High Resolution Electron Energy Loss Spectroscopy Studies of Clean and Hydrogen Covered Tungsten (100) Surfaces.
Abstract
High resolution (10 meV FWHM) low energy ((LESSTHEQ)100 eV) electrons are scattered from the tungsten (100) surface. Electron energy loss spectroscopy (EELS) selection rules are utilized to identify vibrational modes of the surface tungsten atoms. A 36 meV mode is measured on the c(2 x 2) thermally reconstructed surface and is modeled as an overtone of the 18 meV mode at (')M in the surface Brillouin zone. The superstructure of the reconstructed surface allows this mode to be observed in specular scattering. The surface tungsten atoms return to their bulk lateral positions with saturated hydrogen ((beta)(,1) phase) adsorption; and a 26 meV mode is identified which is due to the per- pendicular vibration of the surface tungsten layers. The clean room temperature surface does not display either low energy vibrations and the surface is modeled as disordered. The three (beta)(,1) phase hydro - gen vibrations are observed and a new vibration at 118 meV is identi- fied. The 118 meV cross section displays characteristics of a parallel mode, but calculations show this assignment to be erroneous. The mode disperses upward toward the 130 meV perpendicular hydrogen vibration in the (')(GAMMA)(')X direction. There are two hydrogen atoms for each surface tungsten atom in the (beta)(,1) phase, and lattice dynamical calcu- lations show that the 118 meV mode is due to a hydrogen zone edge vibration. The predicted breakdown of the parallel hydrogen vibration selection rule has not been observed.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1986
- Bibcode:
- 1986PhDT........86W
- Keywords:
-
- Physics: Condensed Matter