Growth mechanism of silicene onAg(111)determined by scanning tunneling microscopy measurements andab initiocalculations

Abstract

Scanning tunneling microscopy has been used to real-time study the growth of silicene on Ag(111) in the 200-533-K temperature range. We show that the growth mode depends strongly on the deposition temperature T. At T = 300 K and above, the formation of silicene results from the exchange between surface Ag atoms and Si atoms, which are inserted in the substrate top layer. Density functional theory calculations confirm that Si insertion is thermodynamically favored, and we propose an energetic model for explaining the observed growth processes as a function of T. For T 400 K, ordered structures are observed as soon as silicene domains are large enough. With increasing coverage, disordered and dotted phases progressively transform into stable (√ 13 × √ 13)R13.9 • and (4 × 4) structures.

Scanning tunnelling spectroscopy and Raman spectroscopy of monolayer silicene on Ag(111)

“…1(c)). The two other structures that also grow at the same time are identified as the (4 × 4) and (√13 × √13 − α) silicene phases in agreement with the structures observed in the temperature range of 230-250°C [5,18,19]. We note that the proportion of the (√13 × √13 − β) phase with respect to the two other phases decreases as the coverage approaches 1 ML.…”

“…1 shows the evolution of the surface as the Si coverage increases. At low coverage, the surface consists of strips that form at step edges, consistent with the literature for similar growth temperatures [18]. The baseline of the strips is lower than the upper silver terrace.…”

Determining the atomic structure of the ( 4×4 ) silicene layer on Ag(111) by combined grazing-incidence x-ray diffraction measurements and first-principles calculations

“…Silver appears to be appropri-ate for silicene growth since: (i) the Ag-Si phase diagram shows non-miscibility of the solid phases, (ii) Ag and Si lattice constants are in 3/4 ratio and (iii) their similar electronegativity should result in a small charge transfer between the Si layer and the substrate. However, joint experimental studies and DFT calculations have revealed a non-negligible interaction between Si and Ag [24,[27][28][29][30][31] which results in the loss of the electronic properties predicted for the FSS. Depending on both deposition rate and temperature [15,16,19,27] …”

Formation of silicene on silver: Strong interaction between Ag and Si

“…A first identification in 2007 of a ‘graphitic silicon layer’ was proposed on Ag(100) , followed by the observation of ordered Si nanoribbons on Ag(110), and from 2010, several structures of Si on Ag(111) were described as silicene layers with different epitaxial orientations on the substrate . However, it has been shown recently that large interaction occurs between the silicene layer and the Ag substrate, whether it is on the (110) or on the (111) surface , leading to an hybridisation of the Ag and of the silicene states .…”

“…These findings show that, during deposition, the interaction between Si and Ag substrate is much more important than what was originally thought. This, therefore, questions the actual structure of some of the phases observed during the formation of the Si layer, and for which the formation of a Si–Ag surface alloy during growth is now also considered .…”