabricate abrupt heterointerfaces of the GaAs/InGaP system by metal–organic vapor phase epitaxy (MOVPE), we studied the In atom distribution by X-ray photoelectron spectroscopy (XPS). The systematic XPS depth profile analyses revealed that the InGaP surface contains an excess amount of In atoms owing to surface segregation. The excess In atoms diffuse into the GaAs layer and cause compositional mixing at the interface of GaAs on InGaP. In order to suppress the interdiffusion and surface segregation of In atoms into GaAs on InGaP, we have developed a novel gas switching sequence for growing GaAs on InGaP. That is, after the growth of InGaP, only tertiarybutylphosphine (TBP) was introduced, and after stopping the supply of TBP, trimethylgallium (TMGa) was pre-introduced to the reactor before the growth of GaAs. Then tertiarybutylarsine (TBAs) was allowed to flow to initiate GaAs growth. This novel gas switching sequence contributed to the formation of abrupt heterointerfaces of GaAs on InGaP.

Thermally Dried Ink-Jet Process for 6,13-Bis(triisopropylsilylethynyl)-Pentacene for High Mobility and High Uniformity on a Large Area Substrate

Gi Seong Ryu, Myung Won Lee, Seung Hyeon Jeong, and Chung Kun Song — 2012-05-01T09:00:00+09:00

Authors: Gi Seong Ryu, Myung Won Lee, Seung Hyeon Jeong, and Chung Kun Song
In this study we developed a simple ink-jet process for 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene), which is known as a high-mobility soluble organic semiconductor, to achieve relatively high-mobility and high-uniformity performance for large-area applications. We analyzed the behavior of fluorescent particles in droplets and applied the results to determining a method of controlling the behavior of TIPS-pentacene molecules. The grain morphology of TIPS-pentacene varied depending on the temperature applied to the droplets during drying. We were able to obtain large and uniform grains at 46 °C without any “coffee stain”. The process was applied to a large-size organic thin-film transistor (OTFT) backplane for an electrophoretic display panel containing 192×150 pixels on a 6-in.-sized substrate. The average of mobilities of 36 OTFTs, which were taken from different locations of the backplane, was 0.44±0.08 cm^{2}·V^{-1}·s^{-1}, with a small deviation of 20%, over a 6-in.-size area comprising 28,800 OTFTs. This process providing high mobility and high uniformity can be achieved by simply maintaining the whole area of the substrate at a specific temperature (46 °C in this case) during drying of the droplets.

Hybrid Method for Analyzing the Torsional Vibration of One-Dimensional Phononic-Band-Gap Shafts

Lixia Li, Tianning Chen, Jiuhui Wu, Xiaopeng Wang, and Zhaofeng Wang — 2012-05-01T09:00:00+09:00

Authors: Lixia Li, Tianning Chen, Jiuhui Wu, Xiaopeng Wang, and Zhaofeng Wang
A hybrid method combining the transfer-matrix and lumped-mass methods is proposed to study the band gaps of torsional vibration in one-dimensional (1D) phononic band gap (PBG)-like shafts, which periodically arrange local resonant multilayer rings. The present method shows advantages over the transfer-matrix and lumped-mass methods for determining the inertia of rubber rings and fast convergence with less computational requirements. For light local resonators, the torsional band gaps, which were studied in three 1D PBG-like shafts by the hybrid method, agree well with those studied by the finite method. In addition, more precise evaluations of the starting frequency of the band gaps were carried out analytically. The methodology of the approach presented can also be employed to study the band gaps of bending and longitudinal waves.

Transparent Conductive Distributed Bragg Reflectors Composed of High and Low Refractive Index Transparent Conductive Films

Cheng-Chung Lee, Meng-Chi Li, Sheng-Hui Chen, and Chien-Cheng Kuo — 2012-05-01T09:00:00+09:00

Authors: Cheng-Chung Lee, Meng-Chi Li, Sheng-Hui Chen, and Chien-Cheng Kuo
This article has shown that the co-sputtering method and post-annealing treatment have successfully fabricated the transparent conductive distributed Bragg reflectors (TCDBR). The transparent conducting film, anatase Nb-doped TiO_{2} (TNO), which has a high refractive index can be combined with Al-doped ZnO (AZO) low refractive index transparent conducting films to make a TCDBR capable of transferring the current from electrode to semiconductor while still maintaining the advantage for the micro resonant cavity. The eight-period stack of AZO/TNO achieves a reflectivity of up to 90% centered at 550 nm and a resistivity of 1.88×10^{-3} Ω cm.

Buffer-Related Degradation Aspects of Single and Double-Heterostructure Quantum Well InAlN/GaN High-Electron-Mobility Transistors

2012-05-01T09:00:00+09:00

Authors: Jan Kuzmik, Stanislav Vitanov, Christian Dua, Jean-Francois Carlin, Clemens Ostermaier, Alexander Alexewicz, Gottfried Strasser, Dionyz Pogany, Erich Gornik, Nicolas Grandjean, Sylvain Delage, and Vassil Palankovski
We experimentally prove the viability of the concept of the double-heterostructure quantum well InAlN/GaN high-electron-mobility transistor (HEMT) for the device higher robustness and reliability. In the single quantum well InAlN/GaN HEMTs, the intrinsic channel resistance increases by 300% after 1 h off-state stress; much less degradation is observed in the double-heterostructure device with an AlGaN back barrier. Physics-based device simulation proves that the back barrier blocks the rate of carrier injection into the device buffer. However, whatever the quantum well design is, the energy of the injected electrons in the buffer of InAlN/GaN-based HEMTs is higher than that in the buffer of AlGaN/GaN HEMTs. This energy may be sufficient for releasing hydrogen from GaN point defects.

Simulation of Material Properties of Barium Titanate Single Crystal with Multidomain Structure Using Modified Time-Dependent Devonshire–Ginzburg–Landau Model

Syunji Imanaga and Kaoru Miura — 2012-04-27T09:00:00+09:00

Authors: Syunji Imanaga and Kaoru Miura
We simulated and compared the material properties of the tetragonal phase of barium titanate for two types of multidomain structures, namely, multidomain-1 including both 90 and 180° domains, and multidomain-2 including only the 180° domain, and a monodomain by using a modified time-dependent Devonshire–Ginzburg–Landau model of two dimensions. We found that the piezoelectric coefficient d_{12} and dielectric susceptibility η_{22} of muiltidomain-1 are about 6.5 times larger than those of the monodomain, and the large values of d_{12} and η_{22} of multidomain-1 are explained by considering its peculiar multidomain structure. Moreover, we found that the piezoelectric coefficient d_{22} of muiltidomain-2 before polling is about one-half that of the monodomain, and that of muiltidomain-2 after polling is about two times larger than that before polling, whereas the value of η_{22} before polling is three times larger than that after polling.

Thermo-Optical Tuning of Whispering Gallery Modes in Erbium:Ytterbium Doped Glass Microspheres to Arbitrary Probe Wavelengths

Amy Watkins, Jonathan Ward, and Síle Nic Chormaic — 2012-04-27T09:00:00+09:00

Authors: Amy Watkins, Jonathan Ward, and Síle Nic Chormaic
We present experimental results on an all-optical, thermally-assisted technique for broad range tuning of microsphere cavity resonance modes to arbitrary probe wavelengths. An erbium:ytterbium co-doped phosphate glass (Schott IOG-2) microsphere is pumped at 978 nm via the supporting stem and the heat generated by absorption of the pump light expands the cavity and changes the refractive index. This is a robust tuning method that decouples the pump from the probe and allows fine tuning of the microsphere's whispering gallery modes. Pump/probe experiments were performed to demonstrate thermo-optical tuning to specific probe wavelengths, including the ^{5}S_{1/2} F= 3 to ^{5}P_{3/2} F'= 4 laser cooling transition of rubidium-85. This is of particular interest for cavity quantum electrodynamics (QED)-type experiments, while the broad tuning range achievable is useful for integrated photonic devices, including sensors and modulators.

Ge Flat Layer Growth on Heavily Phosphorus-Doped Si(001) by Sputter Epitaxy

2012-04-27T09:00:00+09:00

Authors: Hiroaki Hanafusa, Nobumitsu Hirose, Akifumi Kasamatsu, Takashi Mimura, Toshiaki Matsui, and Yoshiyuki Suda
We have investigated layer-by-layer Ge growth methods on phosphorus (P)-doped Si(001) with our sputter epitaxy method at a growth temperature (T_{G}) of 350 °C. With the sputter epitaxy method, relaxed Ge islands are formed on P-doped 3.5 Ω cm Si with Ge–Si intermixing at the Ge/Si interface; however, a partially strained flat Ge layer is grown directly on P-doped 0.015 Ω cm Si. For comparison with a gas-source molecular beam epitaxy (GS-MBE) method using GeH_{4}, Ge islands are formed on 0.015 Ω cm Si at T_{G} = 350 °C. It has been suggested that the P dopants together with the sputter epitaxy method effectively suppress Ge islanding and induce Ge layer-by-layer growth.

Thresholds of Etchable Track Formation and Chemical Damage Parameters in Poly(ethylene terephthalate), Bisphenol A polycarbonate, and Poly(allyl diglycol carbonate) Films at the Stopping Powers Ranging from 10 to 12,000 keV/µm

2012-04-27T09:00:00+09:00

Authors: Tomoya Yamauchi, Yutaka Mori, Akira Morimoto, Masato Kanasaki, Keiji Oda, Satoshi Kodaira, Teruaki Konishi, Nakahiro Yasuda, Sachiko Tojo, Yoshihide Honda, and Rémi Barillon
The damage structure of latent tracks in poly(ethylene terephthalate) (PET) has been examined by Fourier transform infrared (FT-IR) measurements. Results are compared with those from previous studies on bisphenol A polycarbonate (PC) and poly(allyl diglycol carbonate) (PADC). These polymers are exposed to protons and heavy ions (He, C, Ne, Si, Ar, Fe, Kr, and Xe) in air with energies less than 6 MeV/n, as well as gamma rays from an intense Co-60 source. Chemical damage parameters, namely, damage density, which is the number of losses of considered functional groups per unit length of tracks, radial size of the track core, in which the considered chemical groups are lost, and radiation chemical yields (G values) for each group are evaluated as a function of the stopping power. It has been confirmed that latent tracks will be etchable when the radial track core size is larger than the distance between two adjacent breaking points of polymer chains. The predominant breaking points are the C–O bonds in ether, ester, and carbonate ester bonds.

Practical Guidance of Parameter Extraction for Device Simulation of Thin-Film Transistors

Mutsumi Kimura — 2012-04-25T09:00:00+09:00

Authors: Mutsumi Kimura
We introduce practical guidelines for parameter extraction in the device simulation of thin-film transistors. First, the deep trap density is extracted by fitting the subthreshold swing, the surface-fixed charge density by the turn-on voltage, and the tail trap density by the threshold current. Next, the carrier mobility is extracted by fitting the transconductance and the cross section of the trap states by the off current. This procedure is essential because the changes in the parameters extracted later do not affect the parameters extracted formerly and we do not have to iterate the fitting, which makes the parameter extraction speedy and robust against divergence. These practical guidelines are useful for device development, characteristic prospect, and process diagnosis.

Adsorption of Pyrazine on a Si(001) Surface Partially Covered with an Indium Dimer Structure

Masaru Shimomura and Chihiro Kunihara — 2012-04-25T09:00:00+09:00

Authors: Masaru Shimomura and Chihiro Kunihara
Pyrazine forms a molecular one-dimensional (1D) line on a bare Si(001)-2×1 surface across the Si dimer row. Indium also forms a 1D line across the Si dimer row. In this study, the adsorption of pyrazine on a Si(001)-2×1 surface on which the indium parallel dimer structure is formed was investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). It was found by STM that pyrazine adsorbates were predominantly located at the lateral neighboring sites of the indium line structure during the initial stage of adsorption. This preferential adsorption of pyrazine can enhance the formation of long linear chains of pyrazine along the indium lines.

Development of Low-Temperature Sintering Technique for Dye-Sensitized Solar Cells Combined with Dielectric Barrier Discharge Treatment

Shungo Zen, Yoshiyuki Teramoto, Ryo Ono, and Tetsuji Oda — 2012-04-25T09:00:00+09:00

Authors: Shungo Zen, Yoshiyuki Teramoto, Ryo Ono, and Tetsuji Oda
The manufacture of the dye-sensitized solar cell (DSSC) requires the sintering of TiO_{2} paste at 450–550 °C. High-temperature sintering is disadvantageous because it prevents the use of the materials with poor resistance to high sintering temperatures (e.g., substrate and transparent electrode). In this study, we develop a new technique of reducing the sintering temperature to 250–300 °C using dielectric barrier discharge (DBD) treatment. The DBD treatment of a 250–300 °C-sintered sample has the effects of removing the organic binder in the TiO_{2} paste, accelerating the necking of TiO_{2} nanoparticles, and chemically modifying the TiO_{2} surface. As a result, the energy conversion efficiency of low-temperature-sintered DSSC becomes approximately equivalent to 450–550 °C-sintered DSSCs. DBD treatment is also applied to a binder-free TiO_{2} paste that was developed for the low-temperature sintering of plastic substrate DSSCs. The energy conversion efficiency of the binder-free paste DSSC sintered at 150 °C is improved by a factor of 1.4 using DBD treatment.

Magnetic Alignment of Magnetically Biaxial Diamagnetic Rods under Rotating Magnetic Fields

Shu Tsukui and Tsunehisa Kimura — 2012-04-25T09:00:00+09:00

Authors: Shu Tsukui and Tsunehisa Kimura
The alignment behavior of magnetically biaxial diamagnetic rods under rotating magnetic fields is studied to elucidate the effects of particle shape and rotation speed on alignment manner. Three types of rod (ca. 1.1 mmφ × 3 mm) are prepared: (i) rod axes parallel to χ_{1}, (ii) parallel to χ_{2}, and (iii) parallel to χ_{3}, where χs are the principal axes of the diamagnetic susceptibility tensor and χ_{1} > χ_{2} > χ_{3}. The motion of the rod is recorded on video and the angles required for the comparison with simulation are measured. Simulation is performed by numerically solving a torque equation including magnetic and hydrodynamic torques. The experimental results show a good agreement with simulation results. It is shown that the χ_{3}-axis of rod sample (ii) does not align parallel to the axis of the rotating magnetic field under most experimental conditions; this is in marked contrast to the case with magnetically uniaxial particles (χ_{1} = χ_{2} > χ_{3}), for which the χ_{3}-axis aligns irrespective of particle shape and/or rotation speed. This observation is interpreted in terms of magnetic energy and orientation kinetics.

A Comparative Study on the Optical and Electrical Properties of Si-Doped Polar and Nonpolar GaN

Keun Man Song and Hogyoung Kim — 2012-04-24T09:00:00+09:00

Authors: Keun Man Song and Hogyoung Kim
Si-doped polar (c-plane) and nonpolar (a-plane) GaN layers grown by metal–organic vapor phase epitaxy (MOVPE) were comparatively investigated using photoluminescence (PL) and Hall-effect measurements. While c-plane GaN revealed both band-acceptor and donor–acceptor transitions, the PL spectra for a-plane GaN were related to extended defects such as basal stacking faults (BSFs) and prismatic stacking faults (PSFs). A new emission peak was observed at 3.361 eV in the Si-doped a-plane GaN, which was attributed to Si-doping-induced defects. The temperature-dependent Hall-effect measurements showed that for c-plane GaN, mobility was dominated by optical phonon and ionized impurity scattering at high and low temperature, respectively. Conversely, for a-plane GaN, the scattering mechanism due to dislocations was dominant at all temperatures.

Theoretical Evaluation of Ballistic Electron Transport in Field-Effect Transistors with Semiconducting Graphene Channels

2012-04-24T09:00:00+09:00

Authors: Hideaki Tsuchiya, Hiroshi Hosokawa, Ryūtaro Sako, Naomi Hasegawa, and Matsuto Ogawa
In this paper, we present a theoretical evaluation of ballistic electron transport in field-effect transistors (FETs) with semiconducting graphehe channels; bilayer graphenes (BLGs), monolayer graphene nanoribbons (MLGNRs), and bilayer graphene nanoribbons (BLGNRs). We found that the use of BLGNRs produces little advantage in either increasing the band gap energy or improving the device performance, as compared with a pristine BLG device. We also demonstrated that BLG-based FETs exhibit quite different behavior in the drain current versus gate voltage characteristics from that of MLGNR-FETs, since a distorted dispersion relation around the conduction band minima significantly affects the drain current property.

Translation from Schottky Barrier to Atomic Bridging-Type Surface Photovoltages in Cr-Aqueous-Solution-Rinsed Si(001) Wafers

Hirofumi Shimizu and Yuji Sanada — 2012-04-24T09:00:00+09:00

Authors: Hirofumi Shimizu and Yuji Sanada
The Cr(OH)_{3}/n-Si Schottky-barrier-type AC surface photovoltage (SPV) in n-type Si(001) wafers fades away during long air exposure at room temperature and/or thermal oxidation at 100 °C for a short time (10 min), indicating a collapse of the Schottky barrier. At 100 °C, the AC SPV reappears with a longer duration time in n-type Si wafers, explaining the occurrence and growth of a negative oxide charge because of the formation of an atomic bridging (CrOSi)^{-} or CrO^{2-} network reported previously. At 200 °C, the AC SPV approaches a strong inversion state in n-type Si. In contrast, in p-type Si(001) wafers, the AC SPV decreases with oxidation duration time at 100 °C. At 200 °C, the AC SPV completely disappears in p-type Si. This result explains why a positive fixed oxide charge in p-type Si was compensated for by the growth of a Cr-induced negative charge [(CrOSi)^{-} or CrO^{2-} network]. This reverse interrelation gives evidence that the translation occurs from the Schottky barrier to the atomic bridging AC SPV, and thus the Cr-induced negative charge can be proved to be described as (CrOSi)^{-} and/or CrO_{2}^{-} networks as well as (AlOSi)^{-} or (FeOSi)^{-} networks that were demonstrated previously.

Discriminated Detection of Nuclear Tracks Recorded on Multilayers of Photographic Emulsions with Different Sensitivities by Color-Development Method

Ken’ichi Kuge, Ryota Ito, Satoshi Kodaira, and Nakahiro Yasuda — 2012-04-24T09:00:00+09:00

Authors: Ken’ichi Kuge, Ryota Ito, Satoshi Kodaira, and Nakahiro Yasuda
We have developed a new method for the detection of nuclear tracks recorded on nuclear plates composed of multiple photographic emulsion layers. Each layer of these plates contained a photographic coupler revealing a different color after color development. The developed silver grains left behind in each layer were colored with differently colored dye clouds when the bleaching process was omitted in the color-development process. The three-dimensional structure of a track was obtained from the color change of the track. The track indicated a different grain density in each layer of different sensitivity, thus expanding the dynamic range of such nuclear plates. Accurate discrimination of particles with different deposit energies by using emulsions with different properties in each layer is also expected.

Synthesis and Magnetic Properties of NiSe, NiTe, CoSe, and CoTe

2012-04-23T09:00:00+09:00

Authors: Norio Umeyama, Madoka Tokumoto, Shota Yagi, Masatoshi Tomura, Kazuyasu Tokiwa, Takenori Fujii, Ryo Toda, Nobuaki Miyakawa, and Shin-Ichi Ikeda
Polycrystalline NiSe, NiTe, CoSe, and CoTe have been synthesized by two methods, i.e., (1) the solid-state reaction in an evacuated quartz ampoule (QA) and (2) the high-pressure (HP) technique (HP) in a Au capsule using a cubic anvil cell. All the obtained samples have the nickel arsenide-type hexagonal crystal structure, except CoTe (HP), and their estimated lattice parameters, a and c, show almost the same values within 0.8% in comparison between samples prepared by the QA method and those by the HP method. On the other hand, a distinct difference between samples prepared by QA and HP processes is found in the magnetization of NiSe and NiTe. In particular, for NiTe, the temperature dependence of magnetization indicates two transition temperatures at about 20 and 130 K in samples prepared by the HP process. However, samples of NiTe_{x} (x = 0.5, 0.66, 0.82, 1, 1.22, and 2) and NiTe containing Au prepared by QA process do not show similar magnetic orders in the temperature range between 2 and 300 K. Also, samples of NiSe (HP) show magnetic transition at ∼20 K, while those of NiSe (QA) show a magnetic inflection point at ∼10 K. To the best of our knowledge the remarkable difference in magnetic properties caused by the method of synthesis has not been reported. In this paper, we present comparative experimental results of magnetic, electric, and specific heat measurements of samples prepared by the two methods. A possible explanation for such a substantial difference in magnetic interaction will be discussed.

A New Two-Dimensional Analytical Threshold Voltage Model for Short-Channel Triple-Material Surrounding-Gate Metal–Oxide–Semiconductor Field-Effect Transistors

Hsin-Kai Wang, Sean Wu, Te-Kuang Chiang, and Maw-Shung Lee — 2012-04-23T09:00:00+09:00

Authors: Hsin-Kai Wang, Sean Wu, Te-Kuang Chiang, and Maw-Shung Lee
A new analytical model for the surface potential and threshold voltage of triple-material surrounding-gate (TM-SGT) metal–oxide–semiconductor field-effect transistors (MOSFETs) is proposed to investigate short-channel effects (SCEs). The TM-SGT MOSFET forms a two-step potential in the channel and effectively reduces the SCEs and the variation of threshold voltage compared with those of dual-material surrounding-gate (DM-SGT) and triple-material double-gate (TM-DG) MOSFETs. TM-SGT MOSFETs thus have better performance than DM-SGT and TM-DG MOSFETs.

Photocatalytic Activity of WO_{3} Films Crystallized by Postannealing in Air

Jyunya Takashima, Nobuto Oka, and Yuzo Shigesato — 2012-04-23T09:00:00+09:00

Authors: Jyunya Takashima, Nobuto Oka, and Yuzo Shigesato
We devised an effective method of deposition of photocatalytic WO_{3} films for the decomposition of volatile organic compounds. Amorphous WO_{3} films were deposited on unheated fused silica glass substrates by reactive DC magnetron sputtering with a W metal target, followed by crystallization through annealing at 300–800 °C in air. Under visible light irradiation, a film annealed at 400 °C proved significantly more effective than a WO_{3} film crystallized during deposition on a heated (800 °C) substrate for achieving photocatalytic decomposition of CH_{3}CHO. Even more remarkable photocatalytic results were obtained for a film that was loaded with Pt nanoparticles after postannealing.

Primary Factor Extracted for Anomalous Decline of Drain Current in Metal–Oxide–Semiconductor Field-Effect Transistors

Kazuhide Abe, Tadahiro Sasaki, and Kazuhiko Itaya — 2012-04-20T09:00:00+09:00

Authors: Kazuhide Abe, Tadahiro Sasaki, and Kazuhiko Itaya
A statistical approach has been exploratively applied to extract an influential factor of anomalous decreases in drain current observed in metal–oxide–semiconductor field-effect transistors with large channel widths. Since negative slopes were detected in drain current vs drain voltage (I_{d}–V_{ds}) curves even with negligible heat quantity or density, the self-heating effect was excluded as the primary factor. In contrast, the aspect ratio of the device areas showed a significant influence. These results support the validity of a hypothesis, namely, that acoustic standing waves are excited and thereby the probabilities of impact ionizations are synchronously magnified in the devices.

Uniform Dispersion of Liquid Crystal Droplets in the Polymer Matrix by Chemical Affinity Difference-Induced Phase Separation

Zheng-Guo Shen, Ji-Hoon Lee, and Tae-Hoon Yoon — 2012-04-20T09:00:00+09:00

Authors: Zheng-Guo Shen, Ji-Hoon Lee, and Tae-Hoon Yoon
We proposed a method to obtain uniformly dispersed liquid crystal (LC) droplets in the polymer matrix. Polymer spacers were formed on the bottom substrate and the LC–reactive monomer (RM) mixture was injected between the substrates in the isotropic phase. After cooling to the room temperature, the RM molecules which have higher chemical affinity to the polymer spacers were diffused to the polymer spacers. Simultaneously, the LC molecules were separated from the RM molecules and formed homogenously dispersed droplets with a uniform size. The phase retardation, mechanical tolerance, and response time of the cell suggested were examined.

Application of a Continued-Fraction-Based Theory to Line-Profile in Mn-Doped GaN Film

Jung-Il Park, Hyeong-Rag Lee, and Su-Ho Lee — 2012-04-20T09:00:00+09:00

Authors: Jung-Il Park, Hyeong-Rag Lee, and Su-Ho Lee
Starting with the Kubo formalism and using the projection operator technique (POT) introduced by Kawabata, the optical quantum transition line-profiles (QTLPs) formula for a Mn-doped wurtzite GaN film was derived as a function of temperature at a frequency of 9.49 GHz (X-band), on the basis of continued fraction representation (CFR) which is a counterpart of the conventional series expansion (CSE). Utilizing this formula we obtained the fine-structure parameter a - F = 9.4 ×10^{-4} cm^{-1} and fitting parameter ζ= 4.1. The optical quantum transition half-widths (QTHWs) obtained with the use of these parameters agrees quite well with the existing experimental result in the temperature region T > 20 K. The QTHWs increase with increasing temperature due to the interaction of electrons with optical phonons. Thus, the present technique is considered to be more convenient to explain the resonant system as in the case of other optical transition problems.

Near-Edge X-Ray Absorption Fine Structure Study of Vertically Aligned Carbon Nanotubes Grown by the Surface Decomposition of SiC

2012-04-20T09:00:00+09:00

Authors: Takahiro Maruyama, Yuki Ishiguro, Shigeya Nartitsuka, Wataru Norimatsu, Michiko Kusunoki, Kenta Amemiya, Hideshi Ishii, and Toshiaki Ohta
Vertically aligned carbon nanotubes (CNTs) grown by the surface decomposition of SiC were studied by angular-dependent C K-edge near-edge X-ray absorption fine structure spectroscopy (NEXAFS) with a linearly polarized X-ray beam. The NEXAFS spectra measured in total electron yield mode showed a distinct angular dependence on π^{*} and σ^{*} resonances and the orientation parameter was tentatively estimated to be 0.38, which is fairly larger than those reported for other vertically aligned CNTs grown by chemical vapor deposition. The high order of the vertical alignment of CNTs grown by the surface decomposition of SiC was demonstrated by NEXAFS measurements for the first time.

The Diagnosis Method for High-Energy Ion Beams Using Backscattered Particles for Laser-Driven Ion Acceleration Experiments

2012-04-20T09:00:00+09:00

Authors: Masato Kanasaki, Yuji Fukuda, Hironao Sakaki, Toshihiko Hori, Motonobu Tampo, Kiminori Kondo, Satoshi Kurashima, Tomihiro Kamiya, Keiji Oda, and Tomoya Yamauchi
A single CR-39 detector mounted on plastic plates is irradiated with a 100 MeV He ion beam. Although the beam energy is much greater than the detection threshold limit of the CR-39 detector, a large number of etch pits having elliptical openings are observed on the rear surface. Detailed investigations reveal that these etch pits are created by heavy ions inelastically backscattered from the plastic plates. This method allows a simple diagnosis of the ion beam profile and the presence of the high-energy component beyond the detection threshold limit of the CR-39 detector, especially in mixed-radiation fields such as laser-driven ion acceleration experiments.

Optical Characterization of Double Peak Behavior in 10-11 Semipolar Light-Emitting Diodes on Miscut m-Plane Sapphire Substrates

2012-04-19T09:00:00+09:00

Authors: Sang-Bae Choi, Si-Young Bae, Dong-Seon Lee, Bo Hyun Kong, Hyung Koun Cho, Jung-Hoon Song, Byung-Jun Ahn, John F. Keading, Shuji Nakamura, Steven P. DenBaars, and James S. Speck
{10-11} semipolar GaN-based light-emitting diodes (LEDs) grown on 1° miscut m-plane sapphires substrates via metal organic chemical vapor deposition showed undulated surface morphology with ridges and valleys. On the ridge regions, two dominant emission peaks, one at a shorter wavelength (∼438 nm) and one at a longer wavelength (∼490 nm), were observed using electroluminescence and micro-photoluminescence. In the valley regions, the longer peak was observed to be significantly quenched due to the grain boundary. The origin of the longer peak is believed to be not only inhomogeneous distribution of In composition in multiple quantum wells (MQWs) but also strong localization around the ridge region. Moreover, thickness variation of faceted MQWs could be associated with the peak broadening in 10-11 semipolar LEDs. The results were also confirmed by cathodoluminescence and cross-sectional transmission electron microscopy.

Monomode Optical Waveguides in Yb^{3+}-Doped Silicate Glasses Produced by Low-Dose Carbon Ion Implantation

Chun-Xiao Liu, Shu Cheng, Wei-Nan Li, Wei Wei, and Bo Peng — 2012-04-19T09:00:00+09:00

Authors: Chun-Xiao Liu, Shu Cheng, Wei-Nan Li, Wei Wei, and Bo Peng
The planar waveguide has been fabricated in the Yb^{3+}-doped silicate glass by 4.0 MeV C^{2+} ion implantation at a dose of 2×10^{14} ions/cm^{2}. The guided modes are measured using a model 2010 prism coupler at 633 nm. The near-field profiles of the planar waveguide are obtained with an end-face coupling system. The refractive index profile of the waveguide is reconstructed by the intensity calculation method, which shows a typical “enhanced well + barrier” distribution. The SRIM'2006 code is carried out to simulate the energy loss during the implantation in order to obtain a better understanding of the waveguide formation. After post-implantation treatment at 260 °C for 1 h, the waveguide possesses a propagation loss of ∼1.42 dB/cm. The acceptable guiding properties suggest that further waveguide lasers may be realized on the C-implanted Yb^{3+}-doped silicate glass waveguides.

Optical and Transport Anisotropy in Poly(9,9'-dioctyl-fluorene-alt-bithiophene) Films Prepared by Floating Film Transfer Method

Arnaud Dauendorffer, Shuichi Nagamatsu, Wataru Takashima, and Keiichi Kaneto — 2012-04-19T09:00:00+09:00

Authors: Arnaud Dauendorffer, Shuichi Nagamatsu, Wataru Takashima, and Keiichi Kaneto
We demonstrated the fabrication of self-aligned poly(9,9'-dioctyl-fluorene-alt-bithiophene) copolymer (F8T2) thin films at ambient temperature with a new solution-process technique named floating film transfer method (FTM). Atomic force microscope topography and polarized absorption spectroscopy showed that the polymer main chains aligned perpendicularly to the film propagation direction during the fabrication process. FTM films presented absorption dichroic ratios slightly below 3. Top-contact/bottom-gate field effect transistors made with FTM films exhibited anisotropic transport properties with a hole mobility along the aligned direction of F8T2 main chains of 2.2×10^{-3} cm^{2}/(V·s), which was around 2.5 times greater than that along the perpendicular direction. Dichroic and transport anisotropy ratios were further enhanced up to 7–8 by thermal annealing, although the mobility improvement remained limited due to possible trapping effect at domain boundaries.

Ultra-Conformal Metal Coating on High-Aspect-Ratio Three-Dimensional Structures Using Supercritical Fluid: Controlled Selectivity/Non-Selectivity

2012-04-19T09:00:00+09:00

Authors: Takeshi Momose, Takeshi Uejima, Hideo Yamada, Yukihiro Shimogaki, and Masakazu Sugiyama
Underlayer dependence can be controlled for supercritical fluid deposition (SCFD) of Cu. SCFD, which has a remarkable potential for ultra-conformal deposition and gap-filling, has previously required a metallic underlayer to initiate deposition. Here, this constraint has been overcome by depositing a novel catalytic layer, CuMn_{x}O_{y}, onto a semiconducting and insulating substrate. The stoichiometry of CuMn_{x}O_{y} affected both the morphology of CuMn_{x}O_{y} film and the catalytic effect on succeeding SCFD of Cu. By using this technique of depositing CuMn_{x}O_{y} as a catalytic layer, conformal SCFD of Cu was achieved on high-aspect-ratio trenches (aspect ratio 50) whose surfaces were SiO_{2}. In conclusion, a CuMn_{x}O_{y} film with graded stoichiometry in the depth direction might improve the adhesion between Cu and an insulative underlayer.

10 Gbps Colorless Optical Source in Wavelength-Division Multiplexed Passive Optical Networks for Monolithic Integration of Deep-Ridge Waveguide Electroabsorption Modulator with Planar Buried-Heterostructure Semiconductor Optical Amplifier

Dong Churl Kim, Ki Soo Kim, Hyun-Soo Kim, Byung-Seok Choi, and O-Kyun Kwon — 2012-04-18T09:00:00+09:00

Authors: Dong Churl Kim, Ki Soo Kim, Hyun-Soo Kim, Byung-Seok Choi, and O-Kyun Kwon
For the 10 Gbps colorless optical source in wavelength-division multiplexed passive optical networks (WDM-PONs), we have fabricated a semiconductor optical amplifier-reflective electorabsorption modulator (SOA-REAM) by monolithic integration of deep-ridge waveguide REAM (DRW-REAM) with planar buried-heterostructure (PBH) SOA using a PNP-current blocking layer. The SOA-REAM has a spot-size convertor for easy fiber coupling. Using a butterfly module with an SMA connector, we have packaged the SOA-REAM. At a -10 dBm input power of 1550 nm, the saturation output power is about 6 dBm. At 10.7 Gbps, we can obtain clear eye diagrams, and the power penalty at 10^{-9} bit-error rate (BER) after 20 km transmission is less than 1 dB over 35 nm.

Crack-Free AlN/GaN Distributed Bragg Reflectors on AlN Templates

2012-04-18T09:00:00+09:00

Authors: Kouta Yagi, Mitsuru Kaga, Kouji Yamashita, Kenichirou Takeda, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Hiroshi Amano, and Isamu Akasaki
We have demonstrated crack-free 30-pair-AlN/GaN distributed Bragg reflectors (DBRs) grown on AlN templates for the first time. A reasonably high reflectivity of 97.5% was obtained. X-ray diffraction measurements revealed that the AlN templates cause compressive stress in DBRs. At the same time, the AlN/GaN DBRs were found to relax to average AlGaN alloys with AlN mole fractions determined by the thickness ratio of the AlN layer to one pair of AlN and GaN in DBRs regardless of the underlying template, AlN or GaN.

Efficient Ultraviolet Rotational Raman Lidar for Temperature Profiling of the Planetary Boundary Layer

2012-04-18T09:00:00+09:00

Authors: Masaharu Imaki, Hisaji Kawai, Tadashi Kato, Toshikazu Hasegawa, and Takao Kobayashi
An efficient rotational Raman scattering lidar using an ultraviolet-wavelength laser has been developed for temperature profile measurement of the planetary boundary layer in the lower troposphere. In this system, the high rejection of intense elastic Rayleigh and Mie backscattering was realized by a rotational Raman spectrometer using a diffraction grating and dual interference filters. Temperature measurement in thin cloud was demonstrated, and it was shown that the temperature profile obtained by lidar measurement is in good agreement with that obtained by radiosonde measurement. A statistical error of less than 1 K was obtained up to 2.5 km height in daytime measurement and up to 4.6 km height in nighttime measurement in clear air with an observation time of 16 min.

Simulation Study on Insulated Gate Bipolar Transistor Turn-Off Oscillations

Shigeto Fujita — 2012-04-18T09:00:00+09:00

Authors: Shigeto Fujita
High-frequency voltage oscillation is occasionally observed in insulated gate bipolar transistors during a turn-off operation. The turn-off oscillation generation was explained by the plasma extraction transit time oscillation theory. Its basic mechanism was the negative resistance creation. A negative RF power, which meant that the insulated gate bipolar transistor showed a “negative resistance”, was generated by the trapezoidal current density induced by holes and the RF voltage applied to the insulated gate bipolar transistor. However, the author showed that the induced current density oscillates with an almost negative phase compared with the RF voltage oscillation. He carried out an insulated gate bipolar transistor turn-off oscillation simulation using simplified simulation models. In this work, he showed the generation of the negative resistance and the turn-off oscillation in detail. He also showed the common and different points between his results and the plasma extraction transit time oscillation theory.

Influence of Interfacial Tantalum Oxynitride on Resistive Switching of Cu/Cu–SiO_{2}/TaN

Shyankay Jou and Ming-En Han — 2012-04-18T09:00:00+09:00

Authors: Shyankay Jou and Ming-En Han
We demonstrate reversible switching of the resistance of Cu/Cu–SiO_{2}/TaN cells with and without an interfacial tantalum oxynitride (TaON) layer. The TaN, Cu–SiO_{2}, and Cu layers were prepared by sputter deposition, and the TaON layer was produced by plasma oxidation of the TaN surface. Both cells demonstrated bipolar switching between the high resistance state (HRS) and the low resistance state (LRS). The Cu/Cu–SiO_{2}/TaN cell had set voltages of approximately around +1.0 V, reset voltages of approximately around -0.6 V, and resistance ratios (R_{HRS}/R_{LRS}) of about 6 to 8. By inserting a thin TaON layer between the Cu–SiO_{2} and TaN in the cell, R_{HRS}/R_{LRS} of the Cu/Cu–SiO_{2}/TaON/TaN cell was increased to above 400, and the set and reset voltages were decreased to about +0.3 and -0.2 V, respectively. Adding the interfacial TaON layer also improved the endurance of the cell. Furthermore, the conduction mechanisms for the Cu/Cu–SiO_{2}/TaN cells with and without an interfacial TaON layer were discussed.

Computational Nano-Materials Design of Low Cost and High Efficiency Cu_{2}ZnSn[Se_{1-x}S_{x}]_{4} Photovoltaic Solar Cells by Self-Organized Two-Dimensional Spinodal Nanodecomposition

Yoshimasa Tani, Kazunori Sato, and Hiroshi Katayama-Yoshida — 2012-04-17T09:00:00+09:00

Authors: Yoshimasa Tani, Kazunori Sato, and Hiroshi Katayama-Yoshida
We propose the possibility of spinodal nanodecomposition in Cu_{2}ZnSn[Se_{1-x}S_{x}]_{4} (CZTSeS) for high efficiency photovoltaic solar cells, based on the first-principles calculations within the self-interaction-corrected local density approximation. By using the Korringa–Kohn–Rostoker coherent potential approximation method, electronic structures of CZTSeS are calculated. Due to the calculated positive mixing energy and type II band alignment between Cu_{2}ZnSnSe_{4} and Cu_{2}ZnSnS_{4}, we can expect that the efficiency of CZTSeS becomes higher by spinodal nano-decomposition. Then we simulate the self-organized two-dimensional spinodal nanodecomposition by Monte Carlo method using the Ising model with chemical pair interactions calculated from the first principles.

Fabrication and Characterization of Bragg Reflector Slow-Light Waveguide with Oxide Lateral Confinement

Ayumi Fuchida, Akihiro Matsutani, and Fumio Koyama — 2012-04-17T09:00:00+09:00

Authors: Ayumi Fuchida, Akihiro Matsutani, and Fumio Koyama
Slowing light in Bragg reflector waveguides enables us to miniaturize optical devices. A platform of low-loss slow-light waveguides with lateral optical confinement is required. We propose and fabricate a slow-light waveguide with lateral oxide confinement using an equivalent index difference in a lateral direction. The coupling and propagation losses are evaluated from the waveguide length dependence of insertion losses. The propagation loss is in the range of 0.1 dB/µm for transverse magnetic (TM) modes. Also, it is predicted that the propagation loss can be reduced if we replace a top Au/distributed Bragg reflector (DBR) hybrid mirror with a Si/SiO_{2} DBR.

Shape Control of Trenched 4H-SiC C-Face by Thermal Chlorine Etching

Hidenori Koketsu, Tomoaki Hatayama, Hiroshi Yano, and Takashi Fuyuki — 2012-04-17T09:00:00+09:00

Authors: Hidenori Koketsu, Tomoaki Hatayama, Hiroshi Yano, and Takashi Fuyuki
The shape control inside a trenched 4H-SiC by atmospheric-pressure chlorine (Cl_{2}) etching has been investigated. The trench fabricated by a plasma process on the 4H-SiC(000-1) C-face with 4°-off toward [11-20] was used. The inside of the 4H-SiC trench was thermally etched in Cl_{2} ambience at 900 °C. The subtrenches intentionally formed by the plasma process were successfully eliminated along with thermal Cl_{2} etching. With further Cl_{2} etching, the 4°-off (000-1) C-face at the trench bottom disappeared and the V-shaped bottom with a specific angle for the (000-1) basal plane was formed. The mechanism underlying the change inside the trench shape is discussed in comparison with the off-angle dependence of Cl_{2} etching rate.

Topographic Contrast in Force Modulation Atomic Force Microscopy Images

Chunlai Yang, Cheng Zheng, Yuhang Chen, and Wenhao Huang — 2012-04-17T09:00:00+09:00

Authors: Chunlai Yang, Cheng Zheng, Yuhang Chen, and Wenhao Huang
Topographic influences on force modulation microscopy (FMM) amplitude image contrasts have been investigated. Experimental results and a simple model analysis demonstrate that the amplitude has a close relevance to the x-derivative of sample topography. When the tip sample is in a single-point contact and the mechanical properties of the sample are homogeneous, the contrasts of the amplitude and x-derivative topography are almost the same. In addition, the amplitude contrast is reversed when the scan direction is opposite. When the tip sample is in a multipoint contact, the amplitude at the multipoint contact region increases markedly and the scan-direction relevant contrast reversion is still distinguishable. These results can help in the interpretation of FMM data accurately.

Effect of Frequency on the Change in Backscattered Ultrasound Energy as a Function of Temperature

Po-Hsiang Tsui and Yu-Ting Chien — 2012-04-17T09:00:00+09:00

Authors: Po-Hsiang Tsui and Yu-Ting Chien
Clinical trials have demonstrated that hyperthermia improves cancer treatments. Previous studies have developed temperature imaging methods based on the change in the backscattered energy (CBE) of ultrasound in order to monitor temperature variations during hyperthermia. The CBE with temperature is primarily due to the temperature dependency of the backscattering coefficient, which largely depends on the ultrasound frequency. This study explored the effect of frequency on the CBE as a function of temperature. Phantom experiments involving uniform heating from 37 to 45 °C were carried out in a temperature-regulated water tank, and the raw backscattered signals were acquired using ultrasound transducers with center frequencies of 5, 10, and 15 MHz for CBE imaging. The compensation of echo shift due to temperature increase was not made for simplifying the algorithm. In the condition without motion compensation, the results showed that the absolute value of the CBE (ACBE) increases with increasing temperature. The dynamic range of the ACBE at the focus of the transducer between 37 and 45 °C increased from 5.6 to 10 dB when the ultrasound frequency increased from 5 to 15 MHz, demonstrating that the sensitivity of the CBE image in indicating the temperature variation may increase with the ultrasound frequency. However, the dynamic range of the ACBE over the same temperature range increased from only 5.5 to 6.2 dB when the CBE data were acquired from the far field of the transducer. This indicates that the beam diffraction of the transducer may reduce the dependence of the CBE on frequency, suggesting that the beam diffraction effect should be taken into account when CBE imaging employs a high-frequency transducer for sensitive temperature detection.

Rotation-Symmetric Multispot Focusing Phase-Shifted Grating Coupler for Integrated Semiconductor Laser

Kengo Uenishi, Masahiro Uemukai, and Toshiaki Suhara — 2012-04-17T09:00:00+09:00

Authors: Kengo Uenishi, Masahiro Uemukai, and Toshiaki Suhara
Rotation-symmetric multispot focusing grating couplers with periodic binary phase modulation are designed and fabricated. The functions of 60 and 45° rotation-symmetric multispot focusing with the same spot intensities were demonstrated.

Quantitative Analysis of Surface Morphology of Boron-Doped Zinc Oxide for Microcrystalline Silicon Solar Cells

2012-04-13T09:00:00+09:00

Authors: Taweewat Krajangsang, Shuichi Hiza, Teruaki Hayashi, Ihsanul Afdi Yunaz, Aswin Hongsingthong, Shinsuke Miyajima, and Makoto Konagai
The optimization of textured boron-doped conductive zinc oxide (ZnO:B) films deposited by metal organic chemical vapor deposition (MOCVD) for hydrogenated microcrystalline silicon (µc-Si:H) solar cells was performed. We found that the argon (Ar) plasma treatment of a textured ZnO:B substrate is effective in improving the open-circuit voltage and fill factor of µc-Si:H solar cells. We proposed (tanθ)/λ^{2} as an evaluation factor and found that there is a clear correlation between the (tanθ)/λ^{2} of textured ZnO:B films and the open-circuit voltage of µc-Si:H solar cells. Moreover, the effect of the surface morphology of a textured ZnO:B substrate on the growth of intrinsic hydrogenated amorphous silicon (i-a-Si:H) top layers was examined to obtain the optimum conditions for preparing a-Si:H/µc-Si:H tandem solar cells. We confirmed that our proposed evaluation factor (tanθ)/λ^{2} could be used to obtain the surface morphology of i-a-Si:H top layers that are appropriate for µc-Si:H bottom-cell deposition.

Three-Dimensional Reciprocal-Lattice Analysis Using Azimuth-Scan Reflection High-Energy Electron Diffraction: Determination of Complex Crystal Orientations of Al Grains on Si(111) Surface

Ken Hattori, Hideo Oi, Kota Tanaka, Tomohiro Kumagai, and Hiroshi Daimon — 2012-04-13T09:00:00+09:00

Authors: Ken Hattori, Hideo Oi, Kota Tanaka, Tomohiro Kumagai, and Hiroshi Daimon
We have applied a three-dimensional (3D) reciprocal-lattice analysis method using a typical reflection high-energy electron diffraction (RHEED) system – all RHEED patterns in scanning sample-surface azimuth are converted into 3D reciprocal-lattice space. This analysis method can determine complex crystal orientations of nanoclusters, islands, and grains with multiple domains, which are difficult to obtain from a small number of non-converted two-dimensional RHEED patterns. For an Al-deposited Si(111) surface followed by annealing, we successfully determined new crystal orientations of Al grains: Al(001), Al(012) and Al(011) ∥ Si(111) with Al[100] ∥ Si<0-11>. The typical acquisition time of 3D RHEED patterns is 10–20 min, which is shorter than that by a standard X-ray diffraction system with φ and ω scans for 3D reciprocal-lattice mapping. This is one of the advantages of this analysis method, in addition to the convenient observation of in situ vacuum-fabricated nanocrystals on substrate surfaces with high sensitivity.

Self-Organized Nanostructures and High Blocking Temperatures in MgO-Based d^{0} Ferromagnets

2012-04-12T09:00:00+09:00

Authors: Masayoshi Seike, Van An Dinh, Tetsuya Fukushima, Kazunori Sato, and Hiroshi Katayama-Yoshida
We propose a new mechanism explaining the magnetic properties of MgO-based d^{0} ferromagnets determined from multi-scale simulations. Chemical pair interactions between N atoms in Mg(O,N) and Mg vacancies (V_{Mg}) in (Mg,V_{Mg})O were calculated using a generalized gradient approximation and the VASP code. Monte Carlo simulations of the crystal growth were performed, using the Ising model, to predict the favored configurations of dopant distribution. It was found that self-organized nanowires can be formed both in Mg(O,N) and (Mg,V_{Mg})O under layer-by-layer crystal growth, which suggests high blocking temperatures can be obtained in these d^{0} ferromagnets by spinodal nanodecomposition.

Synthesis of Nitrogen-Doped Graphene by Plasma-Enhanced Chemical Vapor Deposition

Tomo-o Terasawa and Koichiro Saiki — 2012-04-12T09:00:00+09:00

Authors: Tomo-o Terasawa and Koichiro Saiki
Synthesis of nitrogen-doped graphene on Cu foils by plasma-enhanced chemical vapor deposition (PE-CVD) and the growth mechanism of doped graphene were investigated. Nitrogen atoms are incorporated into the graphene lattice and most of them exist at a graphitic (quaternary) site. Plasma reaction facilitates the doping of nitrogen atoms even at a substrate temperature as high as 950 °C. Doped nitrogen atoms seem to distort the graphene lattice, which causes island-like growth rather than a layer-by-layer growth.

Effects of Plasma Processes on the Characteristics of Optical Device Structures Based on GaAs

Akio Watanabe, Fumitaro Ishikawa, and Masahiko Kondow — 2012-04-12T09:00:00+09:00

Authors: Akio Watanabe, Fumitaro Ishikawa, and Masahiko Kondow
We investigate the effects of inductively coupled O_{2} plasma ashing, capacitively coupled C_{3}F_{8} plasma etching, and capacitively coupled C_{3}F_{8}/O_{2} plasma etching on the optical and electrical characteristics of GaAs-related optical device structures. The O_{2} plasma ashing produces non radiative recombination centers close to the sample surface. The sample with a cap AlGaAs layer prevents the degradation of photoluminescence (PL) intensity, probably inhibiting the penetration of damaging ions into the buried quantum well. The C_{3}F_{8} plasma etching also degrades the PL intensity; however, under moderate conditions, the effect of non radiative surface recombination can be suppressed by the formation of a surface oxide layer. On the other hand, the formation of oxide increases the specific contact resistance (ρ_{c}) of the electrode. The etching with C_{3}F_{8}/O_{2} mixed plasma also deteriorates the optical characteristics presumably owing to the synthesized impact of the constituent gases, while it has limited effect on ρ_{c}.

Carbon Nanotube Research: Past and Future

Morinobu Endo — 2012-04-06T09:00:00+09:00

Authors: Morinobu Endo
In this paper, my experience of over 30 years in carbon materials and carbon nanotube (CNT) researches is reported. Moreover, an overview of the background of the development of CNT synthesis, the present status of CNT science and technology, and the future prospect of CNTs are described.

Study of Active Micromixer Driven by Electrothermal Force

2012-04-06T09:00:00+09:00

Authors: Kuan-Rong Huang, Jeng-Shian Chang, Sheng D. Chao, Tzong-Shyan Wung, and Kuang-Chong Wu
Biochemical applications of microchips often require a rapid mixing of different fluid samples. At the microscale level, fluid flow is usually a highly ordered laminar flow and diffusion is the primary mechanism for mixing owing to the lack of disturbances, yielding inefficiency for practical biochemical analysis. In this work, we design a prototype active micromixer by employing the electrothermal effect. We apply to the flow microchannel a non-uniform AC electric field, which can generate an electrothermal force on the fluid flow and induce vortex pairs for enhancing mixing efficiency. The performance of this active micromixer is studied and compared, under the same mixing quality, with that of a conventional passive micromixer of the same size with obstacles in the flow channel by three-dimensional finite element simulations. The numerical results show that the pressure drop between the inlet and the outlet for the active micromixer is much less than (only 3000th) that for the passive micro-mixer with the same mixing quality. To obtain an optimal mixing quality, we have systematically studied the mixing quality by varying the geometrical arrangements of the electrodes. An almost complete mixing can be obtained using a specific design. Moreover, the temperature increases around the electrodes are lower than 3 K, which does not adversely affect the biochemical analysis. It is suggested that the prototype active micromixer designed is promising and effective and useful for biochemical analysis.

Characterization of Photoexcited Carriers and Thermal Properties of Nanoparticulate TiO_{2} Film Using Heterodyne Transient Grating Method

Hiroaki Hata, Kenji Katayama, Qing Shen, and Taro Toyoda — 2012-04-05T09:00:00+09:00

Authors: Hiroaki Hata, Kenji Katayama, Qing Shen, and Taro Toyoda
Diffusion of photoexcited carriers and the subsequent thermal diffusion by photoexcitation of a nanoparticulate TiO_{2} thin film were observed by the heterodyne transient grating (HD-TG) method. The observed HD-TG signal showed that the photoexcited carriers were generated inhomogeneously in the depth direction and they diffused both in the depth and parallel directions of the film. The diffusion processes were analyzed using a two-dimensional diffusion model. The thermal profile generated by the relaxation of the photoexcited carriers was treated by the same model. It was found that the effective diffusivities of the photoexcited carriers and heat decreased as the size of the nanoparticles in the film increased. It is suggested that the transport properties of the photoexcited carriers and heat are dominated by the inter-particulate resistance.

Effect of Nucleation Layer of Photocatalytic TiO_{2} Thin Film Prepared by Two-Step Deposition Using Radical-Assisted Sputtering

2012-04-05T09:00:00+09:00

Authors: Daisuke Noguchi, Yukie Higashimaru, Tomohiro Eto, Kazuya Kodama, Shoji Fukudome, Yoshihiko Kawano, Fumihiro Sei, and Ichiro Siono
A nucleation layer forms in the nucleation step (the first step) of a two-step deposition method that we have developed for forming TiO_{2} thin films. We found that the nucleation layer affects the crystallinity of TiO_{2} thin films during the growth step (the second step). The crystallinity of the growth layer can be controlled by varying the kinetic energy of the sputter particles when they arrive at the substrate in the nucleation step. Since the nucleation density varies with the kinetic energy, the crystallinity is thought to improve, owing to the improvement in the nucleation density.

Properties of Inductively Coupled Radio Frequency CH_{4}/H_{2} Plasmas: Experiments and Global Model

Takashi Kimura and Hiroki Kasugai — 2012-04-05T09:00:00+09:00

Authors: Takashi Kimura and Hiroki Kasugai
Experiments with a Langmuir probe and optical emission spectroscopy combined with actinometry are carried out in inductively coupled rf (13.56 MHz) CH_{4}/H_{2} plasmas at three total pressures of 25, 50, and 100 mTorr for hydrogen fractions ranging from 0 to 80%. The measured electron density gradually decreases with increasing hydrogen fraction, whereas the measured effective electron temperature slightly increases with hydrogen fraction. The density of hydrogen atoms estimated by actinometry does not strongly depend on hydrogen fraction. The high density of hydrogen molecules can be expected even in CH_{4} plasmas from the optical intensity emitted from the excited hydrogen molecules. A global model is analyzed in order to understand the plasma chemistry in CH_{4}/H_{2} plasmas. In the model, the dominant neutral species are always hydrogen and CH_{4} molecules, followed by hydrogen atoms and hydrocarbons, such as C_{2}H_{n} (n=1, 2, and 4). On the other hand, the dominant ions are CH_{5}^{+}, C_{2}H^{+}, C_{2}H_{3}^{+}, C_{2}H_{5}^{+}, and C_{3}H_{5}^{+} at low hydrogen fraction, whereas H_{3}^{+} ions become dominant ion species as hydrogen fraction increases.

Ultrathin Reflective Flexible Liquid Crystal Display Film

Kang-Hung Liu and Han-Ping D. Shieh — 2012-04-04T09:00:00+09:00

Authors: Kang-Hung Liu and Han-Ping D. Shieh
In this investigation, we present a thin reflective liquid crystal film with a mixed-mode twisted nematic mode. A low-temperature alignment process is used to obtain good orientation of the liquid crystal molecules. A microcell process is utilized to maintain a uniform cell gap of the flexible display under various bending conditions. To simplify the structure of a flexible mixed-mode twisted nematic liquid crystal display film, a layer of Zeonor optical plastic material is used in place of conventional plastic substrates; this material exhibits quarter wave retardation. The ultrathin device exhibits good cell gap uniformity, a high reflectivity of 35%, and a short response time of 6.67 ms.

Relationship between Concentration of Initiator and Image-Sticking Phenomenon of Polymer-Sustained-Alignment Liquid Crystal Displays

Yohei Nakanishi and Kenji Okamoto — 2012-04-04T09:00:00+09:00

Authors: Yohei Nakanishi and Kenji Okamoto
We investigated the image-sticking phenomenon of polymer-sustained-alignment liquid crystal displays (PSA-LCDs). According to our experimental results, the image-sticking level of PSA-LCDs depends on the concentration of the photoinitiator in the liquid crystal of PSA-LCDs and the best concentration of the photoinitiator was zero. We found that polymerization of the monomer occurs without the photoinitiator, and clarified the mechanism of polymerization.

Effects of Electrospun TiO_{2} Nanowires Mixed in Nanoparticle-Based Electrode for Dye-Sensitized Solar Cells

Chieko Shimada, Koji Kitamura, and Seimei Shiratori — 2012-04-04T09:00:00+09:00

Authors: Chieko Shimada, Koji Kitamura, and Seimei Shiratori
In this article, we report the improvement of energy conversion efficiency by a simple process for dye-sensitized solar cells (DSSCs). Some previous studies were reported in which TiO_{2} nanowires were used in the place of TiO_{2} nanoparticles as a TiO_{2} electrode because nanowires possess a good electron transport property. However, if larger sizes of nanowires are used for the TiO_{2} electrode, a large void between nanowires and a decrease in surface area are observed. To solve this problem, we report a TiO_{2} nanoparticle/nanowire hybrid electrode for DSSCs, which showed both a good electron transport property and dye adsorption. TiO_{2} nanofibers were fabricated by an electrospinning method and sol–gel techniques. TiO_{2} nanowires, whose diameters were controlled by varying the polymer concentration in the electrospinning solution, were successfully applied to DSSCs. We examine how TiO_{2} nanowires can work in the TiO_{2} electrode. In this study, we demonstrated that this hybrid electrode has an advantage in the efficiency of DSSCs.

A New Collinear-Type Energy-Filtered X-ray Photoemission Electron Microscope Equipped with a Multi-Pole Aberration-Corrected Air-Core Coil Wien Filter

2012-04-04T09:00:00+09:00

Authors: Takeshi Miyamoto, Takahiro Wada, Hironobu Niimi, Shushi Suzuki, Makoto Kato, Masato Kudo, and Kiyotaka Asakura
We present the prototype of a new, collinear-type energy-filtered X-ray photoemission electron microscope (EXPEEM) using a multi-pole, aberration-corrected air-core coil Wien filter (WF) analyzer. We have designed the new WF with 12-pole electrodes and magnetic poles to reduce spherical aberrations and fringe effects. We assess the performance of the WF using an electron energy analyzer for PEEM. The sensitivity is enhanced 10–100 fold compared with a simple, two electrodes plus two magnetic poles type WF. Cu 2p_{3/2} and Au 4f_{7/2} photoelectron energy selected images are obtained in a laboratory-scale source within several minutes. The energy and spatial resolutions of our prototype EXPEEM are estimated to be 3 eV and 7 µm, respectively.

Low-Voltage Mach–Zehnder Modulator with InGaAs/InAlAs Five-Layer Asymmetric Coupled Quantum Well

2012-04-03T09:00:00+09:00

Authors: Taro Arakawa, Takehiro Hariki, Yoshimichi Amma, Masayasu Fukuoka, Motoki Ushigome, and Kunio Tada
We have demonstrated a low-voltage Mach–Zehnder (MZ) modulator with a multiple InGaAs/InAlAs five-layer asymmetric coupled quantum well (FACQW) for 1.55 µm wavelength. The FACQW is expected to exhibit a large electrorefractive index change owing to its unique behavior of the quantum-confined Stark effect. The MZ modulator with ridge waveguides was fabricated by molecular beam epitaxy and wet etching. The product of a half-wave voltage and a phase shifter length (V_{π}L) was as low as 1.2 V·mm in DC modulation. In addition, we discussed the degradation of the electrorefractive index change due to the nonuniformity of an electric field in the core layer and proposed a novel combined multiple FACQW structure to prevent the degradation.

Theoretical Analysis on Mechanical Deformation of Membrane-Based Photomask Blanks

Kenji Marumoto, Sunao Aya, Hedeki Yabe, Tatsunori Okada, and Hiroaki Sumitani — 2012-04-03T09:00:00+09:00

Authors: Kenji Marumoto, Sunao Aya, Hedeki Yabe, Tatsunori Okada, and Hiroaki Sumitani
Membrane-based photomask is used in proximity X-ray lithography including that in LIGA (Lithographie, Galvanoformung und Abformung) process, and near-field photolithography. In this article, out-of-plane deformation (OPD) and in-plane displacement (IPD) of membrane-based photomask blanks are theoretically analyzed to obtain the mask blanks with flat front surface and low stress absorber film. First, we derived the equations of OPD and IPD for the processing steps of membrane-based photomask such as film deposition, back-etching and bonding, using a theory of symmetrical bending of circular plates with a coaxial circular hole and that of deformation of cylinder under hydrostatic pressure. The validity of the equations was proved by comparing the calculation results with experimental ones. Using these equations, we investigated the relation between the geometry of the mask blanks and the distortions generally, and gave the criterion to attain the flat front surface. Moreover, the absorber stress-bias required to obtain zero-stress on finished mask blanks was also calculated and it has been found that only little stress-bias was required for adequate hole size of support plate.

Mn_{2}O_{3} Slurry Achieving Reduction of Slurry Waste

2012-04-03T09:00:00+09:00

Authors: Sadahiro Kishii, Ko Nakamura, Kenzo Hanawa, Satoru Watanabe, Yoshihiro Arimoto, Syuhei Kurokawa, and Toshiro K. Doi
Fumed silica is widely used for SiO_{2} chemical mechanical polishing (CMP). In semiconductor processes, only fresh slurry is used, the used slurry being disposed of. We have demonstrated that Mn_{2}O_{3} abrasive slurry polishes dielectric SiO_{2} film, giving 4 times the removal rate of conventional fumed silica slurry. The higher removal rate reduces the total amount of slurry used, consequently reducing the amount of used slurry waste. The removal rate of Mn_{2}O_{3} slurry remains constant for solid concentrations between l and 10 wt %, and stays constant without pad conditioning. These characteristics are very useful for slurry reuse. Remanufacture of Mn_{2}O_{3} slurry from used slurry has been demonstrated, and the removal rates of the remanufactured and fresh slurries are the same. Reuse and remanufacturing drastically reduce the amount of waste.

Comprehensive Study of the X-Ray Photoelectron Spectroscopy Peak Shift of La-Incorporated Hf Oxide for Gate Dielectrics

2012-04-03T09:00:00+09:00

Authors: Takashi Yamamoto, Shingo Ogawa, Jun-ichi Tsuji, Koji Kita, Katsunori Tagami, Tsuyoshi Uda, Takuji Hosoi, Takayoshi Shimura, and Heiji Watanabe
We measured the X-ray photoelectron spectroscopy spectra of the La-incorporated Hf oxide and observed the apparent Hf 4f peak shift toward a lower energy as La concentration increased. To investigate the origin of these peak shifts, we performed first-principles calculations, in which the degree and direction of the obtained peak shifts agreed well with the above-mentioned experimentally observed spectra. Also, we found that the main reason for these peak shifts was the charge-transfer effect. Estimation of the degree of the interface dipole was made possible by a comparison between the experimental values and the theoretical values of the peak shifts.

Microscopic Structure of Stepwise Threading Dislocation in 4H-SiC Substrate

2012-04-02T09:00:00+09:00

Authors: Yukari Ishikawa, Yoshihiro Sugawara, Hiroaki Saitoh, Katsunori Danno, Hiroshi Suzuki, Takeshi Bessho, Yoichiro Kawai, and Noriyoshi Shibata
The dislocation structure that forms the caterpillar-shaped etch pit upon molten KOH etching is investigated by transmission electron microscopy employing a weak-beam dark-field method. The observed dislocation has the Burgers vector 1/3[-12-10], and its structure was transformed from a basal plane dislocation to a threading edge dislocation. In the basal plane dislocation region, it propagated parallel to the [10-10] direction. On the basis of the measured dislocation structure, the caterpillar pit formation is explained. The process of dislocation formation is discussed by analyzing the relationship between sample types and the detection of the caterpillar pits.

Unidirectional Liquid Crystal Pretilt Generation on Asymmetric Nanoscaled Groove Pattern Driven by Atomic Force Microscopic Tip

Jin Seog Gwag, Soo In Jo, You-Jin Lee, and Jae-Hoon Kim — 2012-04-02T09:00:00+09:00

Authors: Jin Seog Gwag, Soo In Jo, You-Jin Lee, and Jae-Hoon Kim
We demonstrate uniformly and unidirectionally distributed pretilt characteristics of a liquid crystal cell fabricated via a substrate with a scan-directional slant nanosized surface groove pattern driven through an atomic force microscopic (AFM) tip that is continuously modulating the contact force in the scanning line direction. The resultant electro-optic characteristics of the liquid crystal (LC) cell made by our advanced AFM lithography technique show that it generates a unidirectional pretilt that guarantees wider LC applications.

Investigation of Optical and Electrochromic Properties of Tungsten Oxide Deposited with Horizontal DC and DC Pulse Magnetron Sputtering

Hsi-Chao Chen, Der-Jun Jan, and Chien-Han Chen — 2012-04-02T09:00:00+09:00

Authors: Hsi-Chao Chen, Der-Jun Jan, and Chien-Han Chen
The proposal of this research was to compare the optical and electrochromic properties of tungsten oxide (WO_{3}) thin films deposited with a horizontal direct current (DC) and DC pulse magnetron sputtering. These WO_{3} thin films were deposited onto indium tin oxide (ITO) glass and p-type silicon substrate at different gas ratios of oxygen and argon. The variation in the transmittance between the coloring and bleaching was important for the smart window. WO_{3} thin films have good electrochromic properties at gas ratios of oxygen/argon (O_{2}/Ar) of 0.7 and 0.6 for DC and DC pulse magnetron sputtering, respectively. However, WO_{3} thin films deposited by DC pulse magnetron sputtering have better optical and electrochromic properties than the films deposited by DC magnetron sputtering.

Electrostatic Properties of Organic Monolayers on Silicon Oxides Studied by Kelvin Probe Force Microscopy

Ryota Mishima, Ngyuen Thu Loan, and Hirokazu Tada — 2012-04-02T09:00:00+09:00

Authors: Ryota Mishima, Ngyuen Thu Loan, and Hirokazu Tada
The vacuum level (VL) shifts of pentacene (PEN), perfluoro-PEN (PFP), α,ω-dihexylsexithiophene (DH-6T) and N,N-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) monolayers on SiO_{2} terminated with various chemical species were studied by Kelvin probe force microscopy (KPFM). The PEN and PFP monolayers deposited on OH– and CH_{3}–SiO_{2} showed a downward VL shift, while those on CF_{3}–SiO_{2} showed an upward VL shift. The VL shift is considered to originate not from the charge transfer but from the dipole induced in molecules by surface charges. The KPFM of the DH-6T and PTCDI-C13 monolayers on OH–SiO_{2} revealed that the alkyl chains between the π-system and SiO_{2} reduce the effect of surface charges. The structural asymmetry of these molecules causes the VL shift.

Evaluation and Control of Break-Even Time of Nonvolatile Static Random Access Memory Based on Spin-Transistor Architecture with Spin-Transfer-Torque Magnetic Tunnel Junctions

Yusuke Shuto, Shuu’ichirou Yamamoto, and Satoshi Sugahara — 2012-03-30T09:00:00+09:00

Authors: Yusuke Shuto, Shuu’ichirou Yamamoto, and Satoshi Sugahara
The energy performance of a nonvolatile static random access memory (NV-SRAM) cell for power gating applications was quantitatively analyzed for the first time using the performance index of break-even time (BET). The NV-SRAM cell is based on spin-transistor architecture using ordinary metal–oxide–semiconductor field-effect transistors (MOSFETs) and spin-transfer-torque magnetic tunnel junctions (STT-MTJs), whose circuit representation of spin-transistor is referred to as a pseudo-spin-MOSFET (PS-MOSFET). The cell is configured with a standard six-transistor SRAM cell and two PS-MOSFETs. The NV-SRAM cell basically has a short BET of submicroseconds. Although the write (store) operation to the STT-MTJs causes an increase in the BET, it can be successfully reduced by the proposed power-aware bias-control for the PS-MOSFETs.

Dielectric Properties of Y_{2}O_{3} and Nb_{2}O_{5} Co-Doped Barium Titanate Ceramics

Wan Q. Cao, Fang L. Li, Mukhlis M. Ismail, and Gang Xiong — 2012-03-30T09:00:00+09:00

Authors: Wan Q. Cao, Fang L. Li, Mukhlis M. Ismail, and Gang Xiong
Conventional solid-state route method was used to prepare barium titanate ceramics doped with Y_{2}O_{3} and Nb_{2}O_{5}, Ba(Y_{0.5}Nb_{0.5})_{x}Ti_{(1-x)}O_{3} (x = 0.02, 0.04, 0.06, 0.08). The X-ray diffraction results confirmed that Y^{3+} and Nb^{5+} both substitute for Ti^{4+} at the B-site of ABO_{3} perovskite type structure, and second phase appeared for x = 0.04 and 0.06. With the increases of Y^{3+} and Nb^{5+} concentrations, peak of dielectric constant of Ba(Y_{0.5}Nb_{0.5})_{x}Ti_{(1-x)}O_{3} ceramics shifts to lower temperature more rapidly than that of BaZr_{x}Ti_{1-x}O_{3} ceramics as the same x content. It was found that Ba(Y_{0.5}Nb_{0.5})_{0.06}Ti_{0.94}O_{3} ceramics has compact structure, better temperature stability of dielectric constant, larger dielectric tunability under DC electric field. The results showed that, the Y_{2}O_{3} and Nb_{2}O_{5} doping improved the figure of merit for the BaTiO_{3} ceramics.

AC Power Consumption of Single-Walled Carbon Nanotube Interconnects: Non-Equilibrium Green's Function Simulation

Takahiro Yamamoto, Kenji Sasaoka, and Satoshi Watanabe — 2012-03-30T09:00:00+09:00

Authors: Takahiro Yamamoto, Kenji Sasaoka, and Satoshi Watanabe
We theoretically investigate the emittance and dynamic dissipation of a nanoscale interconnect consisting of a metallic single-walled carbon nanotube using the non-equilibrium Green's function technique for AC electronic transport. We show that the emittance and dynamic dissipation depend strongly on the contact conditions of the interconnect and that the power consumption can be reduced by adjusting the contact conditions. We propose an appropriate condition of contact that yields a high power factor and low apparent power.

Characterization of Interfaces between HfO_{2} Thin Film and Metal Electrode with Pre–Post Treatments

Young-Nam Kim — 2012-03-30T09:00:00+09:00

Authors: Young-Nam Kim
We investigated the effects of post O_{3} feeding treatment and pre–post O_{2} plasma treatment on HfO_{2} dielectric films in the metal/insulator/metal (MIM) structure TiN/HfO_{2}/TiN. The carbon contents of the HfO_{2} films decreases with increasing O_{3} feeding time, which leads to the improvement in leakage current. The O_{2} plasma and O_{3} feeding treatments produce Hf–Hf bonds in the bulk HfO_{2} film and a Ti oxide layer at the film/bottom electrode and HfO_{2}/TiN interface, which prevent the out diffusion of nitrogen into the HfO_{2} layer. In addition, these treatments also create the local crystallization of HfO_{2} at the interface. In the case of rapid thermal annealing of an actual dynamic random access memory (DRAM) structure, TiN/HfO_{2}/Al_{2}O_{3}/HfO_{2}/TiN, a local crystallization is also observed in the HfO_{2} layer, which enhances leakage current.

Fabrication and Electrical Properties of Thermally Oxidized p-Channel Metal–Oxide–Semiconductor Field-Effect Transistors on 4H-SiC C-Face

Mitsuo Okamoto, Miwako Iijima, Kenji Fukuda, and Hajime Okumura — 2012-03-30T09:00:00+09:00

Authors: Mitsuo Okamoto, Miwako Iijima, Kenji Fukuda, and Hajime Okumura
We characterized the SiO_{2}/SiC interface by capacitance–voltage (C–V) measurement in order to obtain p-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) on the 4H-SiC(000-1) C-face. Wet gate oxidation was preferable for both n- and p-type MOS capacitors, but p-type MOS interface properties were inferior to those of n-type MOS capacitors. The cause of the large flat-band shift for the p-type sample was discussed on the basis of C–V measurements by the light illumination technique. We also investigated the influence of the high-temperature annealing process after gate oxidation on the MOS interface properties. The p-type MOS interface was more sensitive to the annealing process than the n-type MOS interface. We fabricated 4H-SiC C-face p-channel MOSFETs by wet gate oxidation and low-temperature postdeposition annealing in He–H_{2} ambient. The normal FET operation was accomplished on the 4H-SiC C-face for the first time. Those devices, however, indicated low channel mobility and large threshold voltage.

Organic Field-Effect-Transistor-Based Memory with Nylon 11 as Gate Dielectric

Heisuke Sakai, Hayato Isoda, and Yukio Furukawa — 2012-03-29T09:00:00+09:00

Authors: Heisuke Sakai, Hayato Isoda, and Yukio Furukawa
We present the electrical properties of an organic memory device based on an organic field-effect transistor using a thin film of nylon 11 as a gate dielectric. The transfer characteristics of the memory device showed large hysteresis. A large shift of 37 V in the transfer characteristics was obtained by the application of a writing bias to the gate dielectric. The drain current ratio of the on-state to off-state was ca. 100. The on-state of the memory device showed a clear memory characteristic.

A Compact 2 Degree-of-Freedom Energy Harvester with Cut-Out Cantilever Beam

Hao Wu, Lihua Tang, Yaowen Yang, and Chee Kiong Soh — 2012-03-29T09:00:00+09:00

Authors: Hao Wu, Lihua Tang, Yaowen Yang, and Chee Kiong Soh
In this work, a novel 2 degree-of-freedom (DOF) vibration energy harvester is proposed. The harvester comprises one main cantilever beam and one secondary cantilever beam cut out within the main beam. By varying the proof masses, the first two resonances can be tuned close to each other, while maintaining significant magnitudes, thus providing a useful wide bandwidth for energy harvesting. Unlike previous 2-DOF harvesters, the proposed harvester is compact and utilizes the beam more efficiently by generating energy from both the main and secondary cantilevers. Therefore, the proposed harvester is more adaptive and functional in practical random or frequency-variant vibrational circumstances.

Analyzing Photo Induced Internal Electric Field in Pentacene/C_{60} Double-Layer Organic Solar Cells under Various External Voltages by Electric-Field-Induced Optical Second Harmonic Generation Measurement

Xiangyu Chen, Dai Taguchi, Martin Weis, Takaaki Manaka, and Mitsumasa Iwamoto — 2012-03-29T09:00:00+09:00

Authors: Xiangyu Chen, Dai Taguchi, Martin Weis, Takaaki Manaka, and Mitsumasa Iwamoto
By using electric-field-induced optical second-harmonic generation (EFISHG) measurement, we investigated interfacial carrier behavior in pentacene/C_{60} double-layer organic solar cells (OSCs). At various external DC biasing conditions, photoinduced electric field in the OSCs was directly probed by the EFISHG measurements. A potential drop was generated by photoillumination, in a manner like a potential difference across an external resistance, while applying an external DC voltage to the OSCs enables us to examine the carrier behaviors over the entire region of the external voltage V_{ex}. Results showed that only organic double-layer interface charging was induced under positive DC biasing by photoillumination, while interface and electrode charging were induced under negative DC biasing. Analyzing the pentacene/C_{60} double layer OSCs based on a Maxwell–Wagner model, we showed that the dielectric nature of the organic layers was responsible for the asymmetric charging processes.

Effect of Seed Layer on Room Temperature Tunnel Magnetoresistance of MgO Barriers Formed by Radical Oxidation in IrMn-Based Magnetic Tunnel Junctions

Faiz Dahmani — 2012-03-29T09:00:00+09:00

Authors: Faiz Dahmani
NiFe-seeded magnetic tunnel junctions (MTJs) of IrMn/CoFe/MgO/CoFeB were successfully formed by radically oxidizing a thin Mg layer. Room temperature (RT) tunnel magnetoresistance (TMR) of up to 211±10% was obtained and found to be strongly dependent on the thickness of the NiFe seed layer. High resolution transmission microscopy (HRTEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and magneto-optic Kerr effect (MOKE) analyses performed on NiFe/IrMn bilayer systems revealed that the IrMn(111)-fcc texture, grain size, surface roughness (rms), and exchange-biasing field (H_{ex}) were strongly affected by the thickness of the NiFe seed layer. A critical NiFe thickness (t_{c} ≈12 Å) was found: For t_{NiFe}≤t_{c}, the IrMn showed a very poor (111)-fcc texture with reduced grain size, very smooth surface, and reduced H_{ex}. For t_{NiFe} > t_{c}, the IrMn showed a complete opposite behavior: much enhanced (111)-fcc texture with larger grain size, rougher surface, and larger H_{ex}. For MTJ-based IrMn systems, a striking behavior is reported: larger TMRs and lower tunnel junction resistance (RA) products are obtained for t_{NiFe} ≤t_{c} while lower TMRs and larger RAs are obtained for t_{NiFe} > t_{c}.

Analysis of the Influence of Sputtering Damage to Polymer Gate Insulators in Amorphous InGaZnO_{4} Thin-Film Transistors

2012-03-29T09:00:00+09:00

Authors: Mitsuru Nakata, Hiroto Sato, Yoshiki Nakajima, Hiroshi Tsuji, Yoshihide Fujisaki, Tatsuya Takei, Toshihiro Yamamoto, and Hideo Fujikake
We have fabricated InGaZnO_{4} (IGZO) thin-film transistors (TFTs) with olefin-type polymer gate insulators formed at 130 °C and compared the transfer characteristics of top- and bottom-gate structures. We have investigated the mechanism behind the differences in the characteristics, focusing on the influence of IGZO sputtering damage to the polymer insulators. Bottom-gate IGZO-TFTs showed significant threshold voltage decreases attributable to positive fixed charges in the polymer gate insulators. These charges were generated by diffused metal ions during IGZO sputtering. Contrastingly, there was no sputtering damage to the polymer gate insulators in top-gate IGZO-TFTs, and these showed good switching performance.

Development of a Compact Moving-Sample Magnetometer Using High-T_{c} Superconducting Quantum Interference Device

2012-03-29T09:00:00+09:00

Authors: Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Akira Tsukamoto, Seiji Adachi, Keiichi Tanabe, Akihiko Kandori, and Keiji Tsukada
We developed a compact moving-sample magnetometer that uses a high-temperature superconductor–superconducting quantum interference device (high-T_{c} SQUID) to directly measure the flux coupled to a normal detection coil from a sample's magnetic moment in the presence of an external DC magnetic field. The moving-sample method is employed by inserting the sample between the poles of a DC electromagnet and vibrating the sample along the axis perpendicular to the external field axis using an actuator at a frequency of 2.693 Hz. First, the magnetic field of the sample is transferred by a first-order differential normal Cu coil to a SQUID for detection. Then, the SQUID output is fed to a lock-in amplifier for detection. The critical feature of the system design is the use of high-T_{c} SQUID, which enables the realization of a compact system. The basic characteristics of the developed system are presented, and the current system exhibited a detection limit of 1×10^{-7} emu.

Ta_{2}O_{5} Polycrystalline Silicon Capacitors with CF_{4} Plasma Treatment

Chyuan-Haur Kao and Hsiang Chen — 2012-03-28T09:00:00+09:00

Authors: Chyuan-Haur Kao and Hsiang Chen
In this research, the effects of CF_{4} plasma treatment with post annealing on the electrical characteristics and material properties of Ta_{2}O_{5} dielectrics were determined. The dielectric performance characteristics of samples under different treatment conditions were measured using equivalent oxide thickness (EOT), current density–electric field (J–E) characteristics, gate voltage shift versus time, and Weibull plots. In addition, X-ray diffraction (XRD) analysis provided insight into the changes in crystalline structure, atomic force microscopy (AFM) measurements visualized the surface roughness, and secondary ion mass spectroscopy (SIMS) revealed the distribution of fluorine ions inside the dielectric samples. Findings indicate that dielectric performance can be significantly improved by CF_{4} plasma treatment for 1 min with post annealing at 800 °C. The improvements in electrical characteristics were caused by the appropriate incorporation of the fluorine atoms and the removal of the dangling bonds and traps. The Ta_{2}O_{5} dielectric incorporated with appropriate CF_{4} plasma and annealing treatments shows great promise for future generation of nonvolatile memory applications.

Fabrication of Piezoelectric Polyurea Films by Alternating Deposition

Takashi Yanase, Tetsuya Hasegawa, Taro Nagahama, and Toshihiro Shimada — 2012-03-28T09:00:00+09:00

Authors: Takashi Yanase, Tetsuya Hasegawa, Taro Nagahama, and Toshihiro Shimada
We demonstrate that polyurea films can be prepared by alternating deposition with automated deposition control involving quartz crystal microbalance monitoring and optical source heating. The thickness of the films was linearly controlled by changing the repetition time of deposition, and the stoichiometry obtained was much higher than ±5%. The surface roughness of a 600-nm-thick film was 0.5 nm, which ensures the nm thickness control of the deposited polymers. The piezoelectricity of the films was confirmed by directly measuring the current transient induced by mechanical stress and by measuring the capacitance change induced by electric field.

Improved Device Lifetime of Organic Light Emitting Diodes with an Electrochemically Stable π-Conjugated Liquid Host in the Liquid Emitting Layer

2012-03-28T09:00:00+09:00

Authors: Shuzo Hirata, Hyo Jung Heo, Yuki Shibano, Osamu Hirata, Masayuki Yahiro, and Chihaya Adachi
The device lifetimes of organic light emitting diodes with a liquid emitting layer (liquid OLEDs) were improved by proper combination of host and guest molecules in the liquid emitting layer. The device lifetime strongly depends on the electrochemical stability of radical cations in the liquid emitting layer. The electrochemical stability of the liquid host materials was achieved by the dimerization of the alkyl-substituted carbazole 9,9'-2-[2-(2-methoxyethoxy)ethoxy]ethyl-3,3'-bis(9H-carbazole) [(TEGCz)_{2}]. The use of a guest compound with its highest occupied molecular orbital level higher in energy than that of (TEGCz)_{2} is a critical factor for realizing stable electroluminescence performance. A liquid OLED with proper combination of the guest and host materials showed an improved device lifetime of longer than 1 h, which is 100 times longer than that of our previous reports.

Fundamental Properties of Novel Design Microstrip Line Type of Liquid Crystal Phase Shifter in Microwave Region

2012-03-28T09:00:00+09:00

Authors: Ryouta Ito, Takayuki Kawakami, Yusuke Ito, Takayuki Sasamori, Yoji Isota, Michinori Honma, and Toshiaki Nose
A planar-type electrically tunable phase shifter is demonstrated in the microwave region by using liquid crystal (LC) materials. A novel planar waveguide structure based on the microstrip line, which can convert the normal microstrip line to the inverted one, is designed. The new conversion circuit enables us to introduce LC materials on the microstrip line as easily as in the case of using the coplanar waveguide type of liquid crystal phase shifters. Larger phase shifting properties are confirmed empirically up to approximately 10 GHz with the application of a driving voltage of less than 10 V.

On-Chip High-Resolution Beam Scanner Based on Bragg Reflector Slow-Light Waveguide Amplifier and Tunable Micro-Electro-Mechanical System Vertical Cavity Surface Emitting Laser

Masanori Nakahama, Xiaodong Gu, Toshikazu Shimada, and Fumio Koyama — 2012-03-27T09:00:00+09:00

Authors: Masanori Nakahama, Xiaodong Gu, Toshikazu Shimada, and Fumio Koyama
We propose a monolithic beam scanner consisting of a Bragg reflector slow-light waveguide amplifier and a tunable micro-electro-mechanical vertical cavity surface emitting laser. Continuous beam steering of over 30° and a narrow divergence angle of below 0.1° are predicted, which gives us a number of resolution points over 300. In addition, the modeling on saturation characteristics of a slow light amplifier shows a possibility of the maximum output power of over 10 mW.

Giant Wavelength–Temperature Dependence of a Micro Machined Vertical Cavity Surface Emitting Laser with a Thermally Actuated Cantilever Structure

2012-03-27T09:00:00+09:00

Authors: Masanori Nakahama, Hayato Sano, Norihiko Nakata, Akihiro Matsutani, and Fumio Koyama
We present the modeling and the experimental result of a micro machined vertical cavity surface emitting laser with a thermally actuated semiconductor/SiO_{2} cantilever structure. The modeling result shows a giant wavelength–temperature dependence of over 3.5 nm/K. The fabricated device exhibits a temperature dependence of 0.79 nm/K, which is 10 times larger than that of conventional vertical cavity surface emitting lasers (VCSELs).

Effects of Electron Current and Hole Current on Dielectric Breakdown in HfSiON Gate Stacks

2012-03-27T09:00:00+09:00

Authors: Izumi Hirano, Takeshi Yamaguchi, Yasushi Nakasaki, Ryosuke Iijima, Katsuyuki Sekine, Mariko Takayanagi, Kazuhiro Eguchi, and Yuichiro Mitani
The roles of electrons and holes in the dielectric breakdown of HfSiON have been investigated by controlling the numbers of injected hot electrons and hot holes separately by the substrate hot-carrier injection technique. It has been clarified that carrier flux has the strongest effect on the dielectric breakdown of HfSiON rather than carrier energy and the electric field across dielectrics. The amount of electron flux leading to the dielectric breakdown of HfSiON is about twice as large as that of hole flux.

Theoretical Investigation of Chemical Spin Doping into Single Porphyrin Junctions toward Ultrahigh-Sensitive Nitric Oxide Sensor

Kenji Toyoda — 2012-03-27T09:00:00+09:00

Authors: Kenji Toyoda
We theoretically study chemical spin doping into single porphyrins connected to nanoelectrodes via benzenethiols, ethynyl-benzenethiols, and vinyl-benzenethiols using the adsorption of a nitric oxide (NO) molecule. For all three anchoring groups, the adsorption of a NO molecule injects one spin into single-molecule junctions and produces antiferromagnetic interactions between the injected spin and the original spins at the junctions, resulting in a decrease in the spin-polarized currents. We found that the magnitude of change in the spin-polarized current significantly depends on the type of anchoring groups; the magnitude is ordered by the following anchoring group: vinyl-benzenethiol > ethynyl-benzenethiol > benzenethiol. In particular, for vinyl-benzenethiol, spin doping causes not only π electron localization on molecular orbitals but also structural change.

Nanoimprint Mold for 2.5 Tbit/in.^{2} Directed Self-Assembly Bit Patterned Media with Phase Servo Pattern

2012-03-27T09:00:00+09:00

Authors: Ryousuke Yamamoto, Akiko Yuzawa, Takuya Shimada, Yasuaki Ootera, Yoshiyuki Kamata, Naoko Kihara, and Akira Kikitsu
We demonstrate the mold fabrication and replication process for the production of 0.8 and 2.5 Tbit/in.^{2} directed self-assembly bit patterned media (DSA-BPM). These devices are fabricated with 33 and 17 nm dot pitch patterns using the microphase segregation structure of polystyrene–poly(dimethylsiloxane) as an etching mask template. The self-assembled dot arrays are simultaneously ordered on both the circular tracks for the data area and the arbitrary marks for the servo area by DSA using groove guides. We fabricated the Si mold with dot pillars of 19.3 nm height for the 2.5 Tbit/in.^{2} DSA-BPM from the poly(dimethylsiloxane) dot mask. We also demonstrated the nickel mold replication of the 0.8 Tbit/in.^{2} DSA-BPM by electroforming from the Si mold.

Shottky Barrier Diodes on AlN Free-Standing Substrates

2012-03-26T09:00:00+09:00

Authors: Yoshihiro Irokawa, Encarnación A. García Víllora, and Kiyoshi Shimamura
Lateral Schottky rectifiers were fabricated on bulk single-crystal free-standing AlN substrates. The unintentionally doped substrates display n-type conductivity. The diode shows a low reverse leakage current of ∼0.1 nA at -40 V at room temperature. The ideality factor for forward characteristics is 11.7 at room temperature and shows temperature dependence, suggesting the lateral nonuniformities at the metal/semiconductor interface. The fabricated devices are stably operated even at 573 K, owing to the wide band gap (6.2 eV) of AlN. The reverse leakage current of the device is explained by either a trap-assisted tunneling process or one-dimensional variable-range-hopping conduction along the dislocations.

Successful Growth of Conductive Highly Crystalline Sn-Doped α-Ga_{2}O_{3} Thin Films by Fine-Channel Mist Chemical Vapor Deposition

Toshiyuki Kawaharamura, Giang T. Dang, and Mamoru Furuta — 2012-03-26T09:00:00+09:00

Authors: Toshiyuki Kawaharamura, Giang T. Dang, and Mamoru Furuta
Highly crystalline α-phase gallium oxide (Ga_{2}O_{3}) thin films were grown by fine-channel mist chemical vapor deposition on c-sapphire substrates at 400 °C at a deposition rate of more than 20 nm/min. The thin films were doped with Sn(IV) atoms, which were obtained from Sn(II) chloride by the reaction SnCl_{2}+ H_{2}O_{2}+ 2HCl→SnCl_{4}+ 2H_{2}O. Conductive α-phase Ga_{2}O_{3} thin films were successfully grown from source solutions containing less than 10 at. % Sn(IV). The source solution containing 4 at. % Sn(IV) resulted in obtaining a thin film with an n-type conductivity as high as 0.28 S cm^{-1}, a mobility of 0.23 cm^{2} V^{-1} s^{-1}, a carrier concentration of 7×10^{18} cm^{-3}, and a full width at half maximum (FWHM) of the (0006) reflection X-ray rocking curve as low as 64 arcsec.

Light Trapping by Ag Nanoparticles Chemically Assembled inside Thin-Film Hydrogenated Microcrystalline Si Solar Cells

Hidenori Mizuno, Hitoshi Sai, Koji Matsubara, and Michio Kondo — 2012-03-26T09:00:00+09:00

Authors: Hidenori Mizuno, Hitoshi Sai, Koji Matsubara, and Michio Kondo
A systematic study on the Ag nanoparticle (NP)-mediated light trapping in thin film hydrogenated microcrystalline Si (µc-Si:H) solar cells is described. In this study, a unique wet-chemical approach was applied to allow the assembly of light scattering Ag NPs inside the rear ZnO:Ga layer of µc-Si:H solar cells in a controlled manner. It was confirmed that both the surface coverage by the Ag NPs and the location of the Ag NPs in the ZnO:Ga layer have significant impacts on the final light trapping effect. By optimizing these two parameters, a 75% higher current density generated in the near-infrared range (700–1100 nm) was achieved in a Ag NP-incorporated cell compared with a cell without the Ag NP incorporation.

Effect of DC Pre-Discharge on the Generation of Atmospheric Pulsed Microdischarges

Jun Kikuchi, Yuta Suzuki, Takaaki Muto, Shinji Ibuka, and Shozo Ishii — 2012-03-26T09:00:00+09:00

Authors: Jun Kikuchi, Yuta Suzuki, Takaaki Muto, Shinji Ibuka, and Shozo Ishii
More than 2.5 kV pulsed voltages were required to obtain atmospheric pulsed microdischarges at a gap separation of more than 1.0 mm. We have developed a DC pre-discharge method for decreasing the amplitude of the repetitive pulsed voltages in the generation of atmospheric pulsed microdischarges using a miniature helium gas flow. The electrode configuration consisted of three electrodes: a nozzle, a hollow electrode with a hole having a diameter of 0.6 mm, and a plain plate. The hollow electrode separated the DC glow pre-discharge from pulsed discharges, which was the main discharge. Between the nozzle and hollow electrodes, the DC glow pre-discharge formed active particles, which were provided to the gap separation between the hollow and plate electrodes by the helium gas flow through the hollow electrode. The active particles supplied with the helium gas decreased the breakdown voltage of the pulsed microdischarges. The mode of the pulsed microdischarges was controlled by the polarity of the pulsed voltages applied to the plate electrode as the pulsed arc and glow microdischarges were obtained by positive and negative pulsed voltages, respectively. In addition to the glow pre-discharge, we were able to use the corona pre-discharge, which was generated by increasing the hole diameter of the hollow electrode to 1.2 mm. Although the breakdown voltage increased with the transition from the glow to corona pre-discharge, it was effective in reducing the power consumption of the pre-discharge, as compared with the glow pre-discharge.

Quenching Effect, Signal to Noise, Contrast to Noise Ratios on Scintillator Screens for Proton Beam Dosimetry System

2012-03-26T09:00:00+09:00

Authors: Seonkyu Kim, Se Byeong Lee, Seung Hoon Yoo, Sungkoo Cho, Dong Wook Kim, Dongho Shin, Sung Yong Park, Chan Hyeong Kim, and Sang Hoon Lee
There has been dosimetry using scintillator screen for proton quality assurance recently. To develop a proton beam dosimetry system using scintillator, we evaluated the dosimetric properties and imaging quality for three kinds of scintillator screens. Proton beam ranges of 6, 9, and 12 g/cm^{2} were determined in a water phantom using an ion chamber. Beam current was optimized about each scintillator screen at proton beam ranges of 6, 9, and 12 g/cm^{2}. Dose rate was in beam condition of proton treatment. For comparison of the dosimetric properties, the quenching correction factors and standard deviations for the scintillator screens (C_{6}H_{6}, Gd_{2}O_{2}S:Tb, and Gd_{2}O_{2}S) were obtained using the relation between the light yield (scintillator-relative output) and the dose distribution (diode-relative output). The image qualities for the scintillator screens were compared, using the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR), in consideration of the physical properties of the scintillator materials. After correction of the quenching effect, the correction factor for scintillator screen Gd_{2}O_{2}S:Tb was the lowest, at 0.004 g/(cm^{2} MeV). The standard deviations of the difference between the yields measured by the scintillator screens and the diode detector averaged 1, 1.3, and 1.3, respectively, at all of the ranges from origin to the peak position. The dosimetric properties of scintillator screens were no large difference. The SNRs of the scintillator screens (C_{6}H_{6}, Gd_{2}O_{2}S:Tb, and Gd_{2}O_{2}S) averaged 28.67, 40.18, and 24.56, respectively, at all ranges. The CNRs of the scintillator screens (C_{6}H_{6}, Gd_{2}O_{2}S:Tb, and Gd_{2}O_{2}S) averaged 0.44, 0.33, and 0.42, respectively, at all ranges. The highest SNR and the lowest CNR of scintillator screen Gd_{2}O_{2}S:Tb were more excellent than those of the other scintillator screens. We evaluated the dosimetric properties in terms of the quenching-effect correction factors, standard deviations image qualities in terms of SNR and CNR about scintillator screens. The correction factor and standard deviation for scintillator screens made no large difference. Scintillator screen Gd_{2}O_{2}S:Tb had the highest value of SNR and the lowest value of CNR, and accordingly was considered to be best in proton beam imaging quality.

Mean Transverse Energy Measurement of Negative Electron Affinity GaAs-Based Photocathode

2012-03-26T09:00:00+09:00

Authors: Shunya Matsuba, Yosuke Honda, Xiuguang Jin, Tsukasa Miyajima, Masahiro Yamamoto, Takashi Uchiyama, Makoto Kuwahara, and Yoshikazu Takeda
A negative electron affinity GaAs photocathode electron source is characterized by high brightness, high quantum efficiency, and a moderate temporal response. The initial emittance depends on the mean transverse energy (MTE) of the electrons on the cathode surface. We evaluated the MTE based on emittance measurements obtained using the waist scan method with three types of cathodes: bulk GaAs, thickness-controlled samples with active-layer thicknesses of 100 and 1000 nm, and a GaAs/GaAsP superlattice sample. The dependence of the cathode quantum efficiency, the laser wavelength, and the thickness of the GaAs cathode active layer on the MTE are described. In the case of the bulk GaAs and the thickness-controlled samples, it was determined that the thickness and cathode quantum efficiency do not affect the MTE within the measurement error. The laser wavelength, on the other hand, affects the MTE of all cathodes.

Oxidation of Silicon Utilizing a Microwave Plasma System: Electric-Stress Hardening of SiO_{2} Films by Controlling the Surface and Interface Roughness

Yoshiro Kabe, Ryu Hasunuma, and Kikuo Yamabe — 2012-03-23T09:00:00+09:00

Authors: Yoshiro Kabe, Ryu Hasunuma, and Kikuo Yamabe
Electric-stress hardening of silicon dioxide (SiO_{2}) films under high electric field stresses was studied. SiO_{2} films were formed by two-step oxidation utilizing thermal oxidation and plasma oxidation. This process has the advantages of both oxidation processes: the low degradation rate of thermal oxidation and the flat SiO_{2} surface and SiO_{2}/Si interface obtained by plasma oxidation. Time-dependent dielectric breakdown and stress-induced leakage current were measured to evaluate the degradation rate and the breakdown lifetime of the oxides. Atomic force microscopy was used to evaluate the roughnesses of the SiO_{2} surface and interface. The two-dimensional degradation distribution under a current stress was investigated by the stress-induced etched-oxide surface roughness method. Atomically uniform SiO_{2} was found to suppress the generation of local weak spots under current stress. We conclude that using an appropriate combination of the oxidation processes can reduce the degradation and enhance the breakdown lifetimes of SiO_{2} films.

Space Charge Trapping and Conduction in Low-Density Polyethylene/Silica Nanocomposite

Jiandong Wu, Yi Yin, Li Lan, Qiaohua Wang, Xuguang Li, and Dengming Xiao — 2012-03-23T09:00:00+09:00

Authors: Jiandong Wu, Yi Yin, Li Lan, Qiaohua Wang, Xuguang Li, and Dengming Xiao
The high field conduction and space charge distribution were investigated in low-density polyethylene (LDPE) and LDPE/silica nanocomposites filled with various concentrations of nanosilica. The results indicate that nanosilica could effectively suppress space charge accumulation at nanofiller concentrations from 0.1 to 5.0 wt %. However, the conduction current at a high field significantly increases at low concentrations from 0.1 to 0.5 wt % and remarkably reduces at high concentrations from 0.5 to 5.0 wt %. It is shown that the trap depth corresponding to the time from 2 to 3600 s significantly decreases at low nanofiller concentrations from 0.1 to 0.5 wt %. However, the depth of deep traps corresponding to the time from 100 to 3600 s increases with the increase in nanofiller concentration from 0.5 to 5.0 wt %. Moreover, the depth of shallow traps corresponding to the time from 2 to 100 s increases at concentrations from 0.5 to 2.0 wt %, and then it decreases at concentrations from 2.0 to 5.0 wt %. In addition, the apparent mobility varies with the modification of trap depth caused by the introduction of nanofiller. The threshold field E_{Ω–t} for remarkable charge injection and E_{t–c} proportional to the total trap density H are significantly lower in the nanocomposite with a low nanosilica concentration, i.e., 0.1 and 0.5 wt %, while both of them increase at concentrations from 0.5 to 5.0 wt %. It is considered that the impurity effect is greater than the nanofiller effect at a low nanofiller concentration. The deep trap is speculated as the chemical trap in the interface of the nanofiller bonding strongly with the polymer chain, while the shallow trap may be related to the chemical trap in the weakly bonded interface. It is clear that the space charge behavior and conduction are significantly affected by modification of the trap depth and density distribution owing to the introduction of nanofiller.

Effective Medium Theory for Calculating Reflectance from Metal–Dielectric Multilayered Structure

Shinji Kameda, Akio Mizutani, and Hisao Kikuta — 2012-03-23T09:00:00+09:00

Authors: Shinji Kameda, Akio Mizutani, and Hisao Kikuta
An effective medium theory (EMT) for calculating optical reflectance from a surface of metal-and-dielectric multilayered structures (MDMS) has been described. MDMS is a strongly-anisotropic optical medium of which the dispersion surface is cylindrical for transverse-magnetic (TM) polarized light. A coefficient of reflection has been derived by applying the dispersion surface of MDMS to the phase-matching condition and the boundary conditions at the interface between an isotropic medium and the MDMS. The reflectance calculated by this anisotropic effective medium theory has agreed with the results by the finite-difference time-domain (FDTD) method, even for oblique incidence. Moreover, transmittance and reflectance from a finite thick MDMS layer are also derived by using the effective medium theory.

Improvement of Electrostatic Discharge Protection by Introducing a Spindt-Type Silicon Field Emission Device

Liann-Be Chang, Yi-Cherng Ferng, Jhong-Wei Liao, and Ching-Chi Lin — 2012-03-23T09:00:00+09:00

Authors: Liann-Be Chang, Yi-Cherng Ferng, Jhong-Wei Liao, and Ching-Chi Lin
In this paper, an original Spindt-type silicon field emission device (FED) with electrostatic discharge (ESD) regulation capability is proposed. The fabricated FED characteristics, including process parameters, capacitance–voltage (C–V), current–voltage (I–V), and frequency response, are investigated. To verify its capability of ESD protection, we replace the metal oxide varistor (MOV) in a state-of-the-art protection configuration with the fabricated FED under the application conditions of system-level ESD tests. The measured results show that the proposed ESD protection circuit composed of a prestage gas arrestor, an intermediate resistor, and an introduced FED can suppress an injected ESD pulse voltage of 6000 to 3193 V, a reduction of 46.8%, whereas suppression is to 5606 V, a reduction of 6.57%, when using only a gas arrestor.

High Hole Mobility in GaAs_{1-x}Bi_{x} Alloys

Kosuke Kado, Takuma Fuyuki, Kazuya Yamada, Kunishige Oe, and Masahiro Yoshimoto — 2012-03-22T09:00:00+09:00

Authors: Kosuke Kado, Takuma Fuyuki, Kazuya Yamada, Kunishige Oe, and Masahiro Yoshimoto
A hole mobility of ∼200 cm^{2} V^{-1} s^{-1} was demonstrated for GaAs_{1-x}Bi_{x} (x ≤4%). This value is comparable to that of GaAs with the same hole concentration. The hole mobility of GaAs_{1-x}Bi_{x} (x ≈5%) degrades, but is still larger than the reported values for GaAs_{1-x}Bi_{x}. Despite concerns regarding the degradation of hole mobility in GaAs_{1-x}Bi_{x} due to scattering at Bi-related localized states near the valence band, p-type GaAs_{1-x}Bi_{x} was able to be obtained without degradation of hole mobility. This is probably owing to the surfactant effect of the bismuth atoms during growth.

Light Source Position Dependence of Evanescent Wave Coupling Effect in Narrow GaAs/AlGaAs Ridge Structure

Xue-Lun Wang and Tokio Takahashi — 2012-03-22T09:00:00+09:00

Authors: Xue-Lun Wang and Tokio Takahashi
The light source position dependence of the evanescent wave coupling effect in a sub-wavelength-sized GaAs/AlGaAs ridge structure was investigated using the theoretical simulation and temperature-dependent emission pattern measurements. It was found that the evanescent wave coupling effect could be realized for a light source located at any position of the top-flat quantum well (QWL), although the emissions transformed from evanescent waves began to get emitted in directions that formed an increasingly larger angle with respect to the surface normal of the ridge flat facet when the light source was moved from the center to the edge of the flat QWL.

An Enhanced Operational Stability of Organic Light Emitting Devices with Polymeric Buffer Layer

Sang Hee Cho and Min Chul Suh — 2012-03-22T09:00:00+09:00

Authors: Sang Hee Cho and Min Chul Suh
A uniform and robust polymer-based hole injection layer (HIL) was formed by spin-casting process in an ambient air condition. The rough surface of indium tin oxide (ITO) was covered by this polymer-based HIL which plays an important role as a buffer layer. The utilization of this buffered HIL polymer resulted in an enhanced long-term stability of organic light emitting devices (OLEDs). In addition, we found that the precise control of hole current flow is possible by doping of 9,10-dicyanoanthracene (DCA) with moderate electron affinity (∼3.5 eV) plausibly due to a strong dipole interaction with the polymeric HIL material. As a result, a new buffer layer doped with DCA showed a substantially controlled hole injection into an emitting layer (EML) which causes a much more enhanced lifetime of the blue OLED by a factor of 4.3.

Giant Field-Induced Distortion in Mn_{3}SbN at Room Temperature

Koshi Takenaka, Takashi Shibayama, Daiki Kasugai, and Takeshi Shimizu — 2012-03-22T09:00:00+09:00

Authors: Koshi Takenaka, Takashi Shibayama, Daiki Kasugai, and Takeshi Shimizu
The discovery of magnetostriction at room temperature in the antiperovskite Mn_{3}SbN is reported herein. Mn_{3}SbN undergoes a phase transition from a high-temperature (high-T) paramagnetic state to a low-T ferromagnetic (FM) state at the Curie temperature of T_{C} = 360 K, accompanied by a cubic-to-tetragonal structural deformation. In the tetragonally distorted FM phase, Mn_{3}SbN exhibits large magnetostriction of up to 450 ppm, estimated from the linear thermal expansion under a magnetic field of 90 kOe while slowly reducing the temperature. The magnetostriction estimated by the same procedure is enhanced to 1000 ppm without reduction of the operating temperature by partial replacement of the constituent elements. The present results are examined in terms of ferromagnetic shape memory effects.

Fabrication of Poly(9,9'-dioctylfluorene)-Based Nano- and Microstructures by Proton Beam Writing

2012-03-22T09:00:00+09:00

Authors: Yuta Maeyoshi, Katsuyoshi Takano, Atsushi Asano, Hiromi Marui, Masaaki Omichi, Takahiro Satoh, Tomihiro Kamiya, Yasuyuki Ishii, Takeru Ohkubo, Masashi Koka, Wataru Kada, Masaki Sugimoto, Hiroyuki Nishikawa, Akinori Saeki, and Shu Seki
A new and direct nano-microprocessing technique for poly(9,9'-dioctylfluorene) (PFO) films using proton beam writing (PBW) based on the cross-linking reaction of the polymer without a cross-linking agent was proposed. Not only the surface morphology but also structure size and shape on PFO films can be controlled from the nanometer to micrometer scale by adjusting the fluence of incident protons. Fabrication of three-dimensional PFO structures with an aspect ratio of 12 was successfully demonstrated by PBW with the adjustment of fluence at 3.5×10^{6} ions/µm^{2}.

Growth of Epitaxial Anatase TiO_{2}(001) Thin Film on NaCl(001) Substrate by Ion Beam Sputtering and Thermal Annealing

2012-03-22T09:00:00+09:00

Authors: Chung-Ho Kao, Jia-Hong Tsai, Sung-Wei Yeh, Hsing-Lu Huang, Dershin Gan, and Pouyan Shen
The anatase TiO_{2}(001) surface was shown to have superior photoreactivity. Epitaxial anatase (001) films used to be grown on single-crystal SrTiO_{3} and LaAlO_{3} substrates. It is shown in this report that these films can be grown also on the NaCl substrate, which is much cheaper and easily prepared. Epitaxial TiO(001) films were first grown on the NaCl(001) substrate. By testing the TiO-to-anatase transformation over temperature and time ranges, an epitaxial anatase (001) film was prepared by simple thermal oxidation in air. The formation of a single-variant anatase (001) film instead of a multiple-variant film is discussed in this report.

First-Principles Study on Intrinsic Point Defects in Rhombohedral LaAlO_{3} and Their Effects on Electrical Properties

Xiaojun Xie, Yonghong Cheng, Bing Xiao, and Yoshimichi Ohki — 2012-03-21T09:00:00+09:00

Authors: Xiaojun Xie, Yonghong Cheng, Bing Xiao, and Yoshimichi Ohki
Formation energies and energy levels of various neutral and charged defects in bulk rhombohedral LaAlO_{3} are calculated numerically in different equilibrium conditions under different oxygen partial pressures, using first-principles plane-wave calculations. The roles of such defects in electrical properties of LaAlO_{3} are also discussed. The results obtained by calculations show that the formation energy becomes low for oxygen interstitial if LaAlO_{3} is in an oxygen-rich condition. In contrast, an oxygen vacancy is easily formed in a condition where oxygen is deficient and metal elements are relatively rich, even if the oxygen partial pressure is high. These results explain well the concentration change of constituent elements in LaAlO_{3} under different treatment atmospheres. Furthermore, the calculations can interpret a large tunnelling current that is often observed in a metal–oxide–silicon structure using LaAlO_{3} as the oxide layer, since the O vacancy has an energy level near the valence band maximum of Si.

n-Channel Metal–Oxide–Semiconductor Field-Effect Transistor Modeling in Forward Body Bias Condition for Low Voltage Complementary Metal–Oxide–Semiconductor Circuits Design

Hitoshi Aoki and Akira Matsuzawa — 2012-03-21T09:00:00+09:00

Authors: Hitoshi Aoki and Akira Matsuzawa
This paper proposes a modified transistor model to improve the accuracy under the forward body bias operation that is vital for low voltage circuits, such as 0.5 V, to reduce the power consumption of complementary metal–oxide–semiconductor (CMOS) LSI. The proposed model and equations were implemented in BSIM4 version 4.6 with SPICE3f5 and verified by measurements of 60 nm n-channel metal–oxide–semiconductor field-effect transistors (n-MOSFETs). Approximately 50% inaccuracy of the drain current can be corrected. Furthermore, the importance of the proposed model will become higher with further lower threshold voltage operation requirements.

Acid Generation Mechanism for Extreme Ultraviolet Resists Containing Pinanediol Monosulfonate Acid Amplifiers: A Pulse Radiolysis Study

2012-03-21T09:00:00+09:00

Authors: Kazuyuki Enomoto, Koji Arimitsu, Atsutaro Yoshizawa, Ravi Joshi, Hiroki Yamamoto, Akihiro Oshima, Takahiro Kozawa, and Seiichi Tagawa
Very highly sensitive resists are required for extreme ultraviolet (EUV, 13.5 nm) lithography, which is regarded as the most promising next-generation lithography. Chemically amplified resists have been proposed to increase acid yield and sensitivity through the use of an acid amplifier. There are two steps for acid generation in chemically amplified resists: initial acid generation and acid amplification. The first systematic research on the acid generation mechanisms of chemically amplified resists showing the involvement of acid amplifiers has been performed by both time-resolved pulse radiolysis and spectrophotometric titration methods. The role of acid amplifiers in acid generation processes, initiated by exposure, has been clarified using toluene and trifluoromethylbenzene derivatives of pinanediol monosulfonate.

X-ray Photoemission Spectroscopy Study of GaAs(111)B Substrate Nitridation using an RF-Radical Source

Shigeya Naritsuka, Midori Mori, Yoshitaka Takeuchi, and Takahiro Maruyama — 2012-03-21T09:00:00+09:00

Authors: Shigeya Naritsuka, Midori Mori, Yoshitaka Takeuchi, and Takahiro Maruyama
The mechanism of GaAs(111)B surface nitridation using an RF-radical source was studied while systematically changing the nitridation temperature. Atomic force microscopy and X-ray photoemission spectroscopy measurements indicated that the nitridation of the GaAs(111)B surface showed a similar dependence on nitridation temperature to that of a GaAs(001) surface. Both the degree of nitridation and the Ga adatom density increased with increasing nitridation temperature, and above 510 °C, Ga droplets were formed. Strong photoluminescence signals were obtained from the GaAs(111)B surfaces.

The Effects of Ba-Additive on Growth of a-Plane GaN Single Crystals Using Na Flux Method

2012-03-19T09:00:00+09:00

Authors: Keiko Masumoto, Tatsuya Someno, Kosuke Murakami, Hiroki Imabayashi, Hideo Takazawa, Yuma Todoroki, Daisuke Matsuo, Akira Kitamoto, Mihoko Maruyama, Mamoru Imade, Masashi Yoshimura, Yasuo Kitaoka, Takatomo Sasaki, and Yusuke Mori
Large-area nonpolar GaN substrates with high crystallinity are necessary to improve the performance of GaN devices. Nonpolar GaN substrates of 2-in. diameter have been commercially fabricated by growing along the nonpolar direction on heterogeneous substrates. However, the crystallinity of the nonpolar GaN substrates requires improvement. Here, we grew a-plane GaN crystals using the Na flux method and investigated the effects of a Ba-additive on surface morphology and crystallinity. We found that the crystallinity of the crystals grown by the Na flux method was greatly improved compared with that of seed substrates. Moreover, the use of the Ba-additive suppressed the formation of voids that occurred during the Na flux growth without the Ba-additive. As a result, a-plane GaN crystals with high crystallinity were produced using the Na flux method with the Ba-additive.

Low-Loss GaInAsP Wire Waveguide on Si Substrate with Benzocyclobutene Adhesive Wafer Bonding for Membrane Photonic Circuits

2012-03-19T09:00:00+09:00

Authors: Jieun Lee, Yasuna Maeda, Yuki Atsumi, Yuta Takino, Nobuhiko Nishiyama, and Sigehisa Arai
Low-power and compact optical interconnects can be realized using III–V membrane photonic integrated circuits fabricated from thin InP-based films bonded to a Si wafer using benzocyclobutene (BCB) adhesive wafer bonding method. However, the conditions of the bonding and fabrication process strongly affect the propagation loss of waveguides. This study investigated the process conditions during bonding and waveguide fabrication with a view to reducing the propagation loss. It was found that clean, large GaInAsP thin films without air voids or fractures could be obtained by using an appropriate solvent volatilization time of 20–30 min at 200 °C for BCB. Furthermore, by using a resist with high dry etching resistance and an SiO_{2} mask for the etching process, the sidewall roughness of the waveguide was significantly reduced, which finally afforded a waveguide propagation loss as low as 4 dB/cm.

Electron Mobility Limited by Remote Charge Scattering in Thin (100)- and (110)-Oriented Silicon Body Double-Gated Metal–Oxide–Semiconductor Field-Effect Transistors with High-k Gate Dielectrics

Ryosuke Iijima, Lisa F. Edge, Vamsi Paruchuri, and Mariko Takayanagi — 2012-03-19T09:00:00+09:00

Authors: Ryosuke Iijima, Lisa F. Edge, Vamsi Paruchuri, and Mariko Takayanagi
We have investigated the electron mobility limited by the remote charge scattering, µ_{RCS}, in the thin silicon body (≤8 nm) double-gated metal–oxide–semiconductor field-effect transistors (MOSFETs), focusing on its dependency on the body thickness and the silicon surface orientation. In order to predict the µ_{RCS} in such an unprecedented MOSFET system, the adequacy of physical models used in the computation was verified by comparing the computational results with the experimentally determined µ_{RCS} from the actual bulk MOSFETs with high-k dielectric fabricated on the (100) and (110) silicon substrates. It has been discovered for the first time that the µ_{RCS} is dropped to less than half of the bulk device's µ_{RCS} when the body thickness is 5 nm and that the µ_{RCS} lowering derived from the body thickness reduction is more serious in the (110)-oriented surface than in the (100)-oriented surface. These mobility trends have been quantitatively explained by the effective mass difference between the two surfaces as well as by the carrier confinement in the metallurgically defined narrow silicon body. These observations indicate the great importance of the systematic reduction of charged traps in high-k gate dielectrics in the advanced devices.

The Static Electricity Resistant Liquid Crystal Display Driven by Fringe Electric Field

Mi Sook Kim, Seung Min Seen, and Seung Hee Lee — 2012-03-19T09:00:00+09:00

Authors: Mi Sook Kim, Seung Min Seen, and Seung Hee Lee
In this paper, we propose the static electricity resistant liquid crystal display (LCD) driven by fringe electric field. In the device, the conductive Cr metal playing role as black matrix (BM) in the top glass substrate is connected to the common electrode on the bottom substrate by the Ag transfer dotting. In addition, the common electrode also contacts to border chassis, allowing it to serve as the path for discharging the static charge generated on the top glass surface when peeling off the protective layer of the polarizer. Therefore, the electrostatic charges near BM or in the active region move fast enough to the CrBM for neutralization, while keeping the display in the neutral state electrically. The proposed LCD utilizes a liquid crystal mixture with negative dielectric anisotropy, allowing the device to be in much stable state against noise field generated by CrBM or external electrostatic discharge (ESD). We expect that this proposed structure is suitable to electrostatic resistant fringe-field switching (FFS)-LCD with a high image quality.

Observation of Fine Lung Structure by Ultrahigh-Resolution Optical Coherence Tomography Using 800, 1060, and 1300 nm Supercontinua

2012-03-19T09:00:00+09:00

Authors: Shutaro Ishida, Norihiko Nishizawa, Masashi Kitatsuji, Hiroyoshi Ohshima, Yoshinori Hasegawa, Miyoko Matsushima, and Tsutomu Kawabe
Cross-sectional imaging of isolated rat lungs was demonstrated by ultrahigh-resolution optical coherence tomography using supercontinua at 800, 1060, and 1300 nm wavelengths. The detailed structure of the trachea, including cartilage, mucosa, and annular ligaments, were observed clearly. In the imaging of visceral pleura and alveoli, when phosphate-buffered saline was instilled into the lung, the penetration depth of imaging was improved, and clear images of the fine structure of the lung, including alveoli, were observed owing to the index-matching effect. The wavelength dependence of the light source was discussed for the observation of fine structure and imaging contrast.

Determination of Anisotropic Diamagnetic Susceptibility Using X-ray Diffraction

2012-03-16T09:00:00+09:00

Authors: Tsunehisa Kimura, Guangjie Song, Kenji Matsumoto, Keiji Fujita, and Fumiko Kimura
We present a facile method for determining the anisotropic diamagnetic susceptibility of biaxial crystals by performing X-ray diffraction measurements. The proposed method is based on the fact that the amplitude of fluctuations in a crystallographic axis under a magnetic field depends on the direction of the field with respect to the susceptibility axes. By calculating the magnetic energies of a crystal under static and rotating magnetic fields, we determined the relationship of the half-width of the diffraction spots corresponding to the (hkl) planes with the anisotropic magnetic susceptibilities χ_{1}-χ_{2} and χ_{2}-χ_{3} for the static field and χ_{1}-χ_{2} and χ_{1}-χ_{3} for the rotating field, where χ_{1} > χ_{2} > χ_{3}. We have shown that the absolute values of the anisotropic diamagnetic susceptibilities can be determined if the size of the microcrystals is known, whereas only the ratio (χ_{2}-χ_{3})/(χ_{1}-χ_{2}) or (χ_{1}-χ_{3})/(χ_{1}-χ_{2}) can be determined if the microcrystal size is unknown.

Bipolar Resistive Switching Behavior of a Pt/NiO/TiN Device for Nonvolatile Memory Applications

2012-03-16T09:00:00+09:00

Authors: Tae-Geun Seong, Mi-Ri Joung, Jong-Woo Sun, Min Kyu Yang, Jeon-Kook Lee, Ji Won Moon, Jaesung Roh, and Sahn Nahm
Bipolar resistive switching behavior was observed in a Pt/NiO/TiN device. The device exhibited switching behavior that was stable over 100 cycles and did not degrade after 10^{4} s. An electroforming process was required to obtain these bipolar resistive switching properties, and the conduction behavior of the low resistance state followed Ohm's law, indicating that conductive filaments formed during the electroforming process. The conductive filaments consisted of oxygen vacancies and the Pt electrode behaved as an oxygen reservoir. The bipolar resistive switching of the Pt/NiO/TiN device was explained by the generation and annihilation of oxygen vacancies in the filaments.

Improvement of Removal Rate in Abrasive-Free Planarization of 4H-SiC Substrates Using Catalytic Platinum and Hydrofluoric Acid

2012-03-16T09:00:00+09:00

Authors: Takeshi Okamoto, Yasuhisa Sano, Kazuma Tachibana, Bui Van Pho, Kenta Arima, Kouji Inagaki, Keita Yagi, Junji Murata, Shun Sadakuni, Hiroya Asano, Ai Isohashi, and Kazuto Yamauchi
We used catalyst-referred etching, which is an abrasive-free planarization method, to produce an extremely smooth surface on a 4H-SiC substrate. However, the removal rate was lower than that obtained by chemical mechanical polishing, which is the planarization method generally used for SiC substrates. To improve the removal rate, we investigated its dependence on rotational velocity and processing pressure. We found that the removal rate increases in proportion to both rotational velocity and processing pressure. A lapped 4H-SiC substrate was planarized under conditions that achieved the highest removal rate of approximately 500 nm/h. A smooth surface with a root-mean square roughness of less than 0.1 nm was fabricated within 15 min. Because the surface, which was processed under conditions of high rotational velocity and high processing pressure, consisted of a step–terrace structure, it was well ordered up to the topmost surface.

Complementary Characterization of Radioactivity Produced by Repetitive Laser-Driven Proton Beam Using Shot-to-Shot Proton Spectral Measurement and Direct Activation Measurement

2012-03-16T09:00:00+09:00

Authors: Koichi Ogura, Toshiyuki Shizuma, Takehito Hayakawa, Akifumi Yogo, Mamiko Nishiuchi, Satoshi Orimo, Akito Sagisaka, Alexander Pirozhkov, Michiaki Mori, Hiromitsu Kiriyama, Shuhei Kanazawa, Shuji Kondo, Yoshiki Nakai, Takuya Shimomura, Manabu Tanoue, Hajime Sasao, Daisuke Wakai, Fumitaka Sasao, Hajime Okada, Toyoaki Kimura, Yuji Oishi, Takuya Nayuki, Takashi Fujii, Koshichi Nemoto, and Hiroyuki Daido
The precision of the time-of-flight method for measuring proton spectra is confirmed by the activation method using a ^{7}Li(p,n)^{7}Be nuclear reaction. The proton beam driven by a repetitive high-intensity laser is utilized to induce the nuclear reaction. The activity measured by direct gamma-ray measurement after 1912 proton beam shots at 1 Hz is 1.7±0.2 Bq. This is in accordance with the activity of 1.6±0.2 Bq obtained from the shot-to-shot proton energy distribution measured using the time-of-flight detector.

Intelligent Ultraviolet Sensor Composed of GaN-Based Photodiode and N-Channel Metal Oxide Semiconductor Si-Charge Transfer Type Signal Processor

2012-03-15T09:00:00+09:00

Authors: ChangYong Lee, Fumiya Matsuno, Yoshinori Hashimoto, Hiroshi Okada, Kazuaki Sawada, and Akihiro Wakahara
Au/n-GaN Schottky barrier diode combined with Si-charge transfer type signal processor was investigated to realize intelligent UV sensors with low noise and high sensitivity. A 10-nm-thick Au was used for the semitransparent Schottky contact. The dark current–voltage characteristic of the Schottky barrier diode exhibited the ideal factor of 1.28 and barrier height of 1.1 eV. The sensitivity of 26.3 mA/W was obtained at a wavelength of 296 nm for 12 µW/mm^{2} UV irradiation power. Furthermore, the Au/n-GaN Schottky barrier diode was connected with the Si-charge transfer type signal processor to examine the effectiveness of the combined device for a UV detector. The processor was driven by a programmable function generator. Using the open-circuit voltage V_{oc} as the input signal, 350 mV output was achieved in a single integration cycle. The signal from the Schottky barrier diode was successfully amplified by accumulation operation of the Si-charge transfer type signal processor.

Dielectrophoretic Assembly of Semiconducting Carbon Nanotubes Separated and Enriched by Spin Column Chromatography and Its Application to Gas Sensing

2012-03-15T09:00:00+09:00

Authors: Michihiko Nakano, Masahiro Fujioka, Kaori Mai, Hideaki Watanabe, Yul Martin, and Junya Suehiro
The present authors have previously demonstrated the electrokinetic fabrication of a single-walled carbon nanotube (SWCNT) gas sensor by employing dielectrophoresis. Because this method employs mass-produced SWCNTs, it can realize cheaper and more flexible SWCNT gas sensor fabrication than that based on the on-site synthesis of SWCNTs. In this study, a new protocol was proposed and tested for the separation and enrichment of semiconducting SWCNTs, aiming to improve the SWCNT gas sensor sensitivity. The protocol employed a spin column filled with size-exclusion dextran-based gel beads as well as two surfactants (sodium dodecyl sulfate and sodium deoxycholate), which had different affinities to metallic and semiconducting SWCNTs. The separation and enrichment of the semiconducting SWCNTs were confirmed by measuring their optical and electrical properties. The CNT gas sensor fabricated using enriched semiconducting SWCNTs was highly sensitive to nitrogen dioxide (NO_{2}) gas, – more sensitive by 10 times than that fabricated using the pristine SWCNT mixture.

Formation of Graphene-Containing Porous Carbon Film for Electric Double-Layer Capacitor by Pulsed Plasma Chemical Vapor Deposition

2012-03-15T09:00:00+09:00

Authors: Masahiro Matsushima, Mikio Noda, Golap Kalita, Hideo Uchida, Koichi Wakita, and Masayoshi Umeno
Porous carbon films (PCFs) containing nanographene were deposited from a gas mixture of H_{2}, CH_{4}, and CO_{2} by pulsed discharge (PD) plasma-enhanced chemical vapor deposition (CVD) using a Ni catalytic layer, and their capacitance and conductance as an electrochemical double layer capacitor (EDLC) were investigated. The morphological study showed fiberlike structure formation with a 50-nm-thick Ni catalyst film. Nanographene-containing PCFs were deposited with a 100-nm-thick Ni film. When the Ni film thickness increased from 50 to 100 nm, the capacitance increased from 13 to 152 µF/cm^{2} and the conductance increased from 2.1 to 6.8 mS/cm^{2}. These results show that graphene-containing PCFs are very much suitable as electrode materials of EDLCs.

Optimization of the Dielectric Layer Thickness for Surface-Plasmon-Induced Light Absorption for Silicon Solar Cells

2012-03-14T09:00:00+09:00

Authors: Rui Xu, Xiaodong Wang, Wen Liu, Liang Song, Xiaona Xu, An Ji, Fuhua Yang, and Jinmin Li
In this study, we investigate the effect of dielectric layer thickness on light reflection due to random self-assembled Ag nanoparticles with diameters of less than 160 nm deposited on the Si substrate, indicating that a dielectric layer with an appropriate thickness is useful for reducing the amount of reflected light. In the short wavelength range, reflectivity is determined by the metallic plasmon and the SiO_{2} antireflection layer, and the effect of the surface plasmon dominates over the antireflection effect. In the long wavelength range, reflectivity decreases with increasing dielectric layer thickness and is determined by the oxide antireflection layer, while the effect of the surface plasmon is negligibly small. Moreover, the surface plasmon is affected by the SiO_{2} layer and Si substrate when the dielectric layer is thin; however, it is only determined by the SiO_{2} layer when the oxide layer is sufficiently thick. These observations have substantial applications for the optimization of surface-plasmon-enhanced silicon solar cells.

Implementation of Universal Broadband Visible Antireflection Coating for Various Glass Substrates Using Ion-Assisted Deposition

Yeuh-Yeong Liou, Li-Hsiang Kuo, Jhong-Yong Yan, and Cheng-Chung Jaing — 2012-03-14T09:00:00+09:00

Authors: Yeuh-Yeong Liou, Li-Hsiang Kuo, Jhong-Yong Yan, and Cheng-Chung Jaing
A normal-incidence universal broadband visible antireflection (AR) coating design, suited for commonly used glass substrates with refractive indices ranging from 1.472 to 1.750, was simulated using a spiral search approach, and then seven different substrates were coated simultaneously in one single deposition run to reduce their visible spectral reflectances by ion-assisted deposition. It was shown that the universal visible AR coating design of various substrates with refractive indices of 1.472, 1.517, 1.552, 1.619, 1.672, 1.718, and 1.750, obtained using the spiral search algorithm of a 2-material 10-layer system, was simplified to an 8-layer design, and the total average visible reflectance of practical AR-coated substrates was reduced from 5.55% for uncoated substrates to below 0.340%; the universal visible AR performance was found suitable. Moreover, this normal-incidence universal broadband visible AR coating also revealed an acceptable wide-angle visible antireflective effect for an incident angle range of 0–30°.

Fast Responsive Gas Sensor of Vertically Aligned Fluorine-Doped Tin Oxide Nanorod Thin Film

Chan-Woo Cho, Jong-Heun Lee, Doh-Hyung Riu, and Chang-Yeoul Kim — 2012-03-14T09:00:00+09:00

Authors: Chan-Woo Cho, Jong-Heun Lee, Doh-Hyung Riu, and Chang-Yeoul Kim
We prepared fluorine-doped tin oxide (FTO) nanorod films and a conventional FTO thin film for the application of a semiconducting gas sensor by spray pyrolysis method. The lengths of FTO nanorods (FTON, 100 and 500 nm) were controlled by changing deposition times, and FTO thin film (FTOT) was also prepared as a reference. The gas sensitivity test shows FTON with long nanorods had higher sensitivity for both hydrogen and ethanol gases but slow response and recovery times, despite an advantage of the higher gas sensitivity. FTO nanorod film with short length about 100 nm showed relatively lower sensitivity, but fast gas response and recovery characteristics. The fast response and recovery for the analyte gases are attributed to the conductance of FTO nanorods, which is closely related to the diameter and length of nanorods.

A Ferrofluidic Magnetic Micropump for Variable-Flow-Rate Applications

Chia-Yen Lee, Jik-Chang Leong, Yao-Nan Wang, Lung-Ming Fu, and Sih-Jia Chen — 2012-03-14T09:00:00+09:00

Authors: Chia-Yen Lee, Jik-Chang Leong, Yao-Nan Wang, Lung-Ming Fu, and Sih-Jia Chen
A novel micropump is proposed comprising two ferrofluidic plugs contained within a circular poly(methyl methacrylate) (PMMA) microchannel and a permanent magnet positioned beneath one of the plugs and driven by a rotating stepping motor. The ferrofluidic plugs are immiscible with the sample fluid. Thus, as the stepping motor rotates, the sample trapped between the two plugs is driven through the circular microchannel and exits the pump via the outlet diffuser. Meanwhile, more sample fluid is drawn into the microchannel on the inlet side. As a result, a continuous pumping effect is achieved. It is shown that the flow rate in the proposed device can be easily controlled by adjusting the rotational velocity of the stepping motor. In addition, for a constant motor velocity, the flow rate can be improved by increasing the circular channel width. The experimental results show that a maximum flow rate of 93 µl/min is obtained given a channel width of 1000 µm and a rotational velocity of 8 rpm. In addition, it is shown that the pump is capable of developing a maximum pressure head of 75 mm water (0.66 kPa) with channel width of 500 µm.

Effects of Ba Deficiency on Ion Ordering, Grain Growth, and Microwave Dielectric Properties of Ba_{1-x}Zn_{1/3}Nb_{2/3}O_{3} Ceramics

Jun Wang, Wenzhong Lu, and Wen Lei — 2012-03-13T09:00:00+09:00

Authors: Jun Wang, Wenzhong Lu, and Wen Lei
Ba_{1-x}Zn_{1/3}Nb_{2/3}O_{3} (0≤x≤0.02) ceramics were prepared by the solid-state reaction. The effects of Ba deficiency on the long-range order (LRO) of B-site ions, grain growth, and microwave dielectric properties of Ba_{1-x}Zn_{1/3}Nb_{2/3}O_{3} ceramics were investigated. Results show that Ba deficiency can effectively improve the sinterability of the ceramics and reduce the densification temperature by about 100 °C. The X-ray diffraction (XRD) and Raman spectra reveal that Ba-deficient samples exhibit a higher degree of LRO, and that the samples with x = 0.01 exhibit the highest degree of LRO. Furthermore, the degree of LRO increases with the decrease in sintering temperature in the range of 1400–1550 °C. Good microwave dielectric properties of ε_{r} = 39.8, Q ×f = 66532 GHz, and τ_{f} = +23.9 ppm/°C are obtained for the Ba-deficient samples with x = 0.01 when sintered at 1450 °C for 4 h. After a second sintering process at 1400 °C/10 h during cooling, the Q ×f values of Ba_{1-x}Zn_{1/3}Nb_{2/3}O_{3} ceramics are improved. An optimized Q ×f value of 72650 GHz is obtained for the Ba_{0.99}Zn_{1/3}Nb_{2/3}O_{3} (x = 0.01) ceramics after two-step sintering.

Comparison of Chemical Vapor Sensing Properties between Graphene and Carbon Nanotubes

2012-03-13T09:00:00+09:00

Authors: Hyung Goo Park, Sukju Hwang, Juhwan Lim, Duck-Hwan Kim, In Sang Song, Jae Hun Kim, Deok Ha Woo, Seok Lee, and Seong Chan Jun
We demonstrated the chemical-vapor sensing properties of graphene and carbon nanotubes (CNTs) by comparing their performances based on the two-dimensional exposure ratio. In order to implement the gas sensing, two kinds of sensors were properly prepared via the highly oriented pyrolytic graphite (HOPG) and CNT-dispersing methods, which cover different sensing area each other. Although the area of graphene is three times smaller than that of CNTs, the excellent sensing performance of graphene in the various concentration of the target gas is shown in terms of the sensitivity, the reactivity, and response time. We concluded this experimental result by focusing on the surface to volume ratio.

Effects of Substrate Temperature on Electrochromic Properties of Cobalt Oxide and Oxyhydroxide Thin Films Prepared by Reactive Sputtering Using O_{2} and H_{2}O Gases

KyoungMoo Lee, Yoshio Abe, Midori Kawamura, and Kyung Ho Kim — 2012-03-13T09:00:00+09:00

Authors: KyoungMoo Lee, Yoshio Abe, Midori Kawamura, and Kyung Ho Kim
Cobalt oxide and oxyhydroxide thin films were prepared by reactive sputtering of a Co target in O_{2} and H_{2}O gases at substrate temperatures from -20 to +200 °C. Co_{3}O_{4} films were formed at all the substrate temperatures in O_{2} gas and at 200 °C in H_{2}O gas, and amorphous CoOOH films were formed in the range from 10 to -20 °C in H_{2}O gas. A large transmittance change of approximately 26% and high electrochromic (EC) coloration efficiency of 20 cm^{2}/C at a wavelength of 600 nm were obtained for the CoOOH thin films deposited at -20 °C in 0.1 M KOH aqueous solution. The good EC performance of the CoOOH film is attributed to the low film density and amorphous structure.

Simultaneous In situ Measurement of Silicon Substrate Temperature and Silicon Dioxide Film Thickness during Plasma Etching of Silicon Dioxide Using Low-Coherence Interferometry

2012-03-13T09:00:00+09:00

Authors: Chishio Koshimizu, Takayuki Ohta, Tatsuo Matsudo, Shigeki Tsuchitani, and Masafumi Ito
We have successfully performed real-time noncontact monitoring of substrate temperature and thin film thickness during plasma etching using optical-fiber-based low-coherence interferometry. The simultaneous measurement of the silicon (Si) substrate temperature and the etching depth of the silicon dioxide (SiO_{2}) thin film on this substrate was performed in a dual-frequency capacitively coupled Ar/C_{4}F_{8}/O_{2} plasma. The SiO_{2} film thickness was deduced from the ratio of the interference intensity at the SiO_{2}/Si interface to that at the Si/air interface. The measurement error in the SiO_{2} film thickness was less than 11 nm. The temperature variation of the Si wafer was derived from the temperature change of its optical path length. The temperature measurement error, caused by the shift in optical path length due to the change in SiO_{2} film thickness, was reduced from 7.5 to 0.6 °C by compensating for the shift using the SiO_{2} thickness data. This method enables precise control of etching performance and improves process reproducibility.

Transient Current of Resistive Switching of a NiO_{x} Resistive Memory

Chih-Yi Liu, Jen-Yen Ho, Jyun-Jie Huang, and Hung-Yu Wang — 2012-03-12T09:00:00+09:00

Authors: Chih-Yi Liu, Jen-Yen Ho, Jyun-Jie Huang, and Hung-Yu Wang
A NiO_{x} thin film was fabricated by thermal oxidization on a Pt-coated substrate. Then, a Pt top electrode was deposited by an electron-beam evaporator to form a Pt/NiO_{x}/Pt structure. The NiO_{x}-based device can be reversibly switched between a high resistance-state (HRS) and a low resistance-state (LRS) by DC voltage sweeping. The resistive switching behavior occurs due to conducting filaments with a thermochemical reaction. A transient current was observed during the forming and SET processes (from a HRS to a LRS). The transient current increased with an increase in magnitude of the forming and SET voltage. The transient current was usually larger than the compliance current, and this caused the resistive switching behavior to be unstable. The transient current was caused by the discharge process of the parasitic capacitance of the measurement system. A circuit model of the measurement system was also proposed to simulate the transient current during the SET process. A resistor was series-wound with the NiO_{x}-based device to decrease the transient current during the forming and the SET processes. The series-wound resistor also increased the LRS resistance and reduced the RESET (from a LRS to a HRS) current.

Indium–Tin Oxide/Al Reflective Electrodes for Ultraviolet Light-Emitting Diodes

2012-03-12T09:00:00+09:00

Authors: Kosuke Takehara, Kenichiro Takeda, Shun Ito, Hiroki Aoshima, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, and Hiroshi Amano
We investigated indium–tin oxide (ITO)/Al reflective electrodes for improving the light extraction efficiency of UV light-emitting diodes (LEDs). The ITO layer showed high transparency in the UV region upon optimization of the thickness and annealing temperature. As a result, the ITO/Al electrode exhibited both high reflectivity in the UV region and good contact characteristics simultaneously. Using this electrode, we succeeded in improving the light output power of a 350 nm UV-A LED.

Reconstructions on AlN Nonpolar Surfaces in the Presence of Hydrogen

Toru Akiyama, Yasutaka Saito, Kohji Nakamura, and Tomonori Ito — 2012-03-12T09:00:00+09:00

Authors: Toru Akiyama, Yasutaka Saito, Kohji Nakamura, and Tomonori Ito
Structures and stability of nonpolar AlN(1-100) and (11-20) surfaces under hydrogen rich conditions are theoretically investigated by performing total-energy calculations within the density functional theory. The calculated surface energies demonstrate that several hydrogen incorporated structures are favorable depending on the chemical potentials of constituting elements. However, H atoms desorb and the relaxed ideal surfaces are stabilized even under the metal–organic vapor-phase expitaxy growth. These results suggest that the growth processes on AlN nonpolar surfaces are quite different from those of polar surfaces.

Low-Temperature, Solution-Processed Zinc Tin Oxide Thin-Film Transistors Fabricated by Thermal Annealing and Microwave Irradiation

Young Bum Yoo, Jee Ho Park, Se Jong Lee, Kie Moon Song, and Hong Koo Baik — 2012-03-07T09:00:00+09:00

Authors: Young Bum Yoo, Jee Ho Park, Se Jong Lee, Kie Moon Song, and Hong Koo Baik
In this study, we fabricated zinc tin oxide (ZTO) thin-film transistors (TFTs) using a sol–gel solution at a low annealing temperature of 350 °C. We found that the combination of conventional hot plate annealing and microwave irradiation was effective for achieving high performance of ZTO-TFTs. Solution-processed ZTO-TFTs prepared at 350 °C by microwave irradiation showed enhanced device characteristics of 1.84 cm^{2} V^{-1} s^{-1} mobility and a 10^{6} on/off current ratio. X-ray photoelectron spectroscopy analyses confirmed that residual hydroxyls in solution-processed ZTO films can be decomposed at low temperatures by microwave irradiation. Low-temperature microwave-assisted processing makes ZTO TFTs promising for use in flexible, transparent electronics.

Density Dependence of the Longitudinal Diffusion Coefficient of Electrons in Xenon

2012-03-07T09:00:00+09:00

Authors: Hiroki Kusano, José A. Matias-Lopes, Mitsuhiro Miyajima, Eido Shibamura, and Nobuyuki Hasebe
The longitudinal diffusion coefficient of electrons and the ratio of the longitudinal diffusion coefficient to the mobility of electrons were measured for the first time in high-density gaseous xenon in the extensive density range of 4.19×10^{19}–4.82×10^{20} cm^{-3}. The density dependence of the longitudinal diffusion coefficient was observed in the reduced electric field range of 0.025–0.055 Td.

Recent articles in Jpn. J. Appl. Phys.

Fabrication and Characterization of an FeBNdNb Magnetic Metallic Glass Thin Film

18-GHz, 4.0-aJ/bit Operation of Ultra-Low-Energy Rapid Single-Flux-Quantum Shift Registers

Comparison of Two Types of Recessed-Gate Normally-Off AlGaN/GaN Heterostructure Field Effect Transistors

Ultrasensitive Far-Infrared Phototransistors Fabricated in Superlattice Structures

Quantum Transport Theory of Direct Current Conductivity in the Presence of Spin–Orbit Interaction

Ratchet Effect of Single Vortex Motion in Superconducting Asymmetrical Nanobridges

Ultraviolet Photoresponse Properties of Single-Walled Carbon Nanotubes Decorated with Thickness-Controlled ZnO Layer by Pulsed Laser Deposition

Control of In Surface Segregation and Inter-Diffusion in GaAs on InGaP Grown by Metal–Organic Vapor Phase Epitaxy

Thermally Dried Ink-Jet Process for 6,13-Bis(triisopropylsilylethynyl)-Pentacene for High Mobility and High Uniformity on a Large Area Substrate

Hybrid Method for Analyzing the Torsional Vibration of One-Dimensional Phononic-Band-Gap Shafts

Transparent Conductive Distributed Bragg Reflectors Composed of High and Low Refractive Index Transparent Conductive Films

Buffer-Related Degradation Aspects of Single and Double-Heterostructure Quantum Well InAlN/GaN High-Electron-Mobility Transistors

Simulation of Material Properties of Barium Titanate Single Crystal with Multidomain Structure Using Modified Time-Dependent Devonshire–Ginzburg–Landau Model

Thermo-Optical Tuning of Whispering Gallery Modes in Erbium:Ytterbium Doped Glass Microspheres to Arbitrary Probe Wavelengths

Ge Flat Layer Growth on Heavily Phosphorus-Doped Si(001) by Sputter Epitaxy

Thresholds of Etchable Track Formation and Chemical Damage Parameters in Poly(ethylene terephthalate), Bisphenol A polycarbonate, and Poly(allyl diglycol carbonate) Films at the Stopping Powers Ranging from 10 to 12,000 keV/µm

Practical Guidance of Parameter Extraction for Device Simulation of Thin-Film Transistors

Adsorption of Pyrazine on a Si(001) Surface Partially Covered with an Indium Dimer Structure

Development of Low-Temperature Sintering Technique for Dye-Sensitized Solar Cells Combined with Dielectric Barrier Discharge Treatment

Magnetic Alignment of Magnetically Biaxial Diamagnetic Rods under Rotating Magnetic Fields

A Comparative Study on the Optical and Electrical Properties of Si-Doped Polar and Nonpolar GaN

Theoretical Evaluation of Ballistic Electron Transport in Field-Effect Transistors with Semiconducting Graphene Channels

Translation from Schottky Barrier to Atomic Bridging-Type Surface Photovoltages in Cr-Aqueous-Solution-Rinsed Si(001) Wafers

Discriminated Detection of Nuclear Tracks Recorded on Multilayers of Photographic Emulsions with Different Sensitivities by Color-Development Method

Synthesis and Magnetic Properties of NiSe, NiTe, CoSe, and CoTe

A New Two-Dimensional Analytical Threshold Voltage Model for Short-Channel Triple-Material Surrounding-Gate Metal–Oxide–Semiconductor Field-Effect Transistors

Photocatalytic Activity of WO_{3} Films Crystallized by Postannealing in Air

Primary Factor Extracted for Anomalous Decline of Drain Current in Metal–Oxide–Semiconductor Field-Effect Transistors

Uniform Dispersion of Liquid Crystal Droplets in the Polymer Matrix by Chemical Affinity Difference-Induced Phase Separation

Application of a Continued-Fraction-Based Theory to Line-Profile in Mn-Doped GaN Film

Near-Edge X-Ray Absorption Fine Structure Study of Vertically Aligned Carbon Nanotubes Grown by the Surface Decomposition of SiC

The Diagnosis Method for High-Energy Ion Beams Using Backscattered Particles for Laser-Driven Ion Acceleration Experiments

Optical Characterization of Double Peak Behavior in 10-11 Semipolar Light-Emitting Diodes on Miscut m-Plane Sapphire Substrates

Monomode Optical Waveguides in Yb^{3+}-Doped Silicate Glasses Produced by Low-Dose Carbon Ion Implantation

Optical and Transport Anisotropy in Poly(9,9'-dioctyl-fluorene-alt-bithiophene) Films Prepared by Floating Film Transfer Method

Ultra-Conformal Metal Coating on High-Aspect-Ratio Three-Dimensional Structures Using Supercritical Fluid: Controlled Selectivity/Non-Selectivity

10 Gbps Colorless Optical Source in Wavelength-Division Multiplexed Passive Optical Networks for Monolithic Integration of Deep-Ridge Waveguide Electroabsorption Modulator with Planar Buried-Heterostructure Semiconductor Optical Amplifier

Crack-Free AlN/GaN Distributed Bragg Reflectors on AlN Templates

Efficient Ultraviolet Rotational Raman Lidar for Temperature Profiling of the Planetary Boundary Layer

Simulation Study on Insulated Gate Bipolar Transistor Turn-Off Oscillations

Influence of Interfacial Tantalum Oxynitride on Resistive Switching of Cu/Cu–SiO_{2}/TaN

Computational Nano-Materials Design of Low Cost and High Efficiency Cu_{2}ZnSn[Se_{1-x}S_{x}]_{4} Photovoltaic Solar Cells by Self-Organized Two-Dimensional Spinodal Nanodecomposition

Fabrication and Characterization of Bragg Reflector Slow-Light Waveguide with Oxide Lateral Confinement

Shape Control of Trenched 4H-SiC C-Face by Thermal Chlorine Etching

Topographic Contrast in Force Modulation Atomic Force Microscopy Images

Effect of Frequency on the Change in Backscattered Ultrasound Energy as a Function of Temperature

Rotation-Symmetric Multispot Focusing Phase-Shifted Grating Coupler for Integrated Semiconductor Laser

Quantitative Analysis of Surface Morphology of Boron-Doped Zinc Oxide for Microcrystalline Silicon Solar Cells

Three-Dimensional Reciprocal-Lattice Analysis Using Azimuth-Scan Reflection High-Energy Electron Diffraction: Determination of Complex Crystal Orientations of Al Grains on Si(111) Surface

Self-Organized Nanostructures and High Blocking Temperatures in MgO-Based d^{0} Ferromagnets

Synthesis of Nitrogen-Doped Graphene by Plasma-Enhanced Chemical Vapor Deposition

Effects of Plasma Processes on the Characteristics of Optical Device Structures Based on GaAs

Carbon Nanotube Research: Past and Future

Study of Active Micromixer Driven by Electrothermal Force

Characterization of Photoexcited Carriers and Thermal Properties of Nanoparticulate TiO_{2} Film Using Heterodyne Transient Grating Method

Effect of Nucleation Layer of Photocatalytic TiO_{2} Thin Film Prepared by Two-Step Deposition Using Radical-Assisted Sputtering

Properties of Inductively Coupled Radio Frequency CH_{4}/H_{2} Plasmas: Experiments and Global Model

Ultrathin Reflective Flexible Liquid Crystal Display Film

Relationship between Concentration of Initiator and Image-Sticking Phenomenon of Polymer-Sustained-Alignment Liquid Crystal Displays

Effects of Electrospun TiO_{2} Nanowires Mixed in Nanoparticle-Based Electrode for Dye-Sensitized Solar Cells

A New Collinear-Type Energy-Filtered X-ray Photoemission Electron Microscope Equipped with a Multi-Pole Aberration-Corrected Air-Core Coil Wien Filter

Low-Voltage Mach–Zehnder Modulator with InGaAs/InAlAs Five-Layer Asymmetric Coupled Quantum Well

Theoretical Analysis on Mechanical Deformation of Membrane-Based Photomask Blanks

Mn_{2}O_{3} Slurry Achieving Reduction of Slurry Waste

Comprehensive Study of the X-Ray Photoelectron Spectroscopy Peak Shift of La-Incorporated Hf Oxide for Gate Dielectrics

Microscopic Structure of Stepwise Threading Dislocation in 4H-SiC Substrate

Unidirectional Liquid Crystal Pretilt Generation on Asymmetric Nanoscaled Groove Pattern Driven by Atomic Force Microscopic Tip

Investigation of Optical and Electrochromic Properties of Tungsten Oxide Deposited with Horizontal DC and DC Pulse Magnetron Sputtering

Electrostatic Properties of Organic Monolayers on Silicon Oxides Studied by Kelvin Probe Force Microscopy

Evaluation and Control of Break-Even Time of Nonvolatile Static Random Access Memory Based on Spin-Transistor Architecture with Spin-Transfer-Torque Magnetic Tunnel Junctions

Dielectric Properties of Y_{2}O_{3} and Nb_{2}O_{5} Co-Doped Barium Titanate Ceramics

AC Power Consumption of Single-Walled Carbon Nanotube Interconnects: Non-Equilibrium Green's Function Simulation

Characterization of Interfaces between HfO_{2} Thin Film and Metal Electrode with Pre–Post Treatments

Fabrication and Electrical Properties of Thermally Oxidized p-Channel Metal–Oxide–Semiconductor Field-Effect Transistors on 4H-SiC C-Face

Organic Field-Effect-Transistor-Based Memory with Nylon 11 as Gate Dielectric

A Compact 2 Degree-of-Freedom Energy Harvester with Cut-Out Cantilever Beam

Analyzing Photo Induced Internal Electric Field in Pentacene/C_{60} Double-Layer Organic Solar Cells under Various External Voltages by Electric-Field-Induced Optical Second Harmonic Generation Measurement

Effect of Seed Layer on Room Temperature Tunnel Magnetoresistance of MgO Barriers Formed by Radical Oxidation in IrMn-Based Magnetic Tunnel Junctions

Analysis of the Influence of Sputtering Damage to Polymer Gate Insulators in Amorphous InGaZnO_{4} Thin-Film Transistors