  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.
