Single germanene phase formed by segregation through Al(111) thin films on Ge(111)

Abstract

We have obtained single phase monolayer germanene on aluminum (111) thin films grown on a germanium (111) template by atomic segregation epitaxy, a preparation method differing from molecular beam epitaxy used in previous works. This 2 × 2 reconstructed germanene phase matching an Al(111)3 × 3 supercell has been prepared in large areas upon annealing at 430 °C. Detailed studies have been carried out using scanning tunneling microscopy (STM), low-energy electron diffraction, Auger electron spectroscopy, and synchrotron radiation photoemission spectroscopy. First-principles calculations based on the density function theory along with atomic-scale STM images reveal the atomic structure with one protruding Ge atom per 2 × 2 germanene supercell and a characteristic dispersing band originating from the germanene sheet slightly coupled to the first layer Al atoms underneath. Instead, upon annealing at lower temperatures, multi-phase regions comprise twisted germanene domains in correspondence with an Al(111)√7×√7 R ± 19.1° superstructure as obtained in previous studies.