The hydrogenation of monatomic silicene sheet on Ag(111) was studied by scanning tunneling microscopy and density functional theory calculations. It was observed that hydrogenation of silicene at room temperature results in a perfectly ordered γ-(3×3) superstructure. A theoretical model, which involves seven H atoms and rearranged buckling of Si atoms, was proposed and agrees with experiments very well. Moreover, by annealing to a moderate temperature, about 450 K, a dehydrogenation process occurs and the clean silicene surface can be fully recovered. Such uniformly ordered and reversible hydrogenation may be useful for tuning the properties of silicene as well as for controllable hydrogen storage.

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We discuss the results of the scanning tunneling microscopy (STM) investigations and ab initio calculations of the structure and stability of the quasicubic Bi{012} film formed in the initial stage of the bismuth deposition on the Si(111)-7×7 surface at room temperature. Results of our STM experiments show that paired-layer Bi{012} film grows on top of the initially formed wetting layer, with the Si 7×7 lattice preserved underneath. The pairing of the layers in the {012} film leads to the substantial stabilization of the film when it consists of an even number of layers and only even-number layered Bi{012} islands are observed to be stable. The buckling of the atoms in the topmost paired layer induced by the relaxation of the film is evidenced by the high-resolution STM images.