Multilayer silicene: clear evidence

Abstract

One year after the publication of the seminal paper on monolayer 33 reconstructed silicene grown on a silver (111) substrate, evidence of the synthesis of epitaxial 33 reconstructed multilayer silicene hosting Dirac fermions was presented. Although a general consensus was immediately reached in the former case, in the latter one, the mere existence of multilayer silicene was questioned and strongly debated. Here, we demonstrate by means of a comprehensive x-ray crystallographic study, that multilayer silicene is effectively realized upon growth at rather low growth temperatures (~200°C), while, instead, three-dimensional growth of silicon crystallites takes place at higher temperatures, (~300°C). This transition to bulk like silicon perfectly explains the various data presented and discussed in the literature and solves their conflicting interpretations.

π conjugation in the epitaxial Si(111)- 3×3 surface: Unconventional “bamboo hat” bonding geometry for Si

“…We note that the BHS structure is only more stable than the (2×1) surface when surface is under a tensile strain larger than 1.5%, otherwise it is less stable [34]. This is consistent with the experimental observations that the ( √ 3× √ 3) structure is metastable with a lattice contraction of compressive strain [16][17][18]. The kinetic pathways leading to the formation of ( √ 3× √ 3) structure deserves further attention.…”

“…Also, M3 and M4 were used to explain the Si(100)-(2×1) reconstruction [29]. Here, we will apply some of these same principles to understand the recently observed Si(111)-( √ 3× √ 3) surface [15][16][17][18][19][20][21]. As shown in Fig.…”

“…at a low temperature), but remain dynamically stable at given temperature. This is also the case for the ( √ 3× √ 3) surface, which only forms at low temperature (∼ 200 • C) and to have a compressed lattice constant [16][17][18]. Therefore, to better understand its formation, we next analyze the relative stability of the BHS surface and the bulkterminated (2×1) surface as a function of strain.…”

“…Interestingly, a "planar" hexagonal ring-shaped structure has been observed in the surface of epitaxially grown Si(111)-( √ 3× √ 3) thin films [15][16][17][18][19][20][21], which is dubbed as "multilayer silicene" by some researchers. However, previous first-principles calculations have invalidated a stacked silicene structure, which spontaneously transforms into the bulk sp 3 structure with just two layers of stacking [19,20].…”

“…Based on density functional theory (DFT) calculations [34], we further analyse the effect of strain on surface energies of both ( √ 3× √ 3) and (2×1) superstructures to evaluate their relative stability to elucidate the experimental results [15][16][17]. Finally, we investigate the possible configurations of Si(111)-( √ 21× √ 21) reconstruction as observed in a recent experiment [35], which can also be explained by the π-conjugation and charge-transfer model.…”