New insight on the role of localisation in the electronic structure of the Si(111)(7\u2009\xd7\u20097) surfaces

M E Dávila,M C Asensio,D P Woodruff,D B Putungan,J Ávila,I R Colambo

doi:10.1038/s41598-021-94664-w

Abstract

New angle-resolved photoelectron spectroscopy (ARPES) data, recorded at several different photon energies from the Si(111)(7 × 7) surface, show that the well-known S1 and S2 surface states that lie in the bulk band gap are localised at specific (adatom and rest atom) sites on the reconstructed surface. The variations in the photoemission intensity from these states as a function of polar and azimuthal emission angle, and incident photon energy, are not consistent with Fermi surface mapping but are well-described by calculations of the multiple elastic scattering in the final state. This localisation of the most shallowly bound S1 state is consistent with the lack of significant dispersion, with no evidence of Fermi surface crossing, implying that the surface is not, as has been previously proposed, metallic in character. Our findings highlight the importance of final state scattering in interpreting ARPES data, an aspect that is routinely ignored and can lead to misleading conclusions.

Highlights

The continuing push for higher and higher degrees of integration in electronic devices, together with the emergence of novel two-dimensional (2D) layer materials such as silicene and graphene, are driving an increasing need to understand the electronic structure of materials confined to a thickness of only a few atomic layers[1]
angle-resolved photoelectron spectroscopy (ARPES) has been used in a number of studies to investigate the properties of the two surface states present on the (7 × 7) reconstructed Si(111) surface, which are generally believed to be 2D itinerant band states with a characteristic 2D Fermi surface being mapped by this technique
Studies of ARPES from itinerant band states in m etals[12] and cuprate s uperconductors[13] have demonstrated the importance of this final state scattering, but the results presented here highlight how neglecting this effect can lead to misleading conclusions regarding the electronic structure

Summary

Introduction

The continuing push for higher and higher degrees of integration in electronic devices, together with the emergence of novel two-dimensional (2D) layer materials such as silicene and graphene, are driving an increasing need to understand the electronic structure of materials confined to a thickness of only a few atomic layers[1]. The intensity variations of the surface state emission recorded in ARPES is shown to be dominated by final-state photoelectron scattering consistent with localised emission from two distinctly different atomic sites within the reconstructed surface.

Results

Conclusion