Hydrogenation of silicene films grown on Ag(111)

We have investigated the effect of hydrogen interaction with silicene monolayer and multilayer films grown on Ag(111) by means of scanning tunneling microscopy, low energy diffraction and high-resolution electron energy loss spectroscopy. On monolayer silicene, we demonstrate that the recently reported hydrogenated gamma-(3 x 3) is indeed observed, but is found often in coexistence with the usual flower pattern of the clean silicene-(3 x 3), also labeled alpha-(3 x 3). In the vibrational spectra, features related to Si-H vibrational modes show shifts towards lower energies as compared to hydrogenated Si surfaces. This substantial bond softening is indicative of a partial charge filling of the bonding or anti-bonding orbitals of the Si-H bonds as compared to Si(111) H. Indirectly, this is an evidence of the hybridization of monolayer silicene with the Ag(111) substrate. At multilayer coverage, the situation is clearly different. Indeed, hydrogen strongly perturbs the root 3 x root 3 reconstruction of the multilayer film, leading to its local dissolution and to the formation of protrusions due to clustering of atoms. The vibrational spectrum of the root 3 x root 3 silicene closely resembles that of a highly hydrogenated Si surfaces, with the simultaneous presence of Si-H, Si-H-2 and Si-H-3 bonds. (C) 2016 Elsevier B.V. All rights reserved.