Structure of germanene/Al(111): a two-layers surface alloy

TL;DR

This study clarifies the true structure of germanene on Al(111), revealing it is a mixed Ge-Al alloy layer rather than a pure germanene monolayer, challenging previous interpretations based on surface reconstruction.

Contribution

The paper provides a combined experimental and theoretical analysis showing the (3 x 3) surface reconstruction is a mixed Ge-Al alloy, not pure germanene, refining understanding of germanene growth on Al(111).

Findings

The (3 x 3) reconstruction is a mixed Ge-Al honeycomb layer.

Pure germanene monolayer on Al(111) can be excluded.

Surface X-ray diffraction and DFT support the alloy model.

Abstract

Unlike silicene, for which the demonstration of its existence has been done through numerous independent studies, the possibility of growing epitaxial germanene remains highly controversial. It has been recently shown by scanning tunneling microscopy that the (3 x 3) surface reconstruction formed upon Ge deposition on Al(111) presents a honeycomb structure, and it was assigned to a pure germanene monolayer. Using quantitative measurements by surface X-ray diffraction compared to density functional theory calculations, we demonstrate that this Ge/Al(111) (3 x 3) reconstruction corresponds, in fact, to a mixed Ge--Al honeycomb layer on top of an alloyed interfacial layer. The model of a germanene monolayer on top of the Al(111) surface can be completely excluded.