Particle Size Determining Equation in Metallic Nanopowder Preparation by Pulsed Wire Discharge

2013-04-22T09:00:00+09:00

Authors: Yoshinori Tokoi, Hong-Baek Cho, Tsuneo Suzuki, Tadachika Nakayama, Hisayuki Suematsu, and Koichi Niihara
Copper nanopowders are prepared by pulsed wire discharge (PWD) using copper wires in nitrogen gas. From experimental results obtained in the present study and published literature, a relationship to predict the particle size of powders prepared by PWD is proposed. A theoretical plasma/vapor density (D_{th}), which is the most important factor for controlling the particle size is defined as mPE_{c}^{-1}, where m, P, and E_{c} are the weight of the wire, pressure of nitrogen gas, and charged energy in the capacitor, respectively. From high-speed photographs obtained during PWD, the relationship between the measured D_{exp} and D_{th} is shown by D_{exp}∝D_{th}^{0.6}. The relationship between the median particle diameter d_{50} and D_{th} is found to be d_{50}∝D_{exp}∝(D_{th}^{0.6})^{0.4} by transmission electron microscopy observations. This empirical relationship is in agreement with that expected from the formation and growth of particles via Brownian coagulation of free molecules. From the above relationship, it is possible to predict and control the particle size of powders prepared by PWD.

GaAs/InGaP Core–Multishell Nanowire-Array-Based Solar Cells

Eiji Nakai, Masatoshi Yoshimura, Katsuhiro Tomioka, and Takashi Fukui — 2013-04-22T09:00:00+09:00

Authors: Eiji Nakai, Masatoshi Yoshimura, Katsuhiro Tomioka, and Takashi Fukui
Semiconductor nanowires (NWs) are good candidate for light-absorbing material in next generation photovoltaic and III–V NW-based multi-heterojunction solar cells using lattice-mismatched material system are expected as high energy-conversion efficiencies under concentrated light. Here we demonstrate core–shell GaAs NW arrays by using catalyst-free selective-area metal organic vapor phase epitaxy (SA-MOVPE) as a basis for multijunction solar cells. The reflectance of the NW array without any anti-reflection coating showed much lower reflection than that of a planar wafer. Next we then fabricated core–shell GaAs NW array solar cells with radial p–n junction. Despite the low reflectance, the energy-conversion efficiency was 0.71% since a high surface recombination rate of photo-generated carriers and poor ohmic contact between the GaAs and transparent indium–tin-oxide (ITO) electrode. To avoid these degradations, we introduced an InGaP layer and a Ti/ITO electrode. As a result, we obtained a short-circuit current of 12.7 mA cm^{-2}, an open-circuit voltage of 0.5 V, and a fill factor of 0.65 for an overall efficiency of 4.01%.

Deposition of Ag(In,Ga)Se_{2} Solar Cells by a Modified Three-Stage Method Using a Low-Temperature-Deposited Ag–Se Cap Layer

2013-04-22T09:00:00+09:00

Authors: Zhang Xianfeng, Tsuyoshi Kobayashi, Yasuyoshi Kurokawa, Shinsuke Miyajima, and Akira Yamada
Ag(In,Ga)Se_{2} (AIGS) films with a uniform Ag depth profile were successfully deposited by a modified three-stage method in which a Ag–Se layer was pre deposited at a low temperature (350 °C) before a high-temperature process at around 600 °C. The Ag–Se layer acted as a cap layer and effectively prevented the desorption of In from the films during the high-temperature process. The In/(In+Ga) ratio of the AIGS films was found to be about 0.15. The best AIGS solar cell deposited by this method showed an active area conversion efficiency of 10.7%.

Characteristics of Electron Conduction in a Gas under a Quadrupole Magnetic Field and Radio-Frequency Electric Fields

Hirotake Sugawara — 2013-04-22T09:00:00+09:00

Authors: Hirotake Sugawara
Electron conduction in CF_{4} under a simplified model quadrupole magnetic field (QMF) and rf electric fields at f = 13.56, 27.12, and 40.68 MHz was analyzed using a Monte Carlo method, following the manner of electron swarm analyses. This field configuration simulated current paths of magnetic neutral loop discharge plasmas used for dry etching. The electron conduction therein was focused on as an elemental process of plasma power deposition. The electrons formed a star-shaped distribution with four rays along the separatrices of the QMF. The effective electron conductivity quantified as the amplitude of mean electron velocity was high around the central axis. The time-averaged mean electron velocities in the four regions of the QMF were biased under a rectification effect of the magnetic field. With increasing f, the high-conductivity region expanded and ionization was promoted. An enhancement of plasma power deposition under high driving frequencies was indicated.

Effect of Indium–Tin-Oxide Schottky Contact on the Resistance Switching of NiO Film

2013-04-19T09:00:00+09:00

Authors: Young Soo No, Dong-Hee Park, Jeon-Kook Lee, Youn-Seoung Lee, Tae Whan Kim, and Won-Kook Choi
The effect of electrode materials on resistance switching was evaluated on the Pt/NiO/electrode (EL) structures where the EL contacts were Pt, Al, and indium–tin-oxide (ITO). It was confirmed that ohmic Pt contact needs to induce the effective electric field for resistance switching across the NiO film. For the Pt/NiO/Al structure, the barrier height of the Al Schottky contact was measured as 0.66 eV and no resistance switching was observed owing to a large voltage drop at the rectifying interface induced by the reduction of NiO resulting from the formation of Al oxide. In the ITO (EL)/NiO/Pt structure, the barrier height of the Schottky contact between ITO and NiO was about 0.52 eV and it did not show any resistance switching, either. Through the depth-profile study by X-ray photoelectron spectroscopy, chemical reactions at the interface ITO/NiO was identified to be not too much evolved compared with that of NiO/Al, which might due to be abundant oxygen on the ITO surface. Such Schottky barrier heights 0.52–0.66 eV were considered too high to induce a sufficient electric field in the NiO film causing the resistance switching.

Electro-optical Characteristics of Ferroelectric Liquid Crystal Embedded in Photonic Crystal Fiber

Jeong-Seon Yu, Jong Sung Yu, and Jong-Hyun Kim — 2013-04-19T09:00:00+09:00

Authors: Jeong-Seon Yu, Jong Sung Yu, and Jong-Hyun Kim
The confinement of liquid crystals in a small space induces interesting phenomena that deviate from the bulk properties. We report on the electro-optical properties of ferroelectric liquid crystals (FLCs) confined in transparent photonic crystal fibers (PCFs). A PCF has a large number of cylindrical air holes of micrometer size and they are filled with FLCs. Optical measurements indicate that the directors are parallel to the axis of PCF and the layers are inclined relative to the cylindrical wall with the tilt angle of SmC^{*}. The electro-optical response depends on the surface condition and shows the unusual double hysteresis loop. We discuss the possible configuration of director arrangement and the electro-optical properties of FLC on the basis of a simple model.

Formation of Titanium Nitride on the GaN(0001) Surface: A Density Functional Theory Study

2013-04-19T09:00:00+09:00

Authors: César Ortega-Lopez, William López-Perez, and Rafael González-Hernández
We have carried out density functional theory (DFT) calculations to study the role of titanium impurity atoms during gallium nitride (GaN) growth. Adsorption and incorporation of Ti atoms on GaN(0001) surface is examined and it is shown that Ti atoms preferentially adsorb at the T_{4} sites at low and high coverage. In addition, calculating the formation energy of multiple-impurity configurations, we constructed a surface phase diagram showing the energetically most stable structures as a function of Ti and Ga chemical potentials. Based on these, we find that incorporation of Ti atoms in the Ga-substitutional site is energetically more favorable compared with the Ti surface adsorption on the top layers. This effect leads to the formation of an interfacial crystalline titanium nitride (TiN) compound on the GaN(0001) surface, which can offer a good interfacial combination between Ti and GaN substrates.

Broad and Flat Brillouin Gain Spectrum in Optical Fiber Obtained by Modulating Driving Current of Laser Diode

Yosuke Mizuno, Neisei Hayashi, and Kentaro Nakamura — 2013-04-19T09:00:00+09:00

Authors: Yosuke Mizuno, Neisei Hayashi, and Kentaro Nakamura
A simple method for obtaining a broad and flat Brillouin gain spectrum (BGS) is presented. By modulating the driving current of a pump laser diode with triangular waveform, a BGS with lower than 0.3 dB gain variation over >200 MHz is achieved. With this method, the bandwidth of the flattened BGS can be controlled by adjusting the amplitude and/or frequency of the current modulation.

Formation of Semi-Insulating Layers on Semiconducting β-Ga_{2}O_{3} Single Crystals by Thermal Oxidation

2013-04-18T09:00:00+09:00

Authors: Takayoshi Oshima, Kenichi Kaminaga, Akira Mukai, Kohei Sasaki, Takekazu Masui, Akito Kuramata, Shigenobu Yamakoshi, Shizuo Fujita, and Akira Ohtomo
Semi-insulating layers (SIL) were formed on the surfaces of nominally undoped β-Ga_{2}O_{3} (010) single crystals by thermal oxidation. Capacitance–voltage measurement with double Schottky configuration was performed to evaluate the increase in the thickness of the SIL as a function of annealing temperature and time. A SiO_{2} layer prepared on the surface prevented the extension of the SIL, indicating that oxygen incorporation from air and successive bulk diffusion dominated the carrier compensation process. The activation energy of oxygen diffusion coefficient was estimated to be 4.1 eV.

Center Wavelength Adoption Techniques for Supercontinuum Generating Highly Nonlinear Noncircular Core Photonic Crystal Fiber

Md. Anwar Hossain and Yoshinori Namihira — 2013-04-18T09:00:00+09:00

Authors: Md. Anwar Hossain and Yoshinori Namihira
A supercontinuum (SC) light source is designed using a highly nonlinear noncircular core photonic crystal fiber (HNL-NcPCF) with all-normal group velocity dispersion (GVD) to demonstrate how simply an SC can be generated at different center wavelengths in a normal GVD regime. Using the finite element method (FEM) with a perfectly matched layer (PML), the design of two or more PCF-based light sources at different neighboring center wavelengths is demonstrated numerically. Moreover, SC generations are demonstrated numerically at 1.06, 1.31, and 1.55 µm in a normal dispersion regime using picosecond optical pulses.

1 ms Pulse Beam Generation and Acceleration by Photocathode Radio Frequency Gun and Superconducting Accelerator

2013-04-18T09:00:00+09:00

Authors: Masao Kuriki, Hokuto Iijima, Seiichi Hosoda, Ken Watanabe, Hitoshi Hayano, Junji Urakawa, Goro Isoyama, Ryukou Kato, Keigo Kawase, Ayaka Kuramoto, Shigeru Kashiwagi, and Kazuyuki Sakaue
We report the successful generation and acceleration of a 1-ms-long pulse and multibunch electron beam by a normal conducting photocathode RF gun and a super conducting accelerator at the KEK Superconducting Test Facility (STF). A 1.3 GHz normal conducting RF gun generates a 1 ms and 10 mA macropulse that fully satisfies the designed parameters. This is the longest macropulse generated by a normal conducting RF gun with a frequency of more than 1 GHz. A beam acceleration of up to 40 MeV was demonstrated with more than 60% of the designed average current. The accelerated beam properties were evaluated: the intensity and energy fluctuations were 3.8% and less than 0.08%, respectively. These beam properties are sufficient for the requirement of the STF operation including that in the quantum beam project, which is high-brightness-X-ray generation by inverse laser Compton scattering. The intensity fluctuation should be improved toward the International Linear Collider (ILC) for uniform acceleration.

Performance Estimation of Silicon-Based Self-Cooling Device

Shinji Fukuda, Yuichi Sabi, Toshio Kawahara, and Satarou Yamaguchi — 2013-04-16T09:00:00+09:00

Authors: Shinji Fukuda, Yuichi Sabi, Toshio Kawahara, and Satarou Yamaguchi
Since self-cooling devices were first proposed, several materials have been tested for their suitability to be used in them. A self-cooling device requires a high Seebeck coefficient, a low electrical resistivity, and a high thermal conductivity. Here, we report experimental results for single-crystal silicon doped with boron. Samples were fabricated with carrier densities in the range of 2.0×10^{15} to 1.6×10^{19} cm^{-3}, and their Seebeck coefficient and electrical resistivity were measured. Silicon with a carrier density of 1.6×10^{19} cm^{-3} has a power factor of 4.8×10^{-3} W/(K^{2}·m) at room temperature. The cooling capability of a self-cooling device was estimated using a one-dimensional model. The results suggest that a self-cooling device based on silicon with a high carrier density can have a higher heat removal performance than a conventional silicon power device of the same size.

Development of A Semiconductor Laser Based High Temperature Fine Thermal Energy Source in an Optical Fiber Tip for Clinical Applications

Takahiro Fujimoto, Yusuke Imai, Kazuyoku Tei, and Shigeru Yamaguchi — 2013-04-15T09:00:00+09:00

Authors: Takahiro Fujimoto, Yusuke Imai, Kazuyoku Tei, and Shigeru Yamaguchi
A new technique for generating high temperatures on the surface of an optical fiber is developed for medical applications using lower-power semiconductor lasers with output powers lower than 10 W. Using a power level of 4–6 W semiconductor laser with a pulse duration of 180 ms at a wavelength of 980 nm, a laser-coupled fiber tip was once processed to contain a certain amount of Ti with a depth of 100 µm from the tip surface so that the laser energy could be efficiently absorbed to be transferred to thermal energy. With consecutive laser pulse irradiation, the tip processed fiber (TP fiber) served as a reproducible fine heat source whose temperature was measured to be in excess 3100 K based on two-color thermometry. Processing of ceramic and niobium plate, which are hardly ablated with direct low power (6 W) irradiation, was successfully demonstrated by contacting the TP fiber excited with the same power.

Influence of Isoelectronic Te Doping on the Physical Properties of ZnO Films Grown by Molecular-Beam Epitaxy

2013-04-15T09:00:00+09:00

Authors: Seung-Hwan Park, Tsutomu Minegishi, Dong-Cheol Oh, Dong-Jin Kim, Ji-Ho Chang, Takafumi Yao, Toshinori Taishi, and Ichiro Yonenaga
In molecular-beam epitaxy, isoelectronic Te doping induces the serious change of the physical properties of ZnO films: i) Incorporated Te concentration is proportional to the 2.2th power of injected Te flux in the logarithmic scale; ii) Te-doped ZnO lattices are dominated by the relaxation mechanism of compressive strain; iii) incorporated Te atoms substitute to the O sites of ZnO lattices; iv) the low-level injection of Te atoms below ∼10^{19} cm^{-3} improves the crystalline quality in the ZnO films; and v) isoelectronic Te centers act as donor impurities, resulting in the increase of electrons in the ZnO films.

Inactivation Process of Penicillium digitatum Spores Treated with Non-equilibrium Atmospheric Pressure Plasma

2013-04-15T09:00:00+09:00

Authors: Hiroshi Hashizume, Takayuki Ohta, Takumi Mori, Sachiko Iseki, Masaru Hori, and Masafumi Ito
To investigate the inactivation process of Penicillium digitatum spores treated with a non-equilibrium atmospheric pressure plasma, the spores were observed using a fluorescent microscope and compared with those treated with ultraviolet (UV) light or moist heat. The treated spores were stained with two fluorescent dyes, 1,1'-dioctadecyl-3,3,Y,3'-tetramethylindocarbocyanine perchlorate (DiI) and diphenyl-1-pyrenylphosphine (DPPP). The intracellular organelles as well as cell membranes in the spores treated with the plasma were stained with DiI without a major morphological change of the membranes, while the organelles were never stained in the spores treated with UV light or moist heat. Moreover, DPPP staining revealed that organelles were oxidized by plasma treatment unlike UV light or moist heat treatments. These results suggest that only plasma treatment induces a minor structural change or functional inhibition of cell membranes, which leads to the oxidation of the intracellular organelles without a major deformation of the membranes through the penetration of reactive oxygen species generated by the plasma into the cell.

Scanning Probe Lithography with Negative and Positive Electron Beam Resists

Lydia Anggraini, Bungo Tanaka, Naoki Matsuzuka, and Yoshitada Isono — 2013-04-15T09:00:00+09:00

Authors: Lydia Anggraini, Bungo Tanaka, Naoki Matsuzuka, and Yoshitada Isono
In this research, we focus on scanning probe lithography (SPL) to create nanostructures of negative and positive electron beam (EB) resists on a silicon (Si) substrate by common scanning probe microscopy (SPM). Microposit SAL 601 and ZEP 520A are used as the negative and positive EB resists, respectively. The EB resist films of 40–50 nm thickness are used for writing nanopatterns with low-energy electrons emitted from the probe tip in SPM. The effect of the baking conditions on nanopatterning for each resist film is experimentally investigated, and suitable baking conditions for both EB resist films are determined. The nanostructures of both resists baked under each set of suitable conditions are created under several writing conditions in order to confirm the possibility of nanopatterning and the controllability of the line width of the nanostructures. In addition, we discuss the prediction method for the line width on the basis of analysis of the static electric field inside the resist films.

Comparison between Grazing and Off-Grazing Resonance Emissions of Stimulated Superradiance in an Undulator Channel

Yoon Ho Seo — 2013-04-12T09:00:00+09:00

Authors: Yoon Ho Seo
The effect of bunch slippage in stimulated superradiance emitted from short electron bunches in an undulator channel at the off-grazing resonance is discussed. Comparison between off-grazing and grazing resonance emissions shows that the emitted power in the early radiation-build-up stage significantly decreases owing to the bandwidth restriction caused by slippage. The influence of bunch-pulse detachment due to the slippage seems to be minimized by the proper positioning of the excited pulse.

Production of Single-Walled Carbon Nanotubes by Modified Arc Discharge Method

Mohammad Jellur Rahman and Tetsu Mieno — 2013-04-12T09:00:00+09:00

Authors: Mohammad Jellur Rahman and Tetsu Mieno
Single-walled carbon nanotubes (SWNTs) are synthesized by the arc discharge method in He gas, where three directions of discharge current relative to gravity are selected and their production rates are compared. The soot production rate for the upward discharge current is larger than those for the horizontal and downward discharge currents. Also, the qualities of the produced SWNTs for the three cases are almost the same. The effect of a steady magnetic field (3.0 mT) perpendicular to the discharge current direction (J×B arc discharge) is also examined. This magnetic field increases the soot production rate for all three discharge current directions. The estimated ratio of the number of SWNT bundles to the number of carbon particles is higher for the upward discharge current in the case of B = 0. This ratio increases significantly for the horizontal and downward discharge currents when a magnetic field is applied.

Determination of Liquid Density and Viscosity Using a Self-Actuating Microcantilever

Don Hur and Jeong Hoon Lee — 2013-04-12T09:00:00+09:00

Authors: Don Hur and Jeong Hoon Lee
A sensor for determining liquid density and viscosity using a self-actuating microcantilever is proposed. A microcantilever incorporating piezoelectric thin films with seven multilayers was fabricated in order to acquire a direct electrical signal. As proof of the operating principle and sensitivity, the change in resonant frequency peak (f_{res}) and full width at half maximum (FWHM; Δf) values with liquid viscosity and density were we measured using the glycerol-water solutions with various glycerol concentrations. With increasing liquid viscosity from 1 to 600 cP, an increase in FWHM from 2920 to 10314 Hz was observed. Also, it was observed that shifts in the resonant frequency decreased with increasing liquid density. Using nonlinear regression fitting between liquid density and f_{res}^{2}, the presented self-sensing microcantilever could potentially provide a solid platform for real-time monitoring of liquid density.

Small-Signal Analysis of the Voltage-Dependent Nonlinearity in High-Power Uni-Traveling-Carrier Photodiodes

Dong-Soo Shin — 2013-04-12T09:00:00+09:00

Authors: Dong-Soo Shin
It is demonstrated with small-signal analysis how the voltage-dependent responsivity in the uni-travelling-carrier photodiode (UTC PD) can lead to the intermodulation distortion. A simple expression for the third-order output intercept point (OIP3) is derived and compared with experiments. Reasonable agreements between the theoretical and experimental OIP3 values are observed.

A Multimode Relayed Piezoelectric Cantilever for Effective Vibration Energy Harvesting

Chuan Li, Daewoong Hong, Kwang-Ho Kwon, and Jaehwa Jeong — 2013-04-11T09:00:00+09:00

Authors: Chuan Li, Daewoong Hong, Kwang-Ho Kwon, and Jaehwa Jeong
A piezoelectric cantilever with an eccentrically connected wire-mass relay is proposed for extensive energy harvesting from broadband vibration responses. The relay mass is chosen to be much greater than that of the cantilever. The vibration source is magnified by the relay as a bending-swinging-torsional excitation to drive the cantilever. Thus, multiple vibration modes of the cantilever are effectively employed to enhance energy harvesting. A prototype device was developed and characterized. The results show that the proposed structure can generate much more electricity over a broader bandwidth than conventional structures.

Electro-Optic Coefficient r_{51} of LiNbO_{3} Crystal Obtained from Measurement of Retardation Induced by Square of Electric Field

Kuniharu Takizawa, Koshi Haraguchi, Lianhua Jin, and Seiichi Suzuki — 2013-04-11T09:00:00+09:00

Authors: Kuniharu Takizawa, Koshi Haraguchi, Lianhua Jin, and Seiichi Suzuki
A versatile method of measuring electro-optic coefficients (r_{ij}: i=4–6 and j=1–3) of isometric, uniaxial, and biaxial crystals without crystal coordinate rotation has been developed. It has been confirmed theoretically and experimentally that the change in the retardation of an X-cut Y-propagation LiNbO_{3} crystal depends on the square of the electric field along the X-direction. The constant stress electro-optic coefficient r_{51} of the LiNbO_{3} crystal is found to be 32.05±0.01 pm/V at 632.8 nm.

Atomic-Resolution X-ray Energy-Dispersive Spectroscopy Chemical Mapping of Substitutional Dy Atoms in a High-Coercivity Neodymium Magnet

2013-04-09T09:00:00+09:00

Authors: Masaru Itakura, Natsuki Watanabe, Minoru Nishida, Takeshi Daio, and Syo Matsumura
We have investigated local element distributions in a Dy-doped Nd_{2}Fe_{14}B hot-deformed magnet by atomic-column resolution chemical mapping using an X-ray energy-dispersive spectrometer (XEDS) attached to an aberration-corrected scanning transmission electron microscope (Cs-corrected STEM). The positions of the Nd and Dy atomic columns were visualized in the XEDS maps. The substitution of Dy was limited to a surface layer 2–3 unit cells thick in the Nd_{2}Fe_{14}B grains, and the Dy atoms preferentially occupied the 4f-Nd sites of Nd_{2}Fe_{14}B. These results provide further insights into the principal mechanism governing the coercivity enhancement due to Dy doping.

Review of Emerging New Solid-State Non-Volatile Memories

Yoshihisa Fujisaki — 2013-04-08T09:00:00+09:00

Authors: Yoshihisa Fujisaki
The integration limit of flash memories is approaching, and many new types of memory to replace conventional flash memories have been proposed. Unlike flash memories, new nonvolatile memories do not require storage of electric charges. The possibility of phase-change random-access memories (PCRAMs) or resistive-change RAMs (ReRAMs) replacing ultrahigh-density NAND flash memories has been investigated; however, many issues remain to be overcome, making the replacement difficult. Nonetheless, ferroelectric RAMs (FeRAMs) and magnetoresistive RAMs (MRAMs) are gradually penetrating into fields where the shortcomings of flash memories, such as high operating voltage, slow rewriting speed, and limited number of rewrites, make their use inconvenient. For instance, FeRAMs are widely used in ICs that require low power consumption such as smart cards and wireless tags. MRAMs are used in many kinds of controllers in industrial equipment that require high speed and unlimited rewrite operations. For successful application of new non-volatile semiconductor memories, such memories must be practically utilized in new fields in which flash memories are not applicable, and their technologies must be further developed.

Energetics of Quantum Dot Formation and Relaxation of InGaAs on GaAs(001)

Markus Pristovsek, Raimund Kremzow, and Michael Kneissl — 2013-04-05T09:00:00+09:00

Authors: Markus Pristovsek, Raimund Kremzow, and Michael Kneissl
We studied InGaAs quantum dots (QD) formation, the evolutions of QD density, and relaxation as function of indium content and layer thickness on GaAs(001). The results as well as literature show that deposition of InAs after QD formation increases linearly the QD density. This indicates a single constant energy is released per QD. The strain energy at the onset of QD formation and relaxation is constant, i.e., independent of the indium content. Thus relaxation and QD formation can be described better by using a constant critical strain energy of 4.0 eV/nm^{2} compared to theories based on balancing the energy/force of dislocations with the strain. QD were only found above 40–50% of indium, while for lower indium contents a dislocation network forms. The reason is a surface transition from c(4×4) to (2×4)-like which promotes nucleation and hence QD formation.

Polarization Switching Dynamics of Vinylidene Fluoride/Trifluoroethylene Copolymer Thin Films under High Electric Field at Various Temperatures

Hajime Ishii, Takashi Nakajima, Takeo Furukawa, and Soichiro Okamura — 2013-04-03T09:00:00+09:00

Authors: Hajime Ishii, Takashi Nakajima, Takeo Furukawa, and Soichiro Okamura
The polarization switching times of vinylidene fluoride (VDF)/trifluoroethylene (TrFE) copolymer thin films with a thickness of 40 nm were measured at temperatures ranging from -50 to 50 °C and applied fields ranging from 75 to 600 MV/m. The switching time was drastically reduced by increasing the applied field at all temperatures. The relationship between the switching time and the reciprocal applied field obeyed the exponential law in the low-field region and the power law in the high-field region. The threshold field between the exponential law and the power law became monotonically lower with decreasing temperature. Furthermore, the exponent value in the power law increased with decreasing temperature. This seems to be caused by a change in domain growth from two-dimensional-like to three-dimensional-like or in nucleation mechanism with decreasing temperature.

High Temperature Thermoelectric Properties of Half-Heusler Compound PtYSb

Guanghe Li, Ken Kurosaki, Yuji Ohishi, Hiroaki Muta, and Shinsuke Yamanaka — 2013-04-03T09:00:00+09:00

Authors: Guanghe Li, Ken Kurosaki, Yuji Ohishi, Hiroaki Muta, and Shinsuke Yamanaka
Recent experimental examination of the thermoelectric properties of the half Heusler compound PtYSb has revealed that PtYSb has a relatively high thermoelectric figure of merit (ZT) of 0.2 at around room temperature. However, the thermoelectric properties have been examined only in the low-temperature region, and no high-temperature data has been reported to date. Here we present the high-temperature thermoelectric properties of polycrystalline bulk samples of PtYSb in the temperature range between room temperature and 973 K. The Seebeck coefficient was positive over the entire temperature range examined. A high power factor (2.1×10^{-3} W m^{-1} K^{-2}) and low thermal conductivity (3.44 W m^{-1} K^{-1}) were obtained at 973 K, which resulted in a relatively high ZT of 0.57 for PtYSb. Thus, PtYSb has the potential for application as a p-type thermoelectric material at high temperature.

Effect of Target Surface Microstructure on Morphological and Electrical Properties of Pulsed-Laser-Deposited BiFeO_{3} Epitaxial Thin Films

Katsuya Ujimoto, Takeshi Yoshimura, Atsushi Ashida, and Norifumi Fujimura — 2013-04-03T09:00:00+09:00

Authors: Katsuya Ujimoto, Takeshi Yoshimura, Atsushi Ashida, and Norifumi Fujimura
The effect of target surface microstructure on the morphological and electrical properties was studied on pulsed-laser-deposited lead-free ferroelectric BiFeO_{3} with a relatively low energy gap of about 2.7 eV and a high absorption coefficient of about 10^{5} cm^{-1} among ferroelectric materials. It was found that a columnar structure was formed on the target surface during the deposition and that droplet density increased when the columnar structure formed. We modified the driving system for the target to prevent the formation of the columnar structure. With the use of the target driving system, droplet density decreased to 42% relative to that without the use of the system. The effects of the morphology change of the target on the growth and electrical properties of BiFeO_{3} epitaxial films were also investigated. With the introduction of the system, breakdown voltage increased from 140 to 290 kV/cm and coercive field decreased from 112 to 82 kV/cm.

Quantitative and Fingerprint Analysis Method of Nitrogen in Graphitic Carbon Materials Using Total-Electron-Yield Soft X-ray Absorption Spectroscopy

Taiji Amano, Kensuke Shirode, Yasuji Muramatsu, and Eric M. Gullikson — 2013-04-02T09:00:00+09:00

Authors: Taiji Amano, Kensuke Shirode, Yasuji Muramatsu, and Eric M. Gullikson
To evaluate nitrogen in graphitic carbon materials, we propose a simple quantitative and fingerprint analysis method, which measures the total electron yield X-ray absorption spectra (TEY-XAS) of aromatic compounds possessing typical nitrogenated functional groups as standard samples, and fingerprint analysis is performed using the X-ray absorption near edge structure (XANES) in the N K and C K regions. The relationship between the atomic ratio of nitrogen to carbon (N/C) and the X-ray absorption intensity ratio of N K edge to C K edge (N Kσ^{*}/C Kσ^{*}) of standard samples yields a working curve to quantitatively analyze nitrogen. The successful application to carbon nitride films demonstrates that the proposed method is capable of quantitative and fingerprint analysis.

Effect of Defocusing on Ablated Volume of Gadolinium Oxide

2013-04-02T09:00:00+09:00

Authors: Masaki Oba, Yoichiro Maruyama, Katsuaki Akaoka, Masabumi Miyabe, and Ikuo Wakaida
We used nanosecond (ns) and femtosecond (fs) laser pulses to ablate gadolinium oxide samples and measured the ablated volume as a function of the laser pulse focal position. The effect of defocusing on the ablated volume, which decreases as the ablation pulse focal position approaches the sample surface, was observed for both ns and fs pulses.

Liquid Crystal Gratings with Twisted Alignment Produced by One-Step Polarizer-Rotation Exposure on Photocrosslinkable Polymer Liquid Crystal Films

2013-04-02T09:00:00+09:00

Authors: Tomoyuki Sasaki, Mitsuru Kuzuwata, Kohei Noda, Nobuhiro Kawatsuki, and Hiroshi Ono
Liquid crystal (LC) gratings with twisted alignment were fabricated by simple one-step polarizer-rotation exposure. An empty glass cell coated with photocrosslinkable polymer liquid crystal (PCLC) films was exposed by UV light with modulation of intensity or polarization. LC grating cells were obtained by filling the resultant cells with a nematic LC and the LC alignment structures were well controlled by both the intensity and polarization of the UV light. The diffraction properties of the LC gratings were explained by considering the periodic director distribution in the cells, estimated based on the elastic continuum theory of nematic LCs and the photoalignment effects of the PCLC films.

A Two-Dimensional Analytical Model for Tunnel Field Effect Transistor and Its Applications

Ning Cui, Libin Liu, Qian Xie, Zhen Tan, Renrong Liang, Jing Wang, and Jun Xu — 2013-04-02T09:00:00+09:00

Authors: Ning Cui, Libin Liu, Qian Xie, Zhen Tan, Renrong Liang, Jing Wang, and Jun Xu
In this paper, a two-dimensional analytical model for the tunnel field effect transistor (TFET) on the silicon-on-insulator substrate is proposed. The accurate electrostatic potential and electric field of the device are obtained by solving the Poisson equation with appropriate boundary conditions. The accuracy of the proposed analytical model is verified by comparing with numerical simulation. It is shown that the electrical behavior of the TFET is more properly described by defining the zero vertical electric field at the channel/buried oxide interface. Furthermore, this analytical model is extended to implement in the hetero-material-gate (HMG) TFET. The physical principle of the HMG TFET can also be depicted, and electrical properties are characterized using this model.

Design and Implementation of Wide-Angular Universal Broadband Visible Antireflection Coating for Various Substrates

Yeuh-Yeong Liou, En-Wei Chang, Li-Hsiang Kuo, and Cheng-Chung Jaing — 2013-04-01T09:00:00+09:00

Authors: Yeuh-Yeong Liou, En-Wei Chang, Li-Hsiang Kuo, and Cheng-Chung Jaing
We proposed a simple design method based on a scanning search algorithm for obtaining an acceptable wide-angular universal visible (vis) antireflection (AR) coating design with the incident angles over the range 0–30° for different glass substrates having refractive indices ranging from 1.472 to 1.750. We then applied AR-coating to seven different glass substrates in the same deposition run using ion-assisted deposition. It was shown that the measured and calculated wide-angular universal vis AR effects were in agreement, where the total average vis reflectances at angles 0 and 30° for the practical AR-coated substrates can be effectively reduced from 5.92 and 6.09% (uncoated substrates) to below 0.25 and 0.34%, respectively, which are comparable to the calculated reflectance values of 0.22 and 0.33%, revealing that an acceptable wide-angular universal vis AR performance can be obtained.

Impact of the Electrical Forming Process on the Resistance Switching Behaviors in Lanthanum-Doped Strontium Titanate Ceramic Chip Devices

2013-04-01T09:00:00+09:00

Authors: Sakyo Hirose, Hideaki Niimi, Keisuke Kageyama, Akira Ando, Hideharu Ieki, and Takahisa Omata
The resistance switching (RS) behaviors of La-doped SrTiO_{3} ceramics before and after the electrical forming process (E-forming) have been investigated in order to clarify the RS mechanism. The formation processes for the double Schottky barriers (DSBs), such as reoxidation and E-forming, are important to realize stable RS properties, and Joule heating strongly influences the RS behaviors after the E-forming. Thermally stimulated current measurements clearly indicated the contribution of defects related to oxygen vacancies to the current conduction through DSBs and RS phenomena both before and after the E-forming. Experimental results suggest that the electron trapping in the defects and/or the defect migration induced by the voltage application and Joule heating change the space-charge distribution near the grain boundaries, resulting in the change in the resistance state.

Kinetic Analysis of Dielectric Layer Thickness on Nitric Oxide Removal by Dielectric Barrier Discharge

Tao Wang, Bao-min Sun, and Hai-ping Xiao — 2013-04-01T09:00:00+09:00

Authors: Tao Wang, Bao-min Sun, and Hai-ping Xiao
The kinetic analysis of dielectric layer thickness on nitric oxide (NO) removal in dielectric barrier discharge (DBD) reactor was investigated. The simulated results show that, with the decrease of dielectric layer thickness, the electric field increases, leading to an enlarging E/N. When E/N was 250 Td, the dissociation rate and electron mean energy reached 14.3 times and 1.5 times respectively compared to when E/N was 150 Td, and their excitation rates were magnified 176, 182, 226, and 171% separately, generating more N atoms and metastable states of N_{2} molecules. In NO/N_{2} system, the dissociation and excitation rate of N_{2} were related to the amount of NO removal. The experimental results show that, NO removal efficiency increased as energy density was increased and a decreasing dielectric layer thickness promoted NO removal, which coincides with simulated ones well, indicating the feasibility and the rationality of the dynamics analysis.

Unique ZnS–SiO_{2} Morphologies Reflecting a Laser-Induced Heat Distribution

Tetsuji Mori and Masahide Itoh — 2013-04-01T09:00:00+09:00

Authors: Tetsuji Mori and Masahide Itoh
Unique morphologies including a hemispherical dot and an inverse trapezoid line were fabricated from a mixture of zinc sulfide (ZnS) and silicon dioxide (SiO_{2}) using thermal lithography. Depending on the laser power, three types of morphologies were formed for each of the dot and line patterns. The patterns were affected by the concentric heat transfer from the underlying light-absorption layer, and the transverse heat transfer caused by the spatial restriction. These unique morphologies are difficult to fabricate using photolithography, and they are therefore promising for new functional applications involving microscale structures.

Enhanced Light Emission of Light-Emitting Diodes with Silicon Oxide Nanobowls Photonic Crystal without Electrical Performance Damages

2013-03-29T09:00:00+09:00

Authors: Chengxiao Du, Chong Geng, Haiyang Zheng, Tongbo Wei, Yu Chen, Yiyun Zhang, Kui Wu, Qingfeng Yan, Junxi Wang, and Jinmin Li
Unencapsulated GaN-based light-emitting diodes (LEDs) with two-dimensional (2D) hexagonal closely-packed silicon oxide nanobowls photonic crystal (PhC) on the indium tin oxide (ITO) transparent conductive layer were fabricated by using polystyrene spheres and sol–gel process. Compared to conventional LEDs with planar ITO layers, the light output power of 600-nm-lattice PhC LEDs was improved by 25.6% at an injection current of 20 mA. Furthermore, electrical performance of the PhC LEDs was damage-free via this chemical technique.

Origin of the Improved Power Conversion Efficiency of Pentacene/C_{60} Heterojunction Photovoltaic Devices through the Purification of Donor Material

2013-03-29T09:00:00+09:00

Authors: Shun-Wei Liu, Wei-Cheng Su, Chih-Chien Lee, Ching-Wen Cheng, Chia-Chang Chou, and Chun-Feng Lin
The authors report the impact of the crystallinity property of the electron donor on the performance of a pentacene/C_{60} organic photovoltaic device. After subjecting pentacene to sublimation twice, all the photovoltaic parameters showed significant improvements leading to enhancement of the power conversion efficiency from 0.9 to 2.2% under air mass 1.5G solar illumination. This is attributed to the well-packed molecular structure in the pentacene thin film, as observed by X-ray diffraction, which leads to high carrier mobility and hence high photocurrent. Moreover, the elimination of microscopic pinholes or defect sites due to the improvement in the degree of the pentacene thin film reduces the dark current and therefore increases the photovoltage. The external quantum efficiency and space-charge limited current are used to analyze the relationship between the quality of thin film electron donor and device performance.

Detailed Impurity Phase Investigation by X-ray Absorption Fine Structure and Electron Spin Resonance Analyses in Synthesis of CaMgSi_{2}O_{6}:Eu Phosphor

Takashi Kunimoto, Tetsuo Honma, Koutoku Ohmi, Susumu Okubo, and Hitoshi Ohta — 2013-03-29T09:00:00+09:00

Authors: Takashi Kunimoto, Tetsuo Honma, Koutoku Ohmi, Susumu Okubo, and Hitoshi Ohta
Impurity phases of CaMgSi_{2}O_{6}:Eu (CMS) phosphor have been investigated in detail by X-ray absorption fine structure (XAFS), ESR, X-ray diffraction (XRD) and photoluminescence (PL) analyses. XRD studies of CMS phosphor powders clarify the volume fraction of CMS, Ca_{2}MgSi_{2}O_{7}, (Ca,Eu)_{10}(SiO_{4})_{6}O_{2}, and crystalline SiO_{2}. XAFS and ESR studies clarify that the soluble limit of Eu ions in CMS crystals is observed at about 0.01 mol. Excess Eu ions yield an impurity (Ca,Eu)_{10}(SiO_{4})_{6}O_{2} and some of them are captured by another impurity Ca_{2}MgSi_{2}O_{7}. From the results of XAFS, ESR, XRD, and PL measurements, it was revealed that the PL peak intensities under 147 and 360 nm excitation correlate closely with the amount of these impurity phases containing divalent and trivalent Eu ions. Variation of X-ray absorption near edge structure and ESR spectra indicate that the optimum Eu concentration of the CMS phosphor is at approximately 0.01 molar versus Ca.

Resistive Switching in Conductive-Bridging Random-Access Memory Structure with Nanocrystalline Silicon Films

Jian-Yang Lin and Bing-Xun Wang — 2013-03-29T09:00:00+09:00

Authors: Jian-Yang Lin and Bing-Xun Wang
In this work, intrinsic nanocrystalline silicon thin films were deposited on indium tin oxide/glass substrates by plasma-enhanced chemical vapor deposition and used as a conduction material for conductive-bridging random-access memory devices. The resistive switching characteristics of nanocrystalline silicon thin films were investigated. Experimental results show a stable bipolar resistive switching of the nanocrystalline silicon films with a retention time of over 1×10^{4} s. In addition, the current conduction mechanism of the nanocrystalline silicon films was examined by X-ray photoelectron spectroscopy depth profiling and transmission electron microscopy analysis. Results clearly indicate that the conduction mechanism for resistive switching is the formation of metallic bridges due to the metal cation migration in the nanocrystalline silicon films.

Channel Length Scaling Effects on Device Performance of Junctionless Field-Effect Transistor

Katsuyuki Nagai, Hideaki Tsuchiya, and Matsuto Ogawa — 2013-03-27T09:00:00+09:00

Authors: Katsuyuki Nagai, Hideaki Tsuchiya, and Matsuto Ogawa
We study channel length scaling effects on the device performance of junctionless field-effect transistors, based on a Monte Carlo approach. We found that impurity scattering due to ionized donors in the channel significantly decreases the drain current at a small gate overdrive for a long channel device, but the influence of impurity scattering gradually disappears on reducing the channel length. We discuss the mechanism behind these behaviors in terms of an increasing importance of the forward-scattering nature of ionized impurities in accordance with the channel length scaling.

Epitaxial Growth of ZnTe Layers on ZnO Bulk Substrates by Metalorganic Vapor Phase Epitaxy

2013-03-25T09:00:00+09:00

Authors: Hajime Akiyama, Hiroyuki Hirano, Katsuhiko Saito, Tooru Tanaka, Mitsuhiro Nishio, and Qixin Guo
The crystallinity and surface roughness of ZnTe epilayers grown on (0001) ZnO bulk substrates by metal organic vapor phase epitaxy are investigated. X-ray diffraction, Raman spectra, photoluminescence, and atomic force microscopy analysis results prove that the crystallinity and surface roughness of ZnTe epilayers depend on epitaxial growth temperature. A high-crystal-quality (111) ZnTe heteroepitaxial layer, with near-band-edge emission at 549 nm, was obtained at a substrate temperature of 460 °C.

Effects of Hf Incorporation on Negative Bias-Illumination Stress Stability in Hf–In–Zn–O Thin-Film Transistors

Sangwook Kim, Jae Chul Park, Dae Hwan Kim, and Jang-Sik Lee — 2013-03-25T09:00:00+09:00

Authors: Sangwook Kim, Jae Chul Park, Dae Hwan Kim, and Jang-Sik Lee
In this study, highly reliable amorphous oxide semiconductor-based thin-film transistors (TFTs) were developed. The Hf concentration was systematically changed in the Hf-incorporated In–Zn–O (HIZO) TFTs, and Hf played an important role in determining the negative bias-illumination instability. The process parameters were optimized in order to obtain HIZO TFTs with an excellent stability. HIZO can be processed on a 6-in. wafer at low temperatures and is almost transparent in the visible range. Thus this material is promising for use in current TFTs as well as future transparent electronic device components with good electrical performance and excellent stability.

Determination of Aluminium Mole Fraction in AlGaN Layers of GaN-Capped AlGaN/GaN Heteroepitaxial Wafers by Ultraviolet Reflection

Yoshihata Yanase, Hiroshi Shirai, and Jun Komiyama — 2013-03-25T09:00:00+09:00

Authors: Yoshihata Yanase, Hiroshi Shirai, and Jun Komiyama
Ultraviolet reflection spectroscopy is applicable to the determination of the aluminium mole fraction of GaN-capped AlGaN/GaN heteroepitaxial wafers on silicon, while conventional photoluminescence is inapplicable. AlGaN peaks in the ultraviolet reflection spectra are clearly observed regardless of the cap, but the AlGaN photoluminescence peaks of the samples with a 2-nm-thick cap are difficult to observe clearly. For some capped samples, the quantum-well emission due to the cap is observed near the AlGaN peak.

Determined Optical Constants of ZnSe Glass from 0.83 to 21 µm by Transmittance Spectra: Methods and Measurements

Dong Li, Qing Ai, and Xinlin Xia — 2013-03-22T09:00:00+09:00

Authors: Dong Li, Qing Ai, and Xinlin Xia
Based on the transmittance spectra modeling, spectroscopic methods were developed to determine the optical constants of glass materials including extinction coefficient and refractive index. The transmittance spectrograms of ZnSe glass slabs at normal incidence with different thicknesses in the infrared wavelength 0.83–21 µm were measured by a Bruke V70 Fourier transform infrared (FTIR) spectrometer. These values were introduced into spectroscopic methods to calculate the optical constants of ZnSe glass. The results showed most of the optical constants of ZnSe determined by the new method had a good agreement with previously data, indicating that the spectroscopic methods can be used to determine the optical constants of glass materials in most infrared spectra.

Electrokinetic Delivery of Biomolecules into Living Cells for Analysis of Cellular Regulation

2013-03-22T09:00:00+09:00

Authors: Moeto Nagai, Tatsuro Torimoto, Tokuma Miyamoto, Takahiro Kawashima, and Takayuki Shibata
Current biomolecule-delivery systems, which function via pressure-driven flow, possess several significant limitations. We herein present a novel delivery method for biomolecules based on electrokinetic flow. The electrokinetic flow method uses capillaries to more easily deliver solutions than the pressure-driven flow method, which enables controllable injection of biomolecules into living cells. We characterized the electrokinetic flow of molecules to determine the parameters required for reproducible injections. Then, we successfully demonstrated the electrokinetic injection of a fluorescent DNA and dye solution into a living HeLa cell through a glass needle (1 µm in diameter). The monitoring of changes in ion current during the delivery process also allowed for the precise detection of penetration through the cell membrane with the tip of the needle.

Spin Relaxation in Weak Localization Regime in Multilayer Graphene Spin Valves

2013-03-21T09:00:00+09:00

Authors: Takehiro Yamaguchi, Rai Moriya, Satoru Masubuchi, Kazuyuki Iguchi, and Tomoki Machida
The temperature dependence of the spin relaxation time τ_{s} in multilayer graphene (MLG) spin valve devices was measured using a non-local magnetoresistance (NLMR) measurement. A weak localization (WL) was observed from magnetoresistance (MR) measurements below ∼70 K, suggesting coherent transport of the charge carriers. Within the same temperature range, we observed a large increase in the spin relaxation time τ_{s} and spin diffusion length λ_{s} even though the diffusion constant D_{s} was suppressed by the WL. This demonstrated that the spin relaxation time in MLG could be significantly extended when the charge experiences quantum interference effect in the coherent charge transport regime.

Simple Scanning Phase-Contrast X-ray Tomography Using Intensity Detectors

2013-03-19T09:00:00+09:00

Authors: Hidekazu Takano, Sho Shimomura, Shigeki Konishi, Hiroaki Azuma, Yoshiyuki Tsusaka, and Yasushi Kagoshima
We have developed a phase-contrast X-ray microtomography system based on scanning microscopy with X-ray focusing optics. The system is very simple because only two conventional intensity detectors and a half-obstructing-plate for the second detector are installed into the conventional scanning microscopy setup. We constructed the system with a 450-nm-size focused beam of a 10 keV X-ray. The system is operated with a sampling rate of 100 Hz. Adopting data correction using a guide object and data interpolation procedure in sinograms, tomographic reconstruction images with a high spatial resolution and phase sensitivity are obtained.

Minority Carrier Annihilation in Lateral Direction Caused by Recombination Defects at Cut Edges and Bear Surfaces of Crystalline Silicon

Toshiyuki Sameshima, Jun Furukawa, and Shinya Yoshidomi — 2013-03-19T09:00:00+09:00

Authors: Toshiyuki Sameshima, Jun Furukawa, and Shinya Yoshidomi
We report on the photo-induced minority carrier annihilation effect in the lateral direction caused by cut edges and partially formed bare surfaces for 500-µm-thick n-type silicon substrates coated with thermally grown SiO_{2} layers. A 9.35 GHz microwave transmittance measurement system with illumination with a 0.2-cm-wide 635-nm continuous wave light beam was used to measure spatial distribution of the minority carrier effective lifetime τ_{eff}. A mechanical cut decreased τ_{eff} in a 0.9-cm-wide region from the cut edges. τ_{eff} decreased from 3.4×10^{-3} (initial) to 6.5×10^{-4} s at cut edges. A simple model of carrier diffusion in the lateral direction with a carrier lifetime of 3.4×10^{-3} s and a recombination velocity of 500 cm/s at the cut edges well explained the experimental spatial change in τ_{eff} near the cut edges. A similar widely spatial decrease in τ_{eff} was also observed in the region coated with thermally grown SiO_{2} layers near the bare silicon surface formed by partial etching of SiO_{2}.

Lifetime of Poly(triaryl amine) Based Organic Field Effect Transistors under Different Environmental Conditions

Tobias Lau, Enno Lorenz, and Metin Koyuncu — 2013-03-18T09:00:00+09:00

Authors: Tobias Lau, Enno Lorenz, and Metin Koyuncu
Characterization of reliability and lifetime is a key issue on the way to commercialization of products based on organic electronics. Prediction of the lifetime requires the understanding of failure mechanisms and the circumstances leading to failure. In this work the stability of poly(triaryl amine) (PTAA) based organic field effect transistors (OFETs) on a poly(ethylene naphthalate) (PEN) substrate is investigated under environmental stressing. PTAA is known to form amorphous thin films after spin coating and to be air stable for extended periods of time. This inherent air stability makes it a good candidate for testing of environmental influences. The samples were electrically characterized regularly between storage cycles at 85 °C and 85 °C/85% relative humidity (RH). Samples stored under dry atmosphere and inert gas were used as reference. More than 1700 OFETs were produced in multiple batches and measured using an automated measurement system to collect statistically significant data. Circuit-relevant OFET parameters such as on- and off-current, mobility, threshold voltage and gate leakage current were extracted applying a thin film transistor (TFT) device model to the measured transfer and output curves. The threshold voltage is found to be the most sensitive parameter especially for the samples stored at 85 °C. The effect of storage under 85 °C/85%RH is observed to be comparably small. Fourier transform infrared (FT-IR) measurements of the aged OFET samples indicate a correlation between the shift of the electrical parameters and the appearance of carbonyl groups in the dielectric layer of the devices. Possible degradation mechanisms are discussed based on this observation.

Direct Observation of Au Nanoclusters at Au/Si Interface and Enhanced SiO_{2} Growth Due to Catalytic Action by Au in Thermally Oxidized Au-Precipitated n-Type Si(001) Surfaces

Hirofumi Shimizu, Akihito Kumamoto, and Senji Imamura — 2013-03-18T09:00:00+09:00

Authors: Hirofumi Shimizu, Akihito Kumamoto, and Senji Imamura
The behavior of Au nanoclusters at a Au/n-Si interface was investigated. In particular, SiO_{2} growth in thermally oxidized Au-precipitated n-type Si(001) surfaces was enhanced by the catalytic action of Au. When the Au-precipitated Si wafer was exposed to air for 30 d at room temperature (RT), a SiO_{2} film layer grew over Au nanoclusters on the Si surface. This is possibly because Si atoms may diffuse in an as-deposited Au layer and are oxidized in air at RT. In the case of oxidation at higher temperatures (850 °C for 30 min), Au nanoclusters were found to exist at the Au/n-Si interface. Moreover, the origin of protuberances observed by atomic force microscopy was found to be a bulge in the SiO_{2} film formed over the Au nanocluster, proving that the growth of the SiO_{2} film layer was enhanced by the catalytic action of Au.

First-Principles Studies of the Electronic and Dielectric Properties of Si/SiO_{2}/HfO_{2} Interfaces

Yongjin Park, Ki-jeong Kong, Hyunju Chang, and Mincheol Shin — 2013-03-18T09:00:00+09:00

Authors: Yongjin Park, Ki-jeong Kong, Hyunju Chang, and Mincheol Shin
In an effort to link first-principles electronic structure information with device-level modeling and simulations, first-principles calculations were performed to model Si/SiO_{2}/HfO_{2} gate stacks, and models of their interfaces were developed. The electronic and dielectric properties, including the band edge and the local dielectric constant profiles, were investigated and found to display non-abrupt transitions at the hetero-material boundaries. The first-principles equivalent oxide thickness (EOT) parameter was introduced to represent the overall dielectric characteristics of the gate stack. The role of defects in the oxides was investigated by performing first-principles calculations of a Si/SiO_{2}/HfO_{2} slab model with an oxygen vacancy near the SiO_{2}/HfO_{2} interface. The oxygen vacancy was found to reduce the EOT.

Time-Resolved Pump and Probe Experiment for Wide-Gap Semiconductors Using Free Electron Laser and Synchronously-Operated Femtosecond Laser

2013-03-15T09:00:00+09:00

Authors: Kohei Yamanoi, Toshihiko Shimizu, Marilou Cadatal-Raduban, Ryosuke Nishi, Kohei Takeda, Yuki Shinzato, Tomoharu Nakazato, Nobuhiko Sarukura, Tsuguo Fukuda, Mitsuru Nagasono, Tadashi Togashi, Takahiro Satoh, and Tetsuya Ishikawa
Pump–probe technique is an important means of studying the structure and dynamics of a single protein molecule. X-ray free electron lasers (XFELs) such as the Linac Coherent Light Source (LCLS) and SPring-8 Angstrom Compact free electron Laser (SACLA) provide the Angstrom-wavelength, high-intensity femtosecond pulses needed for revealing the structure of a single protein molecule without crystallization and for observing atomic motion during a chemical reaction via pump–probe experiments. In this paper, we demonstrated X-ray pump–optical probe and optical pump–X-ray probe experiments, creating new possibilities for time-resolved EUV spectroscopy of solid targets including wide-gap semiconductors such as gallium nitride.

Enhanced and Retarded SiO_{2} Growth on Thermally Oxidized Fe-Contaminated n-Type Si(001) Surfaces

Hirofumi Shimizu and Hiroyuki Hagiwara — 2013-03-15T09:00:00+09:00

Authors: Hirofumi Shimizu and Hiroyuki Hagiwara
At the beginning of the oxidation of Fe-contaminated n-type Si(001) surfaces, Fe reacted with oxygen (O_{2}) on the silicon (Si) substrate to form Fe_{2}O_{3} and oxygen-induced point defects (emitted Si + vacancies). SiO_{2} growth was mainly enhanced by catalytic action of Fe. At 650 °C, SiO_{2} growth of the contaminated samples was faster than in reference samples rinsed in RCA solution during the first 60 min. However, it substantially slowed and became less than that of the reference samples. As the oxidation advanced, approximately half of the contaminated Fe atoms became concentrated close to the surface area of the SiO_{2} film layer. This Fe_{2}O_{3}-rich SiO_{2} layer acted as a diffusion barrier against oxygen species. The diffusion of oxygen atoms toward the SiO_{2}/Si interface may have been reduced, and in turn, the emission of Si self-interstitials owing to oxidation-induced strain may have been decreased at the SiO_{2}/Si interface, resulting in the retarded oxide growth. These results are evidence that emitted Si self-interstitials are oxidized not in the Fe_{2}O_{3}-rich SiO_{2} layer, but at the SiO_{2}/Si interface in accordance with a previously proposed model. A possible mechanism based on the interfacial Si emission model is discussed. The activation energies for the oxide growth are found to be in accord with the enhanced and reduced growths of the Fe-contaminated samples.

Structural, Electronic, and Electrochemical Properties of Li_{x}Co[Fe(CN)_{6}]_{0.90}2.9H_{2}O

Masamitsu Takachi, Tomoyuki Matsuda, and Yutaka Moritomo — 2013-03-15T09:00:00+09:00

Authors: Masamitsu Takachi, Tomoyuki Matsuda, and Yutaka Moritomo
Prussian blue analogues with jungle-gym-type structure are promising candidates for cathode materials of the lithium-ion secondary battery (LIB). Here, we investigated the structural, electronic, and electrochemical properties of cobalt hexacyanoferrate, Li_{x}Co[Fe(CN)_{6}]_{0.90}2.9H_{2}O, against Li concentration (x). The capacity (= 139 mAh/g) of the thin-film electrode was close to the ideal value (= 132 mAh/g) for the two-electron reaction. The discharge curve exhibits three plateaus, i.e., plateaus I, II, and III. The material exhibits a first-order phase transition accompanied by significant volume expansion by 7% at the boundary between plateaus II and III. Ex situ X-ray absorption spectroscopy (XAS) indicates that the discharge processes of plateaus I, II, and III are ascribed to the reduction processes of Fe^{3+}, Co^{3+}, and Fe^{3+}, respectively. The rate (r) and cycle (n) dependence of the electrode performance will be discussed in terms of the reduction processes.

Fabrication and Evaluation of Thin-Film Spiral-Antenna-Coupled VO_{x} Microbolometer by Metal–Organic Decomposition

Le Ngoc Son, Takashi Tachiki, and Takashi Uchida — 2013-03-15T09:00:00+09:00

Authors: Le Ngoc Son, Takashi Tachiki, and Takashi Uchida
A VO_{x} microbolometer coupled with thin-film spiral antenna was fabricated on a fused-quartz substrate by metal–organic decomposition (MOD). The size of the bolometer was 1 ×52 µm^{2}, and the antenna was designed for operating at 75–110 GHz. The DC sensitivity and responsivity of the bolometer were 540 W^{-1} and 124 V/W at the bias current of 0.5 mA under the irradiation of a 94 GHz electromagnetic wave, respectively. These values were over one order higher than those of the Bi microbolometer, which is conventionally utilized as a detector in terahertz and infrared regions. The antenna-coupled VO_{x} microbolometer with a high responsivity was realized by MOD.

Titanium–Aluminum Bilayer Cathode for Small-Molecular Organic Solar Cells with Prolonged Life upon Exposure to Air

Huanqi Cao, Hideo Takezoe, and Ken Ishikawa — 2013-03-14T09:00:00+09:00

Authors: Huanqi Cao, Hideo Takezoe, and Ken Ishikawa
The in-air stability of unencapsulated small-molecular organic solar cells (OSCs) was improved by 3 orders of magnitude by using a Ti (inner)–Al (exposed to air) bilayer cathode, in comparison with that of Al-monolayer-cathode OSCs. The stability of the unencapsulated bilayer-cathode OSCs (AlTi-OSCs) was comparable to that of encapsulated ones. These devices were degradation-free in air for more than 3 months. Under weathering tests, the unencapsulated AlTi-OSCs recovered their performance in the idle periods. This provides us with an effective and economical approach to prevent degradation of the extensively studied aluminum-cathode OSCs.

Unipolar Resistive Switching in ZrO_{2} Thin Films

2013-03-14T09:00:00+09:00

Authors: Guo-Yong Zhang, Dai-Ying Lee, I-Chuan Yao, Chung-Jung Hung, Sheng-Yu Wang, Tai-Yuen Huang, Jia-Woei Wu, and Tseung-Yuen Tseng
Unipolar resistive switching behaviors including bistable memory switching and monostable threshold switching were found in ZrO_{2} thin films fabricated by a simple sol–gel method with the Ti/ZrO_{2}/Pt structure. The multilevel resistive switching behaviors were also revealed by varying the compliance current from 9 to 38 mA. Physical mechanisms based on a conductive filament model were proposed to explain the resistive switching phenomena and the device breakdown. A figure of merit Z = ρ_{a}/ρ_{f} was defined as a criterion for evaluating OFF/ON resistance ratio, where ρ_{f} and ρ_{a} represent the resistivities of the conductive filament and the fracture region of the filament, respectively. The advantages such as unipolar resistive switching, multilevel resistive switching, good scalability, low operation voltage (<5 V), high OFF/ON resistance ratio (>10^{3}), nondestructive readout, long retention (>10^{4} s), and simple fabrication method make the ZrO_{2}-based resistive switching device a promising candidate for next-generation nonvolatile memory applications.

Microscopic Investigation of the Electrical and Structural Properties of Conductive Filaments Formed in Pt/NiO/Pt Resistive Switching Cells

Tatsuya Iwata, Yusuke Nishi, and Tsunenobu Kimoto — 2013-03-14T09:00:00+09:00

Authors: Tatsuya Iwata, Yusuke Nishi, and Tsunenobu Kimoto
Conductive filaments formed in Pt/NiO/Pt resistive switching (RS) cells were characterized by conductive atomic force microscopy (C-AFM) and cross-sectional transmission electron microscopy (XTEM) after the removal of top electrodes. The area and current of the filaments were directly detected by C-AFM. By examining various RS cells with different cell resistances in the low-resistance state (R_{LRS}), it has been revealed that the R_{LRS} variation in the range of 10–220 Ω is mainly caused by the variations in the area and shape of the filaments. XTEM was carried out on a filament that dominantly determines R_{LRS}. The area of the filament significantly varied along the thickness direction of a NiO film, which was consistent with the speculation from C-AFM analysis. Furthermore, the filaments observed in this study consist of reduced NiO with an inclusion of platinum, the electrode material, owing to Joule heating by the current during forming.

Chemical Gradient of Contact Hole Latent Image Created in Chemically Amplified Extreme Ultraviolet Resists

Takahiro Kozawa and Taku Hirayama — 2013-03-14T09:00:00+09:00

Authors: Takahiro Kozawa and Taku Hirayama
A contact hole pattern as well as a line-and-space pattern is a basic element for the fabrication of semiconductor devices. The critical dimension uniformity and edge roughness of contact hole patterns are critical issues for extreme ultraviolet (EUV) lithography. In this study, the quality of the latent images of contact hole patterns was investigated in terms of the chemical gradient using a simulation on the basis of the reaction mechanisms of chemically amplified EUV resists. The latent image formation of contact hole patterns was compared with that of line-and-space patterns. The latent image quality of contact hole patterns was significantly lower than that of line-and-space patterns. To obtain the same latent image quality as line-and-space patterns, the exposure dose should be increased 1.4±0.1 times. Similarly to the line-and-space patterns, the increase of acid generator concentration and effective reaction radius is effective for the enhancement of latent image quality. For the enhancement of latent image quality of contact hole patterns, the enhancement of the effective reaction radius is more effective in a low exposure dose region than a high exposure dose region.

Fabrication of Silicon Microchannel for Transport of Bacterial Cells by Ar/F_{2} Vapor Etching Process

Akihiro Matsutani and Ayako Takada — 2013-03-14T09:00:00+09:00

Authors: Akihiro Matsutani and Ayako Takada
We fabricated a Si based microchannel without cover plates by an Ar/F_{2} vapor etching process. In the Ar/F_{2} vapor etching process, the Si substrate was etched in proportion to the etching time with good controllability. We succeeded in the transport of Escherichia coli cells in the microchannel. In addition, we fabricated a Si-based two-step microchannel without cover plates by Ar/F_{2} vapor etching and Cl_{2}-based inductively coupled plasma (ICP) etching processes. The proposed microchannel would be useful for the separation of bacterial cells according to size.

Effects of Process Parameters on Replication Accuracy of Microinjection Molded Cyclic Olefins Copolymers Parts

2013-03-13T09:00:00+09:00

Authors: Hsuan-Liang Lin, Chun-Sheng Chen, Ruey-Tsung Lee, Shia-Chung Chen, Rean-Der Chien, Ming-Chang Jeng, and Jiun-Ren Hwang
In this study, the effects of various processing parameters of microinjection molding on the replication accuracy of the micro featured fluidic platform used for DNA/RNA tests are investigated. LIGA-like processes were utilized to prepare a silicon-based SU-8 photoresist, followed by electroforming to make a Ni–Co-based stamp. A cyclic olefin copolymer (COC) was used as the injection molding material. The molding parameters associated with the replication accuracy of micro channel parts were investigated. It was found that for microinjection molded devices, the replication accuracies of the imprint width and depth increase with increasing of mold temperature, melt temperature, injection velocity, and packing pressure.

Thermodynamic Analysis of Coherently Grown GaAsN/Ge: Effects of Different Gaseous Sources

2013-03-13T09:00:00+09:00

Authors: Jun Kawano, Yoshihiro Kangawa, Tomoe Yayama, Koichi Kakimoto, and Akinori Koukitu
Thermodynamic analysis of coherently grown GaAs_{1-x}N_{x} on Ge with low N content was performed to determine the relationship between solid composition and growth conditions. In this study, a new algorithm for the simulation code, which is applicable to wider combinations of gaseous sources than the traditional algorithm, was developed to determine the influence of different gaseous sources on N incorporation. Using this code, here we successfully compared two cases: one is a system using trimethylgallium (TMG), AsH_{3}, and NH_{3}, and the other uses dimethylhydrazine (DMHy) instead of NH_{3}. It was found that the optimal N/As ratio of input gas in the system using DMHy was much lower than that using NH_{3}. This shows that the newly developed algorithm could be a useful tool for analyzing the N incorporation during the vapor growth of GaAs_{1-x}N_{x}.

X-ray Absorption Studies on the Growth Process of Radio-Frequency-Magnetron-Sputtered Boron Nitride Films: Effects of Bias Voltage and Substrate Temperature

2013-03-13T09:00:00+09:00

Authors: Satoko Hori, Masahito Niibe, Takuya Kotaka, Kiyotoshi Fujii, Keisuke Yoshiki, Takahiro Namazu, and Shozo Inoue
We have investigated the effects of bias voltage and substrate temperature on the growth process of RF-magnetron-sputtered BN films. When the negative bias voltage was higher than 80 V, films including the sp^{3}-BN phase grew even if the substrate temperature was RT. When the substrate temperature and the negative bias voltage were 600 °C and >100 V, respectively, films containing more than 90% sp^{3}-BN phase were grown. The growth process of films deposited at 150 and 600 °C under a constant bias voltage of -100 V was studied by Near edge X-ray absorption fine structure (NEXAFS) measurements. These films consisted of two layers: an sp^{2}-BN phase underlayer and an sp^{3}-BN phase top layer. The sp^{2}-BN underlayer had a preferential orientation of the c-axis parallel to the film surface. The thickness of the sp^{2}-BN underlayer decreased with increasing substrate temperature. High substrate temperatures assisted the nucleation and growth of the sp^{3}-BN phase.

Effect of Hydrogen on Vacancy Formation in Sputtered Cu Films Studied by Positron Annihilation Spectroscopy

2013-03-13T09:00:00+09:00

Authors: Atsushi Yabuuchi, Teruo Kihara, Daichi Kubo, Masataka Mizuno, Hideki Araki, Takashi Onishi, and Yasuharu Shirai
As a part of the LSI interconnect fabrication process, a post-deposition high-pressure annealing process is proposed for embedding copper into trench structures. The embedding property of sputtered Cu films has been recognized to be improved by adding hydrogen to the sputtering argon gas. In this study, to elucidate the effect of hydrogen on vacancy formation in sputtered Cu films, normal argon-sputtered and argon–hydrogen-sputtered Cu films were evaluated by positron annihilation spectroscopy. As a result, monovacancies with a concentration of more than 10^{-4} were observed in the argon–hydrogen-sputtered Cu films, whereas only one positron lifetime component corresponding to the grain boundary was detected in the normal argon-sputtered Cu films. This result means monovacancies are stabilized by adding hydrogen to sputtering gas. In the annealing process, the stabilized monovacancies began clustering at around 300 °C, which indicates the dissociation of monovacancy-hydrogen bonds. The introduced monovacancies may promote creep deformation during high-pressure annealing.

Characterization of Single-Crystalline Aluminum Thin Film on (100) GaAs Substrate

2013-03-12T09:00:00+09:00

Authors: Shi-Wei Lin, Jau-Yang Wu, Sheng-Di Lin, Ming-Cheng Lo, Ming-Huei Lin, and Chi-Te Liang
We have studied the structure and physical properties of an aluminum thin film grown on a (100) GaAs substrate. The X-ray diffraction (XRD) data shows that the Al film grown in situ by molecular beam epitaxy (MBE) is single crystalline. Compared with the polycrystalline film ex situ evaporated using an electron-gun (E-gun), the MBE-grown Al film has a high optical reflectivity in the visible and ultraviolet (UV) regime. In addition, the MBE-grown film has a 2-order-lower residue resistance, a 1-order-higher temperature coefficient of resistance, and a 2-order-larger magnetoresistance (MR) than the polycrystalline film. Owing to the long mean free time, the bulk-like electron-to-hole transition of Hall resistivity is observed for the first time in a nanoscale metal thin film. Our results suggest that MBE-grown Al thin films have great potential applications in metal-based nanoelectronics and nanophotonics.

Optical-Fiber-Type Broadband Cavity Ring-Down Spectroscopy Using Wavelength-Tunable Ultrashort Pulsed Light

2013-03-11T09:00:00+09:00

Authors: Takehiro Hiraoka, Takayuki Ohta, Masafumi Ito, Norihiko Nishizawa, and Masaru Hori
We proposed an optical-fiber-type broadband cavity ring-down spectroscopy system using wavelength-tunable ultrashort pulsed light. The absorbance of glucose in various concentrations in water was derived from the ring-down plots of intensities of the interference waveforms generated using a Mach–Zehnder interferometer with different optical delay path lengths, which were shifted by an automatic optical switching module. The absorption spectrum of glucose was obtained in the wavelength region from 1620 to 1690 nm by varying the wavelength using wavelength-tunable ultrashort pulsed light, which was generated from a femtosecond pulsed laser and polarization-maintaining fiber. The measurement error of concentration was improved using multiple linear regression analysis of absorption spectra. The results demonstrate that the optical-fiber-type cavity ring-down spectroscopy system has the potential to measure broadband absorption spectra with high sensitivity.

Interface Nature of Ordered Thermally Oxidized Si Nanowires Probed by Electron Spin Resonance: Post Fabrication Annealing and Irradiation

2013-03-11T09:00:00+09:00

Authors: Mihaela Jiv\uanescu, Andre Stesmans, Rufi Kurstjens, and Frédéric Dross
Extensive low-temperature (T) electron spin resonance studies (ESR) have been carried out on as-fabricated, vacuum annealed, and irradiated single crystalline arrays of Si nanowires (NWs) with a top diameter of 5 nm produced by top down etching into (100)Si, finally thinned down by high-T oxidation. This reveals the presence of a substantial inherent density of P_{b0} (Si_{3}≡Si^{•}) interface defects (charge trapping and recombination centers) quite above standard thermal values, leaving NW-Si/SiO_{2} interfaces of reduced electrical quality with, consequently, negative influence on the efficiency of passivation of defects by H. The inherent interface quality appears limited by the wire-narrowing thermal oxidation procedure. Vacuum annealing (≈610 °C) is found to generally reduce, to more or lesser extent, the P_{b0} density to a common value over all samples studied, which result directly counters the presence of inadvertent passivation of defects by H. Rather, the anneal appears to effectuate some interface healing. Short term (\lesssim2 h) UV and VUV (10.02 eV) irradiation has little effect in general, with perhaps some weak increase of P_{b1} defects induced by UV photons. On the basis of the observed E'_{γ} defect properties, the chemical vapor deposited Si NW inter space filling Si oxide (200 °C) is found to be OH enriched.

Accurate Complex Refractive Index with Standard Deviation of ZnTe Measured by Terahertz Time Domain Spectroscopy

2013-03-11T09:00:00+09:00

Authors: Saroj R. Tripathi, Makoto Aoki, Masanori Takeda, Toshiaki Asahi, Iwao Hosako, and Norihisa Hiromoto
Accurate complex refractive index of ZnTe crystal in terahertz spectral region from 0.2 to 3.5 THz is obtained by measuring three samples with different thickness using transmission terahertz time-domain spectroscopy. Each sample is measured a number of times and the mean and standard deviation (SD) of the complex refractive index are calculated to quantify the random errors in the measurement. The ratios of SD to mean of the real and imaginary parts of the refractive index are approximately 1.0×10^{-4} and 1.2×10^{-2} at 1 THz respectively. The absorption coefficient of our ZnTe sample is found to be comparable with or smaller than the values reported in previous literatures.

Measurement of Optical Aberrations of Liquid Crystal Lens

2013-03-11T09:00:00+09:00

Authors: Mao Ye, Bin Wang, Masaru Uchida, Satoshi Yanase, Hiroaki Kunitsuka, Shingo Takahashi, and Susumu Sato
The dependences of the optical aberrations of the recently proposed low-voltage-driving liquid crystal lens on the amplitudes and frequency of the driving voltages are studied. The analysis results of the root mean square aberration of the lens suggest driving parameters that ensure both low aberrations and a wide focus range.

Phase-Contrast X-ray Images of Ice and Water on Carbon Paper for Fuel Cells Measured by Diffraction-Enhanced Imaging Technique

2013-03-11T09:00:00+09:00

Authors: Satoshi Takeya, Akio Yoneyama, Kazuhiro Ueda, Kazuyuki Hyodo, Hiroshi Yamawaki, Hiroshi Fujihisa, Yoshito Gotoh, and Tohoru Takeda
To develop a novel observation system for water accumulation and freezing in gas diffusion layers (GDLs) of polymer electrolyte fuel cells (PEFCs), phase-contrast X-ray imaging using the diffraction-enhanced imaging (DEI) technique was performed at temperatures between 233 and 293 K. The use of high-energy X-rays of 35 keV in the DEI technique enabled the visualization of ice and meltwater in carbon paper sandwiched by two Al plates of 0.50 mm thickness. It was proven that the DEI technique using a temperature-controlled chamber enables in situ observation of ice and water in GDLs under different temperature conditions, which is critical for achieving high performance PEFCs.

Temporal Characteristics of Pulsed Squeezing in a Nonlinear Optical Waveguide

2013-03-08T09:00:00+09:00

Authors: Yujiro Eto, Akane Koshio, Akito Ohshiro, Yun Zhang, Masahide Sasaki, and Takuya Hirano
We experimentally investigate the temporal characteristics of picosecond squeezed pulses generated via an optical parametric amplification in a periodically poled MgO:LiNbO_{3} waveguide. The noise variances for the various time delays between the squeezed pulse and a local oscillator are measured using a balanced homodyne detector. The measured delay dependence is asymmetric, and this asymmetry indicates that the phase chirping of the squeezed pulse is different from that of the local oscillator pulse. We show that the observed squeezing can be improved by using the pulse shaping of the local oscillator.

Technology Evolution for Silicon Nanoelectronics: Postscaling Technology

Shigeaki Zaima — 2013-03-05T09:00:00+09:00

Authors: Shigeaki Zaima
Si ultralarge-scale integration (ULSI) circuits have been developed by downscaling device dimensions on the basis of the concept of scaling, following Moore's law. However, continued downscaling in future ULSI devices will become more difficult because of an increase in the number of technological and economic problems. Therefore, it is necessary to establish a new direction of technological development different from that based on downscaling. In this review, a technology that realizes devices with high performance, integration, and functionality independently of downscaling, is referred to as a postscaling technology, and the current status and future perspectives of postscaling technology are briefly summarized and discussed.

Temperature-Dependent Sellmeier Equation for Refractive Index of 1.0 mol % Mg-Doped Stoichiometric Lithium Tantalate

Hwan Hong Lim, Sunao Kurimura, Toshio Katagai, and Ichiro Shoji — 2013-03-04T09:00:00+09:00

Authors: Hwan Hong Lim, Sunao Kurimura, Toshio Katagai, and Ichiro Shoji
Mg-doped stoichiometric lithium tantalate (SLT) is a promising material in high power generation, due to its high thermal conductivity. The accuracy of the temperature-dependent Sellmeier equation for Mg-doped SLT is important for designing high-power-frequency converters. We propose a temperature-dependent Sellmeier equation for the extraordinary refractive index of 1.0 mol % Mg-doped SLT. The equation is fitted with measured data in the first-order quasi-phase-matched (QPM) second harmonic generation (SHG) and optical parametric oscillation (OPO) with the fundamental and pump wavelengths being both 1.064 µm and previously published data [Jpn. J. Appl. Phys. 41 (2002) 465] of SLT. The equation allows us to predict accurate QPM periods in the range of 0.5–4 µm wavelength and in temperature range of 30–170 °C.

Local Resonance Broadband Gap in a Homogeneous Plate with Periodic Truncated Cones

Jiu-jiu Chen, Hong-bo Zhang, and Xu Han — 2013-03-04T09:00:00+09:00

Authors: Jiu-jiu Chen, Hong-bo Zhang, and Xu Han
We investigate the band structures in a homogeneous plate with periodic truncated cones for the square lattice based on finite element method (FEM). The radius of the truncated cone is gradually reduced from the lower base to the upper base. Compared to the classical stubbed phononic plates, a considerable enlargement of the bandwidth by a factor of 2.04 is obtained by varying the semiangle of the truncated cone, while the truncated cone's weight is only 65.19% of that of the cylinder of the stubbed case. Moreover the relative bandwidth is also enlarged by a factor of 1.68. We show that this band gap enlargement is due to the acoustic waves of different wavelengths is localized at the different parts of the truncated cone. These characteristics of elastic or acoustic waves suggest potential applications in aerospace.

Structure Parameters and Electric Field Effects on Exciton Binding Energies of CdTe/ZnTe Quantum Rings

Woo-Pyo Hong, Seoung-Hwan Park, and Young-Dae Jung — 2013-03-04T09:00:00+09:00

Authors: Woo-Pyo Hong, Seoung-Hwan Park, and Young-Dae Jung
We study the effects of the structural parameters such as the wetting layer thickness and the size of self-assembled CdTe/ZnTe quantum rings (QRs) under an external electric field on the exciton binding energies due to Coulomb interaction between electrons and holes with a finite-element method based on the linear elasticity theory of solids and the eight-band k·p Hamiltonian. The exciton binding energies are shown to decrease linearly with increasing the outer diameter of QRs and to decrease with increasing the wetting layer thickness, agreeing with the results of the truncated quantum dots (QDs). It is shown that the isotropic probability density distribution of the electron and the hole waves is strongly affected by the static electric field and shifts in opposite directions with increasing electric field intensity, i.e., by the quantum Stark effect, similar to the case of truncated QDs. However, it is demonstrated that both the exciton binding energies with different QR heights decrease linearly but saturate to a constant value, compared to those of truncated QDs which decrease parabolically with increasing electric field intensity.

Inactivation of Escherichia coli Using the Atmospheric Pressure Plasma Jet of Ar gas

Takeshi Homma, Masakazu Furuta, and Yuichiro Takemura — 2013-03-04T09:00:00+09:00

Authors: Takeshi Homma, Masakazu Furuta, and Yuichiro Takemura
Germicidal treatments of Escherichia coli on Langmuir–Blodget (LB) agar were performed using the atmospheric pressure plasma jet sources of Ar gas in the ambient air. Shorter distances from the nozzle of the plasma jet device were more effective in achieving higher bactericidal effects on E. coli grown on LB agar. The surface temperature of the agar was monitored and the spectroscopic analysis of the plasma jet was performed in order to evaluate the factors contributing to the bactericidal effect, such as heating, UV emission, and radical formation caused by the plasma jet. Although the plasma jet raised the surface temperature of LB agar up to about 40 °C, the bactericidal effect was not observed. Moreover, the bactericidal effect of UV (200–300 nm) emitted from the plasma jet was negligible compared with the effects of ions and radical species generated by the atmospheric plasma. The results suggest that the ions and radical species generated by the atmospheric pressure plasma jet are critical for high bactericidal effects on E. coli.

Influence of Light Intensification by Subsurface Cracks on KH_{2}PO_{4} Crystal's Laser Induced Damage Threshold

2013-03-01T09:00:00+09:00

Authors: Mingjun Chen, Mingquan Li, Chenhui An, Lian Zhou, Jian Cheng, Yong Xiao, and Wei Jiang
The subsurface damage introduced by single point diamond turning (SPDT) is an important precursor that decrease the laser induced damage threshold (LIDT) of KH_{2}PO_{4} (KDP) crystal. In this paper, based on the Fourier model theory, the modulation property of subsurface crack is analyzed. Research results indicate that light intensification by subsurface crack is an important mechanism of KDP failure. When the feed speed increases under the certain cutting depth, the subsurface damage depth and LIDT have the inverse changing trend. Namely that the intention of obtaining smaller damage depth by choosing suitable cutting parameters, will be also beneficial to improve the surface LIDT of KDP crystal. The combination of feed and cutting depth decides the damage depth together under the given spindle speed and tool geometry. The small feed is beneficial for improving the LIDT when cutting depth is large, while the situation is opposite when cutting depth is small.

Moisture Barrier Properties of Al_{2}O_{3} Films deposited by Remote Plasma Atomic Layer Deposition at Low Temperatures

2013-03-01T09:00:00+09:00

Authors: Hagyoung Choi, Sanghun Lee, Hyunsoo Jung, Seokyoon Shin, Giyul Ham, Hyungtak Seo, and Hyeongtag Jeon
We report the effect of process temperature on moisture permeation barrier properties of Al_{2}O_{3} films deposited by remote plasma atomic layer deposition (RPALD) at various low temperatures from 50 to 200 °C. XPS analysis of O 1s peak reveals that the O–H ratio decreases with process temperature from 38.1% at 50 °C to 25.8% at 200 °C. The water transmission rates using electrical Ca degradation test indicates that the 100 nm Al_{2}O_{3} film enhances the moisture barrier performance from 2.0×10^{-2} to 5.0×10^{-4} g m^{-2} day^{-1} with increasing the process temperature. This result indicates that increasing the process temperature improves the moisture permeation barrier properties significantly even in RPALD process. It is attributed to the increase in the Al_{2}O_{3} mass density due to the decrease of relatively O–H ratio with increase in temperature as revealed by XPS O 1s peak deconvolution and FTIR analysis in the Al_{2}O_{3} films.

Relative Electron Impact Ionization Probabilities of O, O_{2}, and Ar Components in Laser-Detonation Hyperthermal Beams

Kumiko Yokota, Shigeru Yasuda, Akira Mizutani, and Masahito Tagawa — 2013-03-01T09:00:00+09:00

Authors: Kumiko Yokota, Shigeru Yasuda, Akira Mizutani, and Masahito Tagawa
The relative ionization probabilities of laser-detonation hyperthermal O, O_{2}, and Ar components in Ar+O_{2} mixed molecular beams were evaluated for investigation of the effect of the space environment. In a high-energy beam, the complete decomposition of O_{2} was observed from the time-of-flight (TOF) spectra, which was due to high-energy collisions between O_{2} and Ar. Relative ionization probabilities of O and O_{2} of 0.27 and 0.79, respectively, with respect to Ar were evaluated by assuming the complete decomposition of O_{2} in the beam. These values can be applied in studies on the effect of the space environment in the sub-low Earth orbit region where simultaneous hyperthermal N_{2} and O bombardment should be simulated.

A Fabry–Pérot Etalon with an Ultralow Expansion Ceramic Spacer

2013-02-28T09:00:00+09:00

Authors: Kazumoto Hosaka, Hajime Inaba, Daisuke Akamatsu, Masami Yasuda, Jun Sugawara, Atsushi Onae, and Feng-Lei Hong
We have developed a Fabry–Pérot etalon with an ultralow expansion ceramic spacer and investigated the thermal properties of the ceramic. We found that the ceramic cavity has a “zero crossing temperature” at room temperature where the thermal expansion coefficient crosses zero. The sensitivity of the thermal expansion coefficient of the ceramic to temperature change is about five times greater than that of ultralow expansion (ULE) glass at around the zero cross temperature. Nevertheless, owing to the high specific rigidity and relatively low thermal expansion at room temperature, the ceramic should be an attractive material for long optical cavities that can reduce the effect of the thermal noise relatively.

Effects of Tilt Angle, DNA Concentration, and Surface Potential on Directed Alignment of DNA Molecule for the Application to Nanodevices

Hyung Jin Kim and Byungyou Hong — 2013-02-28T09:00:00+09:00

Authors: Hyung Jin Kim and Byungyou Hong
This paper reports an efficient approach to control both the density and direction of highly aligned DNA molecules and thus DNA-templated gold nanowires (AuNWs) on Si chips. We utilized tilting method to prepare stretched DNA structures on SiO_{2}/Si substrate and found important parameters in the alignment process that tilt angle, DNA concentration, and surface potential are controlled the density and structure of DNA aligned on the surface. In additional, we also can be directly connected DNA-templated AuNWs between two terminal electrodes on Si chips. This method also describes a simple way to form singled, bundled and networked DNA arrays on Si substrates.

Bias-Assisted Photochemical Planarization of GaN(0001) Substrate with Damage Layer

2013-02-28T09:00:00+09:00

Authors: Shun Sadakuni, Junji Murata, Yasuhisa Sano, Keita Yagi, Satoshi Matsuyama, and Kazuto Yamauchi
An electrochemical polishing process for an n-GaN(0001) surface with a subsurface damage layer has been developed that involves irradiating with ultraviolet (UV) light and applying a voltage. In this method, a positively biased GaN substrate is exposed to UV light to oxidize its surface. The oxide layer does not dissolve in solution; rather it is chemically removed from the protruding region by a solid acid catalyst, which functions as a polishing pad. The wafer was prepared by mechanical polishing with diamond particles. Without a bias, the removal rate is quite low because photoinduced carriers are rapidly depleted through recombination at crystallographic defects. In contrast, when a bias is applied, photoinduced electrons and holes are forcibly separated so that they contribute to surface oxidation. Consequently, the damaged surface was effectively planarized when a bias was applied.

Electron Optical Properties of Microcolumn with Field Emitter

2013-02-28T09:00:00+09:00

Authors: Yoichiro Neo, Akifumi Koike, Takahiro Fujino, Hidenori Mimura, Hidekazu Murata, Tomoya Yoshida, Takashi Nishi, and Masayoshi Nagao
We present the electron optical properties of a newly designed microcolumn. The microcolumn consists of an objective lens and an electron gun, which is composed of a microscale field emitter and a condenser lens. An acceleration lens was used as the objective lens. Each component was optimized to maximize its own function while minimizing its impact on the functions of the other components. The current–voltage characteristics of each electrode were evaluated. The current variation characteristics of each electrode indicated that each optimized structure could be used to control the electron beam. The objective lens could also focus the electron beam to a diameter of approximately 40 µm at a working distance of 2 mm and 400× magnification when no acceleration electric field was applied between the microcolumn and the anode.

Preparation of Naturally Textured Aluminum-Doped Zinc Oxide Films on Flexible Poly(ether sulfone) Substrate by Radio Frequency Magnetron Sputtering

Jae Seok An, Jin Koog Shin, Jong Ho Lee, and Bum Ho Choi — 2013-02-27T09:00:00+09:00

Authors: Jae Seok An, Jin Koog Shin, Jong Ho Lee, and Bum Ho Choi
Transparent conducting oxide (TCO) layers of naturally textured aluminum-doped zinc oxide (AZO) were prepared on flexible poly(ether sulfone) (PES) substrates by controlling the radio frequency (RF) magnetron sputtering power without chemical wet etching, and their morphological, optical, and electrical properties were characterized. Layers with crater structures were formed at a single RF power; whereas at high RF power (2000 W), their surfaces resembled that of chemically wet-etched AZO. Layers were also formed by dual RF sputtering powers: sputtering a 0.15-µm-thick layer at high power and a subsequent 0.45-µm-thick layer at low power produced flakes with larger grains or crater-like structures. The measured visible transmittance of all the layers was >85% – sufficient for use in amorphous silicon (a-Si) thin-film solar cells. The measured optical and electrical properties of the naturally textured AZO layers are comparable to those of chemically wet-etched AZO layers, suggesting a possible method for fabricating inexpensive flexible a-Si thin-film solar cells in fewer steps.

Thermoelectric Properties of Li-Doped CuO

Naoki Yoshida, Tomoyuki Naito, and Hiroyuki Fujishiro — 2013-02-27T09:00:00+09:00

Authors: Naoki Yoshida, Tomoyuki Naito, and Hiroyuki Fujishiro
Thermoelectric properties of CuO doped with alkali metal ions (Li^{+}, Na^{+}, K^{+}) were investigated at temperatures up to 1273 K. Among the doped alkali metal ions, Li^{+} ion was the most effective to enhance the thermoelectric properties. The maximum dimensionless thermoelectric figure of merit ZT and power factor P were, respectively, 3.2×10^{-2} and 1.6×10^{-4} W K^{-2} m^{-1} at 1246 K for the 3.0%-Li-doped CuO. The enhancement of the thermoelectric properties of the CuO system was discussed.

Void and Nanostructure Formations during Thermal Decomposition of 20-nm-Thick Silicon Oxide Layer on Si(100)

Yoshiharu Enta, Kano Ogawa, and Takayuki Nagai — 2013-02-27T09:00:00+09:00

Authors: Yoshiharu Enta, Kano Ogawa, and Takayuki Nagai
We investigate the thermal decomposition of 20-nm-thick silicon oxide layers on Si(100) at a temperature of 1050 °C in vacuum by X-ray photoelectron spectroscopy, scanning Auger electron microscopy, and atomic force microscopy. Time evolutions of chemical-shift components in Si 2p core-level spectra are analyzed with the SiO_{2}-decomposition model based on void formation. The experimental data can be reproduced well if the void area is proportional to the square of the annealing time, being consistent with the model in which the reaction at the void periphery is the rate-limiting step for void growth. Microscopic images show that the void periphery is square with rounded corners, and many silicon nanostructures are formed inside the void. These observations reflect reaction processes of the thermal decomposition of the silicon oxide layer.

High Birefringence of the YVO_{4} Crystal in the Terahertz Frequency Range

Tsong-Ru Tsai, Jia-Hao Wang, and Hai-Pang Chiang — 2013-02-27T09:00:00+09:00

Authors: Tsong-Ru Tsai, Jia-Hao Wang, and Hai-Pang Chiang
The optical constants of YVO_{4} crystal in the frequency range of 0.2 to 1.0 THz were determined using terahertz time-domain spectroscopy. The extraordinary-ray refractive indices varied from 4.05 to 4.07 and the ordinary-ray refractive indices were approximately 3.07. We found that YVO_{4} crystal had a large and nearly constant birefringence of ∼0.985. In addition, the power absorptions for YVO_{4} were less than 7 cm^{-1}. Our results indicated that YVO_{4} crystal has a potential for applications in the THz frequency range.

Narrow Diameter Distribution of Horizontally Aligned Single-Walled Carbon Nanotubes Grown Using Size-Controlled Gold Nanoparticles

Kazuki Yamada, Hiroki Kato, and Yoshikazu Homma — 2013-02-26T09:00:00+09:00

Authors: Kazuki Yamada, Hiroki Kato, and Yoshikazu Homma
Diameter control of horizontally aligned single-walled carbon nanotubes (SWCNTs) is highly desired for controlling electronic properties and applying SWCNTs to devices. Preparation of size-ordered catalyst nanoparticles is one of the approaches to synthesizing diameter-controlled SWCNTs. We report the narrow size distribution of gold catalyst nanoparticles obtained by thermal annealing. The size of gold nanoparticles on an ST-cut quartz substrate changed dramatically when nanoparticles were annealed in Ar/H_{2} atmosphere. Almost all the gold nanoparticles diminished in size to less than 2 nm. More than half of them were under 1 nm. The diameters of SWCNTs synthesized from those nanoparticles were narrowly distributed. The average size of SWCNTs was 0.94±0.07 nm. The size correlation between nanoparticles and SWCNTs smaller than 1 nm suggests the possibility of simultaneous control of orientation and diameter of SWCNTs.

Rashba Effect on the Structure of the Bi One-Bilayer Film: Fully Relativistic First-Principles Calculation

Hiroki Kotaka, Fumiyuki Ishii, and Mineo Saito — 2013-02-26T09:00:00+09:00

Authors: Hiroki Kotaka, Fumiyuki Ishii, and Mineo Saito
Using first-principles calculations, we study the spin–orbit interactions and spin textures of a Bi one-bilayer film, which attracts scientific interest because of the topological insulator and so on. The substrate effect is successfully mimicked by applying on electric field in the perpendicular direction of the film, which breaks the inversion symmetry. We study the highest occupied band around the Γ point. Although the vortex of the in-plane spin component is well explained on the basis of the conventional Rashba effect, we find a substantial out-of-plane component which cannot be explained by the conventional Rashba model. This spin texture is similar to that of a multi-bilayer Bi film, which has recently been observed using a spin-resolved angle-resolved photoemission spectroscopy experiment. We also find a spin vortex around the K point although this point has no time-reversal symmetry. We expect that a similar vortex appears in materials having the p3m1 symmetry, whose spin–orbit interactions have recently attracted scientific interest.

Investigation of Positive and Negative Bias Temperature Instability of High-κ Dielectric Metal Gate Metal–Oxide–Semiconductor-Field-Effect-Transistors by Random Telegraph Signal

Da-Cheng Huang, Jeng Gong, and Chih-Fang Huang — 2013-02-26T09:00:00+09:00

Authors: Da-Cheng Huang, Jeng Gong, and Chih-Fang Huang
We investigate the impact of positive and negative bias temperature instability (P/NBTI) on the current degradation by using the drain current random telegraph signal (I_{dRTS}) in high-κ gate dielectric and metal-gate MOSFETs. The samples were stressed at typical BTI oxide electric field (∼7 MV/cm) and I_{dRTS} amplitude (ΔI_{dRTS}) distributions were measured before and after P/NBTI stress. It is shown that I_{dRTS} degradation (ΔI_{dRTS}/I_{dRTS}) in NBTI devices exhibits a wider amplitude distribution than the PBTI one. In addition, we trace trapped charge-induced saturation current I_{Dsat} degradation in P/NBTI stress. As a result, the statistical analysis indicates that ΔI_{Dsat}/I_{Dsat} of the p-MOSFET is larger than ΔI_{Dsat}/I_{Dsat} of the n-MOSFET. Moreover, the lifetime of the device is numerically estimated based on current degradation with or without RTS. We consequently found that P/NBTI lifetime comes worse by considering the effect of RTS.

Direct Evaluation of the Figure of Merit of Thermoelectric Devices by Guarded Hot Plate Method

Su Yong Kwon, Yong-Gyoo Kim, Sanghyun Lee, and Jong Chul Kim — 2013-02-26T09:00:00+09:00

Authors: Su Yong Kwon, Yong-Gyoo Kim, Sanghyun Lee, and Jong Chul Kim
An apparatus for the evaluation of the figure of merit (ZT) of thermoelectric devices has been developed and ZT values have been estimated for a thermoelectric device. The most challenging problem in ZT value evaluation in this apparatus was measuring the thermal conductivity of the devices precisely. We have solved the problem by introducing a primary thermal conductivity measurement technique, a guarded hot plate method, which makes it possible to obtain directly and simultaneously four physical parameters related to the ZT, namely the thermal conductivity, electrical conductivity, Seebeck coefficient, and absolute temperature. The ZT evaluation was performed by a single scan of the temperature difference between the top and bottom surfaces of the device. We also addressed the thermoelectric properties and the power generation efficiency of a commercial thermoelectric device. The evaluation uncertainty of the ZT value was assessed to secure reliability of the apparatus and was found to be 3.59%.

Experimental Demonstration and Numerical Analysis of Microampere Gray Zone Width with Enhanced Operating Margin in Shunted Quasi-One Junction Superconducting Quantum Interference Device Comparators

2013-02-25T09:00:00+09:00

Authors: Shigeyuki Miyajima, Thomas Ortlepp, Hannes Toepfer, Ali Bozbey, and Akira Fujimaki
We evaluated the relationship between the gray zone width and the operating margin for comparators composed of quasi-one-junction superconducting quantum interference devices (QOSs) with shunt resistors, which are often used as high-speed readout circuits in multiple superconductor detector systems. The gray zone width is a good measure of current sensitivity of a single-bit comparator. We numerically analyzed the gray zone width of a QOS comparator and determined the circuit parameters. The gray zone width obtained from the experiments concurred with the results of the numerical analysis and was 2–3 µA at 4.2 K in a QOS comparator composed of three Nb/AlO_{x}/Nb junctions with critical currents of less than 90 µA. The experimentally obtained operating margin for the bias current provided to the comparator was ±15% at the bias current of around 140 µA. These results show that QOS comparators are promising for readout circuits operating up to tens of GHz and imply that gray zone width is the thermal noise in the resistors at 4.2 K.

Conduction-Type Control of Carbon Nanotube Field-Effect Transistors by Ti and Pd Overlayer

Satoshi Ishii, Masato Tamaoki, Shigeru Kishimoto, and Takashi Mizutani — 2013-02-25T09:00:00+09:00

Authors: Satoshi Ishii, Masato Tamaoki, Shigeru Kishimoto, and Takashi Mizutani
The conduction-type of carbon nanotube field-effect transistors (CNTFETs) was controlled by depositing metal overlayers with different work functions (Ti and Pd) onto the side surfaces of the CNT channel of the ambipolar CNTFETs. The devices with the Ti overlayer showed n-type conduction. On the other hand, the devices with the Pd overlayer showed p-type conduction. The phenomena were explained by the suppression of carrier injection from the drain contact by the energy barrier formed at the CNT-overlayer source-side contact.

Analysis of Truncation Error for Dual-Mixer Time-Difference Measurement System Using Discrete Fourier Transformation

Shinya Yanagimachi, Ken Hagimoto, and Takeshi Ikegami — 2013-02-25T09:00:00+09:00

Authors: Shinya Yanagimachi, Ken Hagimoto, and Takeshi Ikegami
For the dual-mixer time-difference method using the discrete Fourier transformation, the formulation of the truncation error to determine the time difference between two oscillators is derived. It is found that serious error occurs due to the truncation error with a larger frequency difference between two oscillators. The condition of the discrete Fourier transformation to determine the frequency difference between two oscillators with sufficiently high accuracy for atomic clocks is obtained.

Photon Counting Histogram Using Numerical Data of Point Spread Function

Naofumi Terada, Tamotsu Zako, and Mizuo Maeda — 2013-02-25T09:00:00+09:00

Authors: Naofumi Terada, Tamotsu Zako, and Mizuo Maeda
Photon counting histogram (PCH) is a fluorescence fluctuation method that can quantify the brightness and concentration of different fluorescent molecules in solution at a single molecule level using confocal optics. The current method assumes that the point spread function (PSF) of confocal optics is Gaussian function. However, this could be problematic when the actual PSF profile is not Gaussian. Here, we propose an improved PCH analysis method using numerical PSF data. This method does not require any analytical equation for the PSF profile, and can handle any arbitrary shape of PSF. We report a proof-of-concept estimation of this method using a model PSF.

Chemical Structure of Interfacial Transition Layer Formed on Si(100) and Its Dependence on Oxidation Temperature, Annealing in Forming Gas, and Difference in Oxidizing Species

2013-02-22T09:00:00+09:00

Authors: Tomoyuki Suwa, Akinobu Teramoto, Yuki Kumagai, Kenichi Abe, Xiang Li, Yukihisa Nakao, Masashi Yamamoto, Hiroshi Nohira, Takayuki Muro, Toyohiko Kinoshita, Shigetoshi Sugawa, Tadahiro Ohmi, and Takeo Hattori
The angle-resolved Si 2p photoelectron spectra arising from a interfacial transition layer formed on a Si(100) were measured with a probing depth of nearly 2 nm. The novel analytical procedure of these spectra was developed by considering that one SiO_{2} monolayer, two compositional transition layers (CTLs), and one Si monolayer constituting the Si substrate surface are continuously connected with each other to maintain the areal density of Si atoms. It was found for thermally grown transition layers that two CTLs are formed on the oxide side of the CTL/Si interface and the chemical structures correlated with the residual stress appear on the Si substrate side of the interface. The effects of oxidation temperature in the range from 900 to 1050 °C, annealing in the forming gas, and oxidation using oxygen radicals on the chemical structures of transition layers formed on both sides of the interface were also clarified.

Flat Band Slow Light Performance in Dual-Slot Silicon-on-Insulator Based Photonic Crystal Waveguide

Huiping Tian, Jian Zhou, Yi Zhai, and Yuefeng Ji — 2013-02-22T09:00:00+09:00

Authors: Huiping Tian, Jian Zhou, Yi Zhai, and Yuefeng Ji
The photonic band structure and slow light performance in dual-slot photonic crystal waveguide based on silicon-on-insulator (SOI) substrate are studied by using three-dimensional (3D) plane wave expansion method. The numerical results show that both the position and the width of the slots have significant effect on photonic band structure. The guided mode edge and the photonic band gap increases with the increasing of the two slots' widths. When slots move close to the boundary of the waveguide, a flat band of slow light appears. The slow light property has also been discussed by modifying the radius of the two rows of air holes nearest to the dual-slot waveguide. The negligible dispersion bandwidths ranging from 6.70 to 25.70 nm for group indices from 62 to 20 are obtained, respectively. The numerical results show that the proposal structure has potential application in optical buffer.

High-Performance 2,8-Difluoro-5,11-bis(triethylsilylethynyl) Anthradithiophene Thin-Film Transistors Facilitated by Predeposited Ink-Jet Blending

Jeong In Han, Chang-Yoon Lim, Sung Kyu Park, and Yong-Hoon Kim — 2013-02-21T09:00:00+09:00

Authors: Jeong In Han, Chang-Yoon Lim, Sung Kyu Park, and Yong-Hoon Kim
We report high-performance ink-jet-printed 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TESADT) organic thin-film transistors (OTFTs) facilitated by polymer blending. The film morphology and crystal structure of diF-TESADT films were greatly improved by printing on a predeposited poly(α-methyl styrene) (PαMS) layer possibly due to the confined droplet area and thus increased intermolecular interactions. Additionally, partial dewetting and the formation of irregular film shapes were effectively controlled resulting in uniform and improved device performance in the predeposited blending system. Through a proper optimization of printing parameters such as substrate temperature and processing solvent, diF-TESADT TFTs with an average field-effect mobility of 0.34±0.13 cm^{2} V^{-1} s^{-1} (max 0.64 cm^{2} V^{-1} s^{-1}) and subthreshold slope of 0.456±0.090 V decade^{-1} have been achieved.

Low-Dose-Rate Computed Tomography System Utilizing 25 mm/s-Scan Silicon X-ray Diode and Its Application to Iodine K-Edge Imaging Using Filtered Bremsstrahlung Photons

2013-02-21T09:00:00+09:00

Authors: Ryo Matsushita, Eiichi Sato, Yutaka Yanbe, Hiraku Chiba, Tomoko Maeda, Osahiko Hagiwara, Hiroshi Matsukiyo, Akihiro Osawa, Toshiyuki Enomoto, Manabu Watanabe, Shinya Kusachi, Shigehiro Sato, Akira Ogawa, and Jun Onagawa
A low-dose-rate X-ray computed tomography (CT) system is useful for reducing absorbed dose for patients. The CT system with a tube current of sub-mA was developed using a silicon X-ray diode (Si-XD). The Si-XD is a high-sensitivity Si photodiode (PD) selected for detecting X-ray photons, and the X-ray sensitivity of the Si-XD was twice as high as that of Si-PD cerium-doped yttrium aluminum perovskite [YAP(Ce)]. X-ray photons are directly detected using the Si-XD without a scintillator, and the photocurrent from the diode is amplified using current–voltage and voltage–voltage amplifiers. The output voltage is converted into logical pulses using a voltage–frequency converter with a maximum frequency of 500 kHz, and the frequency is proportional to the voltage. The pulses from the converter are sent to the differentiator with a time constant of 500 ns to generate short positive pulses for counting, and the pulses are counted using a counter card. Tomography is accomplished by repeated linear scans and rotations of an object, and projection curves of the object are obtained by the linear scan. The exposure time for obtaining a tomogram was 5 min at a scan step of 0.5 mm and a rotation step of 3.0°. The tube current and voltage were 0.55 mA and 60 kV, respectively, and iodine K-edge CT was carried out using filtered bremsstrahlung X-ray spectra with a peak energy of 38 keV.

Structural Change in Smectic Liquid Crystal Nanofilm under Molecular-Scale Confinement Measured by Synchrotron X-ray Diffraction

2013-02-21T09:00:00+09:00

Authors: Shinya Nakano, Masashi Mizukami, Noboru Ohta, Naoto Yagi, Ichiro Hatta, and Kazue Kurihara
The determination of liquid structures under nanometer-scale confinement is important in advanced sciences and technologies. Synchrotron X-ray diffraction measurement was performed to investigate the structure of a smectic liquid crystal, 4-cyano-4'-octylbiphenyl (8CB), nanofilm (thickness: 1.7 ±0.5 nm) confined between mica surfaces. A diffraction peak at q = 1.99 nm^{-1}, corresponding to the lamellar spacing of 8CB, appeared immediately after 8CB was injected between the surfaces. This diffraction peak gradually decreased with time, indicating the structural change in 8CB from the ordered to the disordered state. The relaxation time was ca. 60 min and the diffraction peak almost disappeared at 100 min after 8CB injection. We could directly monitor the time course of the structural change in the smectic liquid crystal under molecular-scale confinement.

Analysis of P-Doped Polycrystalline Silicon Missing of W-Polycide Gate for 2X nm NAND Flash

Chun-Chi Chen, Wen-Chung Yang, Te-Yuan Yin, Hung-Ju Chien, and Tzung-Hua Ying — 2013-02-21T09:00:00+09:00

Authors: Chun-Chi Chen, Wen-Chung Yang, Te-Yuan Yin, Hung-Ju Chien, and Tzung-Hua Ying
We studied the control-gate (CG-Poly) missing behavior after post in-situ steam generation (ISSG) re-oxidation for W-polycide gate of 2X nm NAND Flash and attempted to determine the possible mechanism. On the other hand, various effective countermeasures were also been proposed. We found that Si atoms diffuse upward on WSi_{2.3} films, driven out of the underlying doped polycrystalline silicon film during steam radical oxidation process based on energy dispersive X-ray (EDX) analysis. A 2.5 nm remaining of SiN at least on sidewall before oxidation results in CG-Poly missing free and WSi_{x} deformation improvement simultaneously. A selective oxidation such as water vapor generator (WVG) and rapid thermal oxidation (RTO) can achieve the same efficient performance. Additionally, less intrinsic tensile stress of WSi_{x} film employment also shows immunity against CG-Poly missing. Satisfactory sidewall barrier utilization for ISSG oxidation, diverse thermal oxidation selection, and even by WSi_{x} film property modifying might avoid poly-Si missing occurrence and reduce the WSi_{x} film deformation extent for the narrower dimension of 2X nm and beyond.

Low Contact Resistance P-Type Electrode for Nonpolar m-Plane GaN

Mitsuaki Oya and Toshiya Yokogawa — 2013-02-19T09:00:00+09:00

Authors: Mitsuaki Oya and Toshiya Yokogawa
A low contact resistance p-type electrode for nonpolar m-plane GaN was obtained using Mg as the electrode material. Ga atoms diffused toward the Mg electrode after heat treatment. Because the Ga vacancies act as acceptors and form levels in the Schottky barrier, we consider hopping conduction through the Ga vacancy levels to be the main mechanism for the formation of the p-type ohmic contact to m-plane GaN. The specific contact resistance was reduced to 8×10^{-4} Ω cm^{2} by optimizing the heat treatment temperature and the Mg thickness. A significant reduction in the operating voltage of m-plane GaN LEDs was achieved by using this electrode technology.

Characteristics of Ohmic Contacts to n-Type Boron Phosphide

2013-02-18T09:00:00+09:00

Authors: Yuji Ino, Suzuka Nishimura, Muneyuki Hirai, Satoru Matsumoto, and Kazutaka Terashima
We grew n-type boron phosphide (BP) (100) on a p-type Si(100) substrate by hydride vapor phase epitaxy. Electrical contacts are important for electrical evaluations and device applications, but the resistivity of ohmic contacts to BP has been little studied. We evaluated the contact characteristics for Al, Au, In, Ti, and Pt by annealing at temperatures in the range 300–500 °C for annealing times up to 50 min using a circular transmission line model pattern. Ohmic characteristics were obtained for the Al, Au, In, and Ti contacts. For the ohmic samples, we calculated the specific contact resistance ρ_{c} and observed a metal–BP interface by cross-sectional transmission electron microscopy. The minimum specific contact resistance ρ_{c} was 2×10^{-5} Ω cm^{2} for the Au/In/n-BP sample annealed at 500 °C for 50 min. For the present samples, thermionic-field emission is considered to be the dominant carrier transport process across the metal–BP interface.

Graphene Manipulation on 4H-SiC(0001) Using Scanning Tunneling Microscopy

2013-02-18T09:00:00+09:00

Authors: Peng Xu, Matthew L. Ackerman, Steven D. Barber, James K. Schoelz, Dejun Qi, Paul M. Thibado, Virginia D. Wheeler, Luke O. Nyakiti, and Rachael L. Myers-Ward
Atomic-scale topography of epitaxial multilayer graphene grown on 4H-SiC(0001) was investigated using scanning tunneling microscopy (STM). Bunched nano-ridges ten times smaller than previously recorded were observed throughout the surface, the morphology of which was systematically altered using a relatively new technique called electrostatic-manipulation scanning tunneling microscopy. Transformed graphene formations sometimes spontaneously returned to their original morphology, while others permanently changed. Using an electrostatic model, we calculate that a force up to ∼5 nN was exerted by the STM tip, and an energy of around 10 eV was required to alter the geometry of a ∼100×200 nm^{2} area.

Study of Growth Enhancement of Multiwalled Carbon Nanotubes by Chlorine-Assisted Chemical Vapor Deposition

2013-02-18T09:00:00+09:00

Authors: Crina Ghemes, Adrian Ghemes, Morihiro Okada, Hidenori Mimura, Takayuki Nakano, and Yoku Inoue
In this paper, we investigate the effect of chlorine as a growth promoter in the synthesis of multiwalled carbon nanotubes (MWCNTs). We find that the addition of chlorine gas to the chemical vapor deposition process reduces the amount of amorphous carbon deposited on the MWCNT surfaces and results in a longer catalyst lifetime. By using optimum growth parameters, the catalyst remains active for 75 min. Moreover, the growth rate is also relatively high resulting in the maximum CNT array height of 3.5 mm. The MWCNT arrays grown with and without chlorine are compared.

Hard X-ray Microprobe and Scanning Microscopy with Spherical-Aberration-Corrected Grazing-Incident Spherical-Concave Mirror Optics

Yoshio Suzuki and Akihisa Takeuchi — 2013-02-18T09:00:00+09:00

Authors: Yoshio Suzuki and Akihisa Takeuchi
Total-reflection mirror optics with four spherical-concave mirrors has been developed for hard X-ray microfocusing. The optical system consists of a pair of tandem spherical-concave mirrors. Each tandem-mirror system is assembled to eliminate spherical aberration of gazing-incident optics with spherical mirrors, and the two tandem-mirror systems are combined in a crossed-mirror geometry in order to achieve two-dimensional focusing. Characterization of the quad-mirror system as an X-ray focusing device was performed at beamline 20XU of SPring-8. The focused beam size at an X-ray energy of 10 keV was measured to be 170×190 nm^{2} in full-width at half-maximum, and the X-ray energy dependence of focusing properties was evaluated in the energy range from 8 to 14 keV. Preliminary experiments on scanning microscopy were also carried out.

Efficiency Enhancement of Indirect Transverse Laser Cooling with Synchro-Betatron Resonant Coupling by Suppression of Beam Intensity

2013-02-15T09:00:00+09:00

Authors: Hikaru Souda, Masao Nakao, Hiromu Tongu, Kouichi Jimbo, Kazuya Osaki, Hiromi Okamoto, Yosuke Yuri, He Zhengqi, Manfred Grieser, and Akira Noda
The efficiency of indirect transverse laser cooling with synchro-betatron resonance coupling has been improved with the reduction in beam intensity by scraping the tail part of the beam. In order to measure the beam size at a low beam intensity, a new scheme to measure the beam profile by observation of the survival ratio with changing the scraper position has been established. With 10^{4} particles, the transverse cooling time was reduced to 1.2 s, and the cooled horizontal and vertical beam sizes were 0.19 and 0.61 mm, corresponding to temperatures of 20 and 29 K, respectively, which is largely improved compared with that in our previous experiment [Nakao et al.: Phys. Rev. ST Accel. Beam 15 (2012) 110102].

Microstructural Observations in (Na_{0.5}K_{0.5})NbO_{3} Ceramics with CuO and ZnO Additives

Young Heon Kim, Hyun Ryu, Yang-Koo Cho, Hwack-Joo Lee, and Sahn Nahm — 2013-02-15T09:00:00+09:00

Authors: Young Heon Kim, Hyun Ryu, Yang-Koo Cho, Hwack-Joo Lee, and Sahn Nahm
The characterizations of CuO and ZnO pockets which had formed in (Na_{0.5}K_{0.5})NbO_{3} (NKN) matrix sintered at 920 °C with CuO of 1.5 mol % and ZnO of 1.5 and 3.0 mol % as the additives were investigated from a microstructural point of view using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). Two types of pockets, composed of CuO and ZnO as a dominant component, were observed in the microstructure as new microstructure constituents. The abnormal grain growth has occurred by the liquid phase sintering. The pockets were melted partially or completely by the interactions with element Na in the matrix which has formed a eutectic compound whose melting point is lower than the sintering temperature. The reaction starts at the interfaces between the pocket and matrix and the kinetics depends not only on the size of the pocket but also on the environments where the pockets are located. When the additive content of ZnO was increased to 3.0 mol %, there are interactions between CuO and ZnO and both elements are found in the compound pocket. The sintering kinetics was much enhanced by the presence of both additives.

Fabrication of 200-nm Dot Pattern on 15-m-Long Polymer Sheet Using Sheet Nanoimprint Method

2013-02-15T09:00:00+09:00

Authors: Masahiko Ogino, Mitsuru Hasegawa, Keiji Sakaue, Shuuichi Nagai, and Akihiro Miyauchi
Nanoimprint technology is one of the more promising methods for nano-fabrication. The thermal nanoimprint method can fabricate various kinds of thermoplastic materials and its process consists of heating, pressing, cooling, and separation and a lot of research was reported. We proposed and developed a sheet nanoimprint system that enables for continuous treatment of these four basic steps by introducing a belt-shaped nano-mold. We tried to fabricate dot patterns on polymer films by using a sheet nanoimprint method in this work. A 200 nm in diameter and 240 nm tall dots (aspect ratio 1.4) were formed directly onto a 15-m-long polystyrene film. It is important in the field of industrial applications to fabricate nano-scale patterns over a large area with a high throughput. We demonstrated that the sheet nanoimprint is an attractive method for the direct patterning of nano-scale patterns on thermo-plastic films.

Fabrication of Parylene-Based High-Aspect-Ratio Suspended Structure Using a Silicon-on-Insulator Wafer

Wen-Cheng Kuo and Chen-Wei Chen — 2013-02-15T09:00:00+09:00

Authors: Wen-Cheng Kuo and Chen-Wei Chen
In this study, we fabricated a parylene-based high-aspect-ratio suspended structure using a definition silicon-on-insulator (SOI) wafer. In this process a silicon micro trench is used as a mold, in which parylene beams are fabricated through the deposition and removal of parylene in multiple stages, after which the structure is released in a hydrofluoric acid solution to remove the buried oxide layer in the SOI wafer, followed by supercritical drying for preventing stiction. Compared with conventional processes, our process exploits the advantages of the SOI wafer to eliminate the extra oxide mask or the support wafer for structure release, thereby reducing process complexity and cost. The reactive-ion etching (RIE) lag effect and notch effect are also considered in this paper. In this study, we fabricated the test devices of the parylene beams without voids inside, which were integrated with a thermal actuator and a comb-drive actuator. Compared with silicon suspended beams, the flexibility of the parylene beams and the uniformity of device thickness are suitable for actuators with large in-plane displacements and low driving forces, and also for sensors with high sensitivity.

Microscopic Thickness Uniformity and Time-Dependent Dielectric Breakdown Lifetime Dispersion of Thermally Grown Ultrathin SiO_{2} Film on Atomically Flat Si Surface

Ryu Hasunuma, Yusuke Hayashi, Masahiro Ota, and Kikuo Yamabe — 2013-02-14T09:00:00+09:00

Authors: Ryu Hasunuma, Yusuke Hayashi, Masahiro Ota, and Kikuo Yamabe
Microroughness at the surface and interface of SiO_{2} thermally grown on an atomically flat Si terrace was investigated by atomic force microscopy. Although surface protuberances on SiO_{2} increased in height during oxidation, their relative locations were preserved. Their positions were mostly determined in the initial stage of oxidation and their heights increased during the subsequent oxidation. It was also found that, at many positions, protuberances on the SiO_{2} surface correspond to dimples at the interface and the dimples on the SiO_{2} surface correspond to the protuberances on the Si/SiO_{2} interface. With decreasing thickness, the thickness of the SiO_{2} layer becomes two-dimensionally less uniform. The Weibull slope of the time-dependent dielectric breakdown lifetime decreased when the thermal SiO_{2} films were grown on rougher Si substrates, which was attributed to film thickness nonuniformity. The SiO_{2} film formed on well-defined Si wafers showed a higher microscopic thickness uniformity and higher long-term reliability.

Lens Coupler and Magnetic Field Terahertz Emission Enhancement in InSb and InAs under 1.55-µm Excitation

2013-02-14T09:00:00+09:00

Authors: Hidekazu Nakajima, Christopher T. Que, Elmer S. Estacio, Kohji Yamamoto, and Masahiko Tani
Terahertz (THz) emission from InSb and InAs utilizing an MgO lens coupler in conjunction with an applied magnetic field is reported. A THz peak amplitude enhancement of 74 times in InSb compared to 26 times in InAs was observed. The considerable enhancement in InSb is attributed to its large Hall angle, small THz divergence and reduced total internal reflection. A corresponding emission shift to lower THz frequencies in both samples was observed due to the spectral dependence of the MgO lens' collection efficiency. This enhancement configuration is easily applicable in the design of a compact THz time-domain spectroscopy system.

Graphene Layer Formation on Polycrystalline Nickel Grown by Chemical Vapor Deposition

Kenichi Kanzaki, Hiroki Hibino, and Toshiki Makimoto — 2013-02-14T09:00:00+09:00

Authors: Kenichi Kanzaki, Hiroki Hibino, and Toshiki Makimoto
We studied the structure of graphene layers grown by chemical vapor deposition on polycrystalline nickel. The conditions of the polycrystalline nickel catalyst (size of fine crystals and surface roughness) were controlled by cyclic heating and cooling, and its effect on the graphene layer formation was evaluated. By increasing the average size of the nickel fine crystals and thereby increasing of the surface roughness, nonuniformity of the graphene sheet numbers tends to increase. A marked change in graphene sheet number tends to occur at discontinuities in the polycrystalline nickel surfaces. From the structural analysis, the graphene layer is found to be made up of single or multiple crystal graphene thin films with different crystallographic directions. The size of each thin film is independent of and not restricted by the size of the nickel fine crystals, and a certain thin film passes over the discontinuities.

Effect of O_{3} and Aqueous Ammonia on Crystallization of MgO Thin Film Grown by Mist Chemical Vapor Deposition

2013-02-14T09:00:00+09:00

Authors: Toshiyuki Kawaharamura, Kazuharu Mori, Hiroyuki Orita, Takahiro Shirahata, Shizuo Fujita, and Takashi Hirao
Mist chemical vapor deposition (CVD) has been applied to fabricate MgO thin films under atmospheric pressure. In this work, to fabricate highly crystalline MgO thin films at low temperature, the effects of ozone gas (O_{3}), aqueous ammonia (NH_{3}), and a combination of O_{3} and NH_{3} on the crystallization temperature were studied by comparing samples grown under a standard condition of inactive gas such as argon (Ar). It was clarified that the crystallization temperature was decreased from 450 to 400 °C by the assistance of O_{3} and the crystallinity was improved by the addition of NH_{3}. The growth of higher crystallinity MgO thin films at temperatures above 400 °C was possible by the combination of O_{3} and NH_{3}, which caused stronger enhancement of the crystallization temperature and crystallinity. The causes of these effects were analyzed thermodynamically, and it was clarified that the results were due to the activated oxygen sources and the stability level of precursor materials in the solution.

Switching Mode and Mechanism in Binary Oxide Resistive Random Access Memory Using Ni Electrode

2013-02-13T09:00:00+09:00

Authors: Kuan-Liang Lin, Tuo-Hung Hou, Yao-Jen Lee, Jhe-Wei Chang, Jun-Hung Lin, Jiann Shieh, Cheng-Tung Chou, Tan-Fu Lei, Wen-Hsiung Chang, Wen-Yueh Jang, and Chen-Hsi Lin
Resistive-switching (RS) modes in different CMOS-compatible binary oxides have been shown to be governed by the interplay with the Ni top electrode. Unipolar RS and metallic low-resistance state in polycrystalline HfO_{2} and ZrO_{2} are distinct from the preferential bipolar RS and semiconductive low-resistance state in amorphous Al_{2}O_{3} and SiO_{2}. Backside secondary ion mass spectrometry (SIMS) has shown the formation of Ni filaments in HfO_{2}, in contrast to the formation of oxygen-vacancy filaments in Al_{2}O_{3}. The differences have been explained by strong dependence of Ni migration on the oxide crystallinity. Additionally, the RS mode can be further tailored using bilayer structures. The oxide layer next to the Si bottom electrode and its tendency of forming Ni filaments play significant roles in unipolar RS in the bilayer structures, in support of the conical-shape Ni filament model where the connecting and rupture of filaments for unipolar RS occur at the smallest diameter near the bottom electrodes.

Electrochemical Characterization of Hydrothermally Synthesized Pt–Ru–Ni–P Catalyst for Direct Methanol Fuel Cell

Seok-Hee Lee, Dong-Joo Kim, and Young-Soo Yoon — 2013-02-13T09:00:00+09:00

Authors: Seok-Hee Lee, Dong-Joo Kim, and Young-Soo Yoon
Pt–Ru–Ni–P/multiwalled carbon nanotube (MWCNT) catalyst is synthesized by a hydrothermal process using sodium hypophosphite (NaH_{2}PO_{2}) as a reducing agent. The particle size is evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrocatalytic activity of a Pt–Ru–Ni–P/MWCNT catalyst for methanol electro-oxidation has been studied by cyclic voltammetry, chromoamperometry, and impedance spectroscopy. TEM images reveal that the Pt–Ru–Ni–P nanoparticles have a wide size distribution with an average size of 3.2 nm. Pt–Ru–Ni–P/MWCNT catalyst shows an electrochemically active surface area of 63.2 m^{2} g^{-1} and a mass activity of 187.56 mA mg Pt^{-1}. It has been found that the presence of phosphorus as an interstitial species can enhance the dispersion as well as reduce the size of Pt–Ru–Ni–P nanoparticles. Moreover, incorporation of phosphorus into the Pt–Ru–Ni/MWCNT catalyst shows a 1.5 times higher electrocatalytic activity. The power density (57 mW cm^{-1}) of the Pt–Ru–Ni–P/MWCNT catalyst in fuel cell tests is higher than that (40 mW cm^{-1}) of the Pt–Ru–Ni/MWCNT catalyst.

High Purity and Yield Separation of Semiconducting Single-Walled Carbon Nanotubes Dispersed in Aqueous Solutions with Density Gradient Ultracentrifugation Using Mixed Dispersants of Polysaccharides and Surfactants

2013-02-13T09:00:00+09:00

Authors: Koji Tsuchiya, Katsumi Uchida, Yoshiya Kaminosono, Kazushi Shimizu, Tadahiro Ishii, and Hirofumi Yajima
The heterogeneity of as-synthesized single-walled carbon nanotubes (SWNTs) prevents their potential applications in high-resolution field-effect transistors, nanoscale sensors, and conductive films. In the present study, we demonstrate the development of a new selective-separation procedure for collecting semiconducting single-walled carbon nanotubes (s-SWNTs) with a high purity from as-synthesized SWNTs individually dispersed with mixed dispersing agents consisting of carboxymethylcellulose (CMC) and sodium dodecyl sulfate (SDS) in water using density gradient ultracentrifugation (DGU). Ultraviolet–visible–near infrared (UV–vis–NIR) absorption, resonance Raman, and NIR photoluminescence spectroscopies revealed that the s-SWNTs were enriched to a purity of more than 97%, and that the recovery was approximately 40% through the DGU treatment. This separation strategy is expected to impact the application fields using s-SWNTs.

Determining the Thickness of Pb Film Similar to Bulk with Energy Dispersion Derived from Quantum Well States

2013-02-13T09:00:00+09:00

Authors: Wen-Yuan Chan, Hsu-Sheng Huang, Wei-Bin Su, Germar Hoffmann, Shin-Ming Lu, Chia-Seng Chang, Maw-Kuen Wu, and Tien-Tzou Tsong
It is known that the energy spacing between adjacent empty quantum well (QW) states in Pb islands on Cu(111) would reveal the shrinking characteristic originating from the effect of the image potential. Using the phase accumulation model, including a phase factor contributed from the image potential, the shrinking energy spacing can be quantitatively explained with the assumption of the parabolic energy versus wave vector (E–k) dispersion. However, an experimental dispersion acquired from analyzing the energies of the QW state reveals a linear E–k relationship corresponding to the Pb bulk band structure, implying the assumed parabolic dispersion is not appropriate. By combining the linear dispersion with the image potential effect in the calculation, it is found that the calculated values of energy spacing of island thickness below eight atomic layers are not in agreement with the experimental measurements. This implies that the electronic structure of Pb islands would be similar to that of the bulk when their thicknesses reach eight-atomic layers.

Structural Deformation of Graphene–Nanotube Contacts: First-Principles Simulations

Wanli Ma and Gang Zhang — 2013-02-12T09:00:00+09:00

Authors: Wanli Ma and Gang Zhang
By using first-principles simulations, we studied the geometry deformation of few-layer graphene and single-walled carbon nanotube (SWNT) contact. With SWNT on the graphene, the graphene interlayer spacing reduces. Moreover, there is a dip appears in the topmost graphene layer due to the interaction with SWNT. The depth of this dip increases with SWNT diameter. And geometry deformation is also observed in thin SWNT. We demonstrate that even for very thin SWNT, the geometry deformation and flexibility of both graphene layer and SWNT cannot be ignored, which will lead to atomic scale locking of the nanotube on graphene. Thus the contact between SWNT and graphene is more stable than expected.

Influence of Misfit Strain on Longitudinal Electro-optic Properties in Preferentially Oriented (Pb,La)(Zr,Ti)O_{3} Films

Jong-Min Oh, Takuya Hoshina, Hiroaki Takeda, and Takaaki Tsurumi — 2013-02-12T09:00:00+09:00

Authors: Jong-Min Oh, Takuya Hoshina, Hiroaki Takeda, and Takaaki Tsurumi
We successfully fabricated single-crystal-like (Pb,La)(Zr,Ti)O_{3} (PLZT) films with preferred (100), (110), and (111) orientations on Al-doped ZnO (AZO) coated on (100), (110), and (111) SrTiO_{3} (ST) substrates. The longitudinal electro-optic (LEO) effect according to crystal orientation was investigated to find the birefringence origin of the LEO effect in oriented PLZT films. The PLZT films with (100) and (111) orientations exhibit promising LEO properties, while in the case of (110)-oriented PLZT films, the LEO effect is very small. From the strain-induced EO effect, this difference in LEO properties in these three kinds of preferentially oriented PLZT films may be attributed to changes in the strain effect from in the PLZT/AZO interfaces. Consequently, we believed that a misfit strain in interfaces between EO films and transparent conductive oxide films is a birefringence origin in oriented films, and control of the misfit strain is a key factor for improving the LEO effect.

Chemical Etching Using KOH Aqueous Solution for Corona-Charge Micropatterning of Soda-Lime Glass

Daisuke Sakai, Kenji Harada, Daisuke Barada, and Takashi Fukuda — 2013-02-12T09:00:00+09:00

Authors: Daisuke Sakai, Kenji Harada, Daisuke Barada, and Takashi Fukuda
The selectivity of chemical etching for a soda-lime glass substrate to which a micropatterned electric field is applied by corona-charging treatment was investigated. A grating pattern with a period of 4 µm was transferred in a soda-lime glass substrate via corona-charging treatment with a mask template. A diffraction efficiency of 0.02% was detected from the refractive index grating in a template-removed glass substrate. A surface relief grating with a period of 4 µm was fabricated on the glass substrate by selective etching using KOH aqueous solution. The etching rate of the corona-charge-treated domain of the glass substrate was 1.6 times higher than that of normal glass. An enhancement of the etching rate of the glass substrate by the corona-charging treatment occurred up to a depth of approximately 200 nm from the surface. After the surface structural change from the refractive index grating, diffraction efficiency increased to 1.64%, which was 80 times higher than that before chemical etching.

Fast Imaging Ellipsometer Using a LiNbO_{3} Electrooptic Crystal

Lianhua Jin, Riyouma Yagi, Kuniharu Takizawa, and Eiichi Kondoh — 2013-02-12T09:00:00+09:00

Authors: Lianhua Jin, Riyouma Yagi, Kuniharu Takizawa, and Eiichi Kondoh
The LiNbO_{3} electrooptic crystal has been used as a phase modulator in polarimetry for fast single-point measurements. This paper aims to extend the application of the LiNbO_{3} electrooptic crystal to the two-dimensional polarimetric measurement and develop a fast imaging ellipsometer using the crystal. Ellipsometric imaging is made from intensity images measured at four-step phase modulation. The initial birefringence variance of the LiNbO_{3} electrooptic crystal across the view field is compensated by using a calibration sample. A complete image measurement is performed in 3.5 s. An Au-sputtered glass plate and a silicon wafer deposited with a patterned aluminum film are measured to examine the functionality of this ellipsometer. The measurement results show the feasibility of the application of this system to the qualitative measurements of samples.

Enlargement of Grains of Silica Colloidal Crystals by Centrifugation in an Inverted-Triangle Internal-Shaped Container

Kaori Hashimoto, Atsushi Mori, Katsuhiro Tamura, and Yoshihisa Suzuki — 2013-02-08T09:00:00+09:00

Authors: Kaori Hashimoto, Atsushi Mori, Katsuhiro Tamura, and Yoshihisa Suzuki
We successfully fabricated large grains of silica colloidal crystals in an inverted-triangle internal-shaped container (inverted-triangle container) by centrifugation. The largest grain in the container was much larger than that in a container which has a flat bottom and constant width (flat-bottomed container). The edged bottom of the inverted-triangle container eliminated the number of the grains, and then the broadened shape of the container effectively widened the grains.

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