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

Amanda Generosi,Bruno Olivieri,Claudio Quaresima,Paola De Padova,Mieczysław Jałochowski,Carlo Ottaviani,Mariusz Krawiec,Barbara Paci,David Garagnani

doi:10.3390/ma15051730

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.

Highlights

Graphene symmetry determines some of its peculiar physical properties such as electronic structures
The electrons behave as Dirac Fermions [3], i.e., as relativistic massless particles exhibiting a linear energy band dispersion at high symmetry points K and K0 in the hexagonal Brillouin zone (BZ)
After the initial studies carried out on Si(111) 3 × 3R30◦ -Bi interface [29–44] to date [28,45,46], great effort has been made both from a theoretical and an experimental point of view to understand the atomic arrangement of Bi atoms [28–46]

Summary

Introduction

The existence of a 2D crystal was initially identified in carbon atoms in 2004 [1], for which the Nobel. Graphene is a single sheet of carbon atoms arranged in a honeycomb lattice, due to its preferential sp hybridization atomic orbitals in a 2D sheet. Graphene symmetry determines some of its peculiar physical properties such as electronic structures. The electrons behave as Dirac Fermions [3], i.e., as relativistic massless particles exhibiting a linear energy band dispersion at high symmetry points K and K0 in the hexagonal Brillouin zone (BZ). Graphene has a high electronic mobility, which makes it an ideal candidate for electronic devices, even if the tailoring of its electronic property is counteracted by the absence of gaps in K and K0 at its inequivalent Dirac points, where its linear bands meet the Fermi level

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Results

Conclusion