Phase transition of theAg∕Si(111)−(3×3)surface studied by photoelectron diffraction

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The local atomic structure of the Ag induced $\mathrm{Si}(111)\text{\ensuremath{-}}(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$ surface has been investigated using photoelectron diffraction (PED) at 10 and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Two surface components, whose intensities varied by changing the photon energy as a consequence of diffraction effects, were observed in the $\mathrm{Si}\phantom{\rule{0.3em}{0ex}}2p$ core-level spectra at both temperatures. The good agreement between the experimental PED patterns of the $\mathrm{Si}\phantom{\rule{0.3em}{0ex}}2p$ surface components and the simulated PED patterns indicates that the atomic structure of this surface follows the inequivalent triangle model. Further, since the PED patterns obtained at 10 and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ resemble each other closely, we conclude that the local atomic structure of the $\mathrm{Ag}∕\mathrm{Si}(111)\text{\ensuremath{-}}(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})$ surface is the same at the two temperatures, and thus that the origin of the transition reported in the literature is an order-disorder transition.