Temperature-dependent multilayer relaxation of clean and hydrogen-dosed Nb(100)
| Autor: | D. Lacina, James L Erskine |
|---|---|
| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | Physical Review B. 76 |
| ISSN: | 1550-235X 1098-0121 |
| DOI: | 10.1103/physrevb.76.104103 |
| Popis: | Low-energy-electron-diffraction intensity measurements and multiple scattering analysis are used to determine the multilayer surface relaxation of clean and hydrogen-dosed Nb(100) as a function of temperature. Accurate characterization of residual surface impurity concentration (oxygen) based on Auger electron spectroscopy is used to obtain a meaningful extrapolation of the first-layer relaxation to the clean surface value: ${d}_{12}=1.481\ifmmode\pm\else\textpm\fi{}.05\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ corresponding to ${\ensuremath{\Delta}}_{12}=\ensuremath{-}10\ifmmode\pm\else\textpm\fi{}3%$, a 10% relaxation relative to the bulk value ${d}_{0}=1.645\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. This experimental result for ${d}_{12}$ can be used to judge the accuracy of recent ab initio calculations for Nb(100). Temperature-dependent changes in surface relaxation resulting from hydrogen dosing of Nb(100) manifest an expansion of the near-surface lattice resulting from subsurface hydrogen atoms. The hydrogen-induced expansion of near-surface interplanar separation is determined to be $3\ifmmode\pm\else\textpm\fi{}1%$ at $T=125\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, $4\ifmmode\pm\else\textpm\fi{}1%$ at $T=300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and $\ensuremath{-}1\ifmmode\pm\else\textpm\fi{}1%$ at $T=400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The measured hydrogen-induced surface lattice expansion is consistent with the bulk lattice constant change $(\ensuremath{\Delta}\ensuremath{\sim}4.5%)$ that occurs when Nb is hydrated to form $\ensuremath{\beta}\mathrm{Nb}\mathrm{H}$. The observed relaxation of the hydrogen-dosed near-surface interplanar separation to the clean surface value for $Tg400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is consistent with the subsurface ``hydrogen valve'' model that has been used to account for unusual hydrogen uptake kinetics associated with Nb(100). |
| Databáze: | OpenAIRE |
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