Structural and electronic properties of the α-GeSe surface

We have investigated the structural and electronic properties of the α-GeSe surface using atomic force microscopy, scanning tunneling microscopy and density functional theory calculations. GeSe belongs to the group-VI transition metal monochalcogenides and occurs in two polymorphs, α-GeSe and β-GeSe. The most redundant polymorph, α-GeSe, has a structure that is very similar to black phosphorene. The α-GeSe surface has a centered rectangular unit cell with dimensions a = 3.8 Å and b = 4.4 Å respectively. In scanning tunneling microscopy images only the Se atoms are resolved owing to the substantial transfer of electrons from the Ge to the Se surface atoms. This experimental finding is fully in line with density functional theory calculations. Scanning tunneling spectroscopy reveals that the α-GeSe surface is a p-type semiconductor with a band gap of 1.0 eV. The GeSe surface is stable at ambient conditions, which makes this material very appealing for technological applications.