Space-Group Determination of the Low-TemperatureW{001}(2×2)R45°Surface Structure by Low-Energy-Electron Diffraction

Abstract

Low-energy-electron diffraction $I-V$ spectra obtained from the clean, cooled $\mathrm{W}\mathrm{}\left\{001\right\}(\sqrt{2}\times \sqrt{2})R45\mathrm{}°$ surface structure at < 190 K display $2mm$ point-group symmetry, revealing a preferential orienting of equivalent domains. A further novel effect, that the half-order beam spectra ($\pm \frac{h}{2}, \pm \frac{h}{2}$) are identical in relative intensity to the ($\pm \frac{h}{2}, \mp \frac{h}{2}$) spectra but different in absolute intensity by a constant factor, uniquely establishes the space-group symmetry of the domains as $p2\mathrm{mg}$. A structure for a single-layer surface rearrangement is proposed.