Surface oxides on Pd(111) : STM and density functional calculations

摘要: The formation of one-layer surface oxides on Pd(111) has been studied by scanning tunneling microscopy (STM) and density functional theory (DFT). Besides the ${\mathrm{Pd}}_{5}{\mathrm{O}}_{4}$ structure determined previously, structural details six different will be presented. These are observed for preparation in oxygen-rich conditions, approaching thermodynamic stability limit PdO bulk oxide at an oxygen chemical potential $\ensuremath{-}0.95\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}\ensuremath{-}1.02\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ ($570--605\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\phantom{\rule{0.3em}{0ex}}\mathrm{mbar}$ ${\mathrm{O}}_{2}$). Sorted increasing fraction primitive unit cell, stoichiometry is ${\mathrm{Pd}}_{5}{\mathrm{O}}_{4}$, ${\mathrm{Pd}}_{9}{\mathrm{O}}_{8}$, ${\mathrm{Pd}}_{20}{\mathrm{O}}_{18}$, ${\mathrm{Pd}}_{23}{\mathrm{O}}_{21}$, ${\mathrm{Pd}}_{19}{\mathrm{O}}_{18}$, ${\mathrm{Pd}}_{8}{\mathrm{O}}_{8}$, ${\mathrm{Pd}}_{32}{\mathrm{O}}_{32}$. All structures oxides, which atoms form a rectangular lattice, all follow same rules favorable alignment layer substrate. DFT calculations were used to simulate STM images as well determine structures. Simulated measured excellent agreement, indicating that models correct. Since newly found clearly less stable than we conclude only thermodynamically phase, whereas kinetically stabilized. We also discuss possible mechanisms these