STM and LEED investigation of the self-assembled Si nanostructures at Ag(110) surface

The quest for silicon-based materials with atoms arranged in a 2D honeycomb structure like graphene, i.e. silicene, has revived the interest for the Si/Ag(110) system which forms remarkable linear nanostructures, coined, "silicon nanoribbons". We present a systematic investigation by Scanning Tunneling Microscopy and Low Energy Electron Diffraction of the Si/Ag(110) system as a function of deposited silicon amount and deposition temperature. Such systematic investigation reveals a complex interplay between the deposited Si amount and deposition temperature, resulting in a rich existence diagram of self-assembled nanostructures and surface reconstructions. Several novel findings are discussed in this work which call for a revisitation of the theoretical structural models and clarify contradicting results reported in literature. In particular, the deposition temperature is demonstrated to be a key parameter to control the width of the produced Si nanoribbons: 0.8 nm-wide nanoribbons are obtained for deposition temperatures lower than 460 K, whereas for temperature higher than 460 K the majority of nanoribbons is 1.6 nm-wide. Interestingly, the massive linear nanostructures recently reported to be "multilayer silicene" nanoribbons, and supposed to form as the deposited silicon amount exceeds full coverage, are also observed at low silicon coverage as the deposition temperature is increased above 460 K. On the other hand, for Si amount higher than one monolayer the surface presents a certain degree of disorder with patches of c(8×4) reconstruction, that are demonstrated to be responsible for the ×4 periodicity detected by LEED measurements and not adequately interpreted in previous papers. Finally, the large collection of Scanning Tunnelling Microscopy images acquired for the systematic study as a function of the different preparation parameters allowed also, based on a sound statistical analysis, to single out image artifacts that may explain contradicting results appeared in previous papers.