Reversible hydrogenation of silicene

The hydrogenation of monoatomic silicene sheet on Ag(111) was studied by scanning tunneling microscopy and density functional theory calculations. It was observed that hydrogenation of silicene-4x4 structure at room temperature results in a perfectly ordered $\gamma $-4x4 superstructure. A theoretical model, which involves 7 H atoms and rearranged buckling of Si atoms, was proposed and agrees with experiments very well. Unlike silicene-4x4, the hydrogenation of ($\surd $7x$\surd $7)silicene/(2$\surd $3x2$\surd $3)R30$^{\circ}$Ag(111) superstructure at room temperature shows silicene-1x1 structure with $\surd $7x$\surd $7 reconstruction Moreover, by annealing to a moderate temperature, about 450 K, de-hydrogenation process occurs and the clean silicene surface can be fully recovered. Such reversible hydrogenation suggests that silicene may be a potential candidate as hydrogen storage materials.