Evidence of sp2-like Hybridization of Silicon Valence Orbitals in Thin and Thick Si Grown on α-Phase Si(111)√3 × √3R30°-Bi

Abstract

One-monolayer (ML) (thin) and 5-ML (thick) Si films were grown on the α-phase Si(111)√3 × √3R30°-Bi at a low substrate temperature of 200 °C. Si films have been studied in situ by reflection electron energy loss spectroscopy (REELS) and Auger electron spectroscopy, as a function of the electron beam incidence angle α and low-energy electron diffraction (LEED), as well as ex situ by grazing incidence X-ray diffraction (GIXRD). Scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS) were also reported. The REELS spectra, taken at the Si K absorption edge (~1.840 KeV), reveal the presence of two distinct loss structures attributed to transitions 1s→π* and 1s→σ* according to their intensity dependence on α, attesting to the sp2-like hybridization of the silicon valence orbitals in both thin and thick Si films. The synthesis of a silicon allotrope on the α-phase of Si(111)√3 × √3R30°-Bi substrate was demonstrated by LEED patterns and GIXRD that discloses the presence of a Si stack of 3.099 (3) Å and a √3 × √3 unit cell of 6.474 Å, typically seen for multilayer silicene. STM and STS measurements corroborated the findings. These measurements provided a platform for the new √3 × √3R30° Si allotrope on a Si(111)√3 × √3 R30°-Bi template, paving the way for realizing topological insulator heterostructures from different two-dimensional materials, Bi and Si.

Unpinned Dirac-Fermions in Carbon–Phosphorus–Arsenic-Based Ternary Monolayers

“…Overall, our results clearly indicate that the ternary CPAs 2 monolayers favor a mixture of sp 2 and sp 3 hybridizations corresponding to buckled geometric structure rather than pure sp 2 hybridization of the planar geometry structure. This observation is similar to the one found in buckled monolayers such as silicene, germanene, binaries of groups IV–IV, III–V, and CAs 3 . ,, …”

“…This observation is similar to the one found in buckled monolayers such as silicene, germanene, binaries of groups IV−IV, III−V, and CAs 3 . 28,32,45 In addition, we also perform ab initio molecular dynamics (AIMD) simulations at room temperature (300 K) for a CPAs 2 monolayer, whose results are given in Figure S1 of Supporting Information. The results of AIMD simulations along with a few snapshots indicate that the ternary CPAs 2 monolayer is quite stable at finite temperature.…”

Si(111) islands on β-phase Si(111)√3 × √3R30°-Bi

“…It is attributed to the (111) reflection of the [111] planes of the silicon substrate, overlapped with the stacked layers of the Si film. By simply applying the law of Bragg (2d = nλ sin , where λ is the incident radiation, K α Cu = 1.540 Å, and n = 1 is the order of the reflection), it was found, for both Si substrate and film, d Si(111) = 3.140 Å (5), in close agreement with the values achieved in [33][34][35][36] for Si substrate alone.…”

“…Equally interesting is the silicene system, a honeycomb layer of one layer of Si atoms, buckled [27] or flat [28] , or an ensemble of stacks of silicene layers, called multilayer silicene [29][30][31][32][33][34][35][36] .…”

Epitaxial growth and structural properties of silicene and other 2D allotropes of Si

“…Lattice constants were very similar to those obtained for the Ag-covered Si(111) substrate. 176 5.4 Thin silicon lms/other substrates Ordered phases were observed by STM and micro-LEED aer evaporating, at 593 K, up to 9 ML of Si on a silicene layer grown by segregation through a ZrB 2 (0001)/Si(111) lm. 177 Unfortunately, no structural characterization of the lms by XRD has been performed up to now.…”