Jpn. J. Appl. Phys. 18 (1979) pp. 1223-1229 |Next Article| |Table of Contents|
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Coadsorption of Thorium and Hydrogen on a Tungsten Surface
Nagasaki Institute of Applied Science
(Received January 10, 1979)
The coadsorption of thorium and hydrogen on a tungsten surface has been investigated with a field emission microscope (FEM). When the coverage of thorium (θTh)is less than half a monolayer, the work function of the surface decreases with θTh owing to the formation of surface complexes such as WH-Th+ by the adsorption of hydrogen on the Th-covered tungsten surface. The maximum decrease in work function is found to be 0.23 eV at θTh=θH=0.5, when the number of the surface complex, WH-Th+, is largest. When θTh is larger than half a monolayer, the change in the work function (Δφ) decreases; it becomes zero at θTh=0.64. Thus, when θH=0.5, the curve for Δφ vs. θTh is symmetrical about the point θTh=0.5. When the coverage of hydrogen is larger than 0.5, Δφ also decreases owing to the increase in the number of the surface complex, Th+H-, on the coadsorption surface. The sticking probability of hydrogen on a tungsten surface covered with Th is found to be 0.025 to 0.05, half that on a clean tungsten surface. When the coadsorbed surface is heated to 900∼1000 K, only the hydrogen is desorbed, with an activation energy of 2.36 eV, comparable to that on a clean tungsten surface.
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