α-Ga(010) surface reconstruction: A LEED structural analysis of the(1×1)room temperature and(22×2)R45°low-temperature structures

The geometric structure of the $\alpha -\mathrm{Ga}\mathrm{}\left(010\right)\mathrm{}-(1\mathrm{}\times 1)$ room temperature structure and its $(2\mathrm{}\sqrt{2}\times \sqrt{2})\mathit{R}45°$ reconstruction below 232 K have been determined using low-energy electron diffraction structure analysis. The room temperature structure conforms to the cut-dimer model, forming a two-dimensional metallic structure with only minimal lateral displacements of the atoms. The topmost interlayer distance is 1.53 Å, corresponding to a spacing expansion of 2% from the bulk. In the low-temperature structure, the surface atoms shift to dimerize within the top two layers, resulting in a network of mostly covalent bonds, which form both parallel and perpendicular to the surface plane. The bond lengths of some of these dimers are about 10% shorter than the bond length found in the $\alpha$-Ga bulk and are thus shorter than any $\mathrm{Ga}—\mathrm{Ga}$ bonds reported so far.