Germanene structure enhancement by adjacent insoluble domains of lead

The discovery of graphene has spurred great interest in the growth of a monatomic layer with a honeycomb lattice, the analogs of which belong to the family of two-dimensional (2D) Xenes. However, from the experimental side, 2D Xenes must be grown on a substrate, which usually hinders the formation of a freestanding Xene, leaving the epitaxial growth of 2D Xenes with high lattice quality and intrinsic electronic structures a tremendous challenge.

Germanene has been successfully grown on Ag(111) in two phases: the striped ph ase (SP) and the quasi-freestanding phase (QP). We report the discovery of an interesting recipe for enhancement of epitaxially grown monatomic layers on a lattice-mismatched substrate using chemical pressure between an insoluble monatomic layer and an existing Xene, in our case monatomic Pb layer and QP germanene on Ag(111). Using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM), we demonstrate that the 2D monatomic Pb layer, instead of being on top, grows side-by-side with QP germanene, not only driving the SP-to-QP transition but further enhancing the lattice order of QP as revealed by the dramatic evolution of LEED-spot shape and uniform STM-imaged array of moiré patterns. The higher-order coincidence (HOC) density analysis for both monatomic layers on Ag(111) shows that the further rotation of both converts them to more favorable configurations that also produce improved lattice order and more intrinsic electronic structures.