Evidence of sp2-Like Hybridization of Silicon Valence Orbitals in Thin and Thick Si Grown on alpha-Phase Si(111) ?3x ?3R30°-Bi

One-monolayer (ML) (thin) and 5-ML (thick) Si films were grown on the alpha-phase Si(111) ?3x ?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 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-Pi* and 1s-sigma* according to their intensity dependence on alpha, 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 alpha-phase of Si(111) ?3x ?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 ?3x ?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 ?3x ?3R30°-Bi Si allotrope on a Si(111) ?3x ?3R30°-Bi-Bi template, paving the way for realizing topological insulator heterostructures from different two-dimensional materials, Bi and Si.