ION SCATTERING STUDIES OF CLEAN Nb(110) SURFACES BEFORE AND AFTER EXPOSURE TO HYDROGEN
Xu Mingde, C.N. Whang*, and R.J. Smith
Physics Department, Montana State University, Bozeman, MT 59717**
The Nb(110) surface was studied using high-energy ion backscattering and channeling
(HEIS) to determine the structure of the clean surface, and to measure changes in structure
induced by H2 adsorption at the surface and absorption into the bulk material. Measurements
with He+ ions channeling in the [110] and [111] directions were made as a function of ion
energy (0.6 to 1.8 MeV) and H2 exposure. Computer simulations of the experiment for the
clean surface show good agreement with the data using negligible enhancement (less than 2%) of the
surface-atom vibration amplitudes, and negligible surface relaxation. To obtain agreement
with experiment does require that the simulations include reduced bulk atom vibration
amplitudes, which simulate the effect of correlated vibrations. Our conclusions are in good
agreement with calculations based on experimental phonon frequencies. As the surface is
exposed to H2, the Nb surface peak area increases by ~12% ( 1 MeV ion energy) in the
chemisorption regime (0 to 20 L), followed by a more gradual increase as the H is absorbed
into the bulk Nb. We discuss possible explanations for these increases in ion yield in the
context of recent models for hydrogen uptake kinetics.
**Work supported by NSF
Journal of Vacuum science and Technology A8(3), 2501 (1990)
* Present address:Physics Department, Yonsei University, Seoul, KOREA
For information on this publication or to request a reprint send mail to smith@physics.montana.edu
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