Epitaxial growth of a two-dimensional topological insulator candidate: monolayer Si2Te2

TL;DR

This study reports the successful epitaxial growth of monolayer Si2Te2 on Sb2Te3 substrates, confirming its semiconducting properties and potential as a topological insulator through experimental and theoretical analysis.

Contribution

First experimental realization of high-quality monolayer Si2Te2, enabling exploration of its topological insulator properties previously only predicted theoretically.

Findings

High-quality ML-Si2Te2 films achieved with 95% coverage

Confirmed semiconducting band structure via spectroscopy and calculations

Predicted strain engineering can induce nontrivial topological phase

Abstract

Hexagonal Si2Te2 monolayers (ML-Si2Te2) were predicted to show strain-dependent band-crossover between semiconducting and room-temperature quantum spin Hall phases. However, investigations on this artificial two-dimensional (2D) material have mainly been restricted to theoretical calculations because its bulk counterpart does not exist naturally. Here, we report on the successful epitaxial growth of ML-Si2Te2 films on Sb2Te3 thin film substrates. High-quality (1*1) ML-Si2Te2 films with a coverage as high as 95% were obtained as revealed by scanning tunneling microscopy. X-ray photoelectron spectroscopy confirms the absence of intermixing between Si2Te2 and Sb2Te3 at the interface. By combining scanning tunneling spectroscopy with density functional theory calculations, we demonstrate the semiconducting band structure of ML-Si2Te2 on Sb2Te3. Furthermore, it is theoretically predicted that the system can be driven into the nontrivial phase via reducing the strain by 4.4% using strain engineering. Our results pave the way for in-depth investigations on this 2D topological insulator candidate.