Germanene, a 2D honeycomb structure similar to silicene, has been fabricated on Al(111). The 2D germanene layer covers uniformly the substrate with a large coherence over the Al(111) surface atomic plane. It is characterized by a (3 × 3) superstructure with respect to the substrate lattice, shown by low energy electron diffraction and scanning tunnelling microscopy. First-principles calculations indicate that the Ge atoms accommodate in a very regular atomic configuration with a buckled conformation.

The electronic structure of germanene is investigated by high resolution photoemission and density functional theory calculations. The core level Al 2p and Ge 3d lines are measured on germanene grown on Al(111) by using synchrotron radiation. The Ge 3d line is shifted toward the low binding energies with respect to bulk Ge, and shows three components, reflecting the sites multiplicity of the germanene atomic structure. The calculations reveal a sizable charge localization at the germanene/Al(111) interface, a charge transfer from the Al surface atoms to the germanene, and the existence of three nonequivalent Ge sites with three different atomic Bader charges, in agreement with the photoemission measurements.

The treatment of Ge(100) in an aqueous ammonium sulfide solution is investigated by means of x-ray photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, scanning electron microscopy, and atomic force microscopy. This treatment is shown to produce an S-passivated Ge(100)-(1×1) surface, where the S atoms appear to be bridge bonded to the Ge atoms. Desorption of the S is observed to occur between 460 and 750 K and results in a Ge(100)-(1×1) surface with a surface morphology similar to that of the initial sample.

A new germanene crystallographic structure is investigated by scanning tunnelling microscopy and density functional theory calculations. We found that germanene can crystallize in two stable but different structures when grown on Al(111) at the same temperature. These structures are evidenced in scanning tunnelling images by a honeycomb contrast and by a hexagonal contrast. These contrasts are relevant of a Ge network with one (hexagonal) or two (honeycomb) Ge atoms per unit cell shifted upward with respect to the other Ge atoms. These structures appear alternatively and can be turned on and off by a tip-induced process.