Scanning Tunneling Microscopy Study of Epitaxial Growth of Wafer Scale, Single Atomic Sheet Honeycomb BeO Two-dimensional Insulator*

We report the discovery of a novel 2D insulator comprised of a single atomic sheet honeycomb structure BeO, though its bulk counterpart has a wurtzite structure. Such a single sheet of BeO is grown epitaxially on Ag(111) thin films, also epitaxially grown on Si(111) wafers. Using scanning tunneling microscopy and spectroscopy (STM/S) we observe this novel BeO atomic sheet has a lattice constant of 2.65 Å and a band gap of 6 eV. We also found the BeO has a weak van der Waals (vdW) interaction with the Ag(111) substrate, which agrees well with predictions of our density functional theory calculations. Moiré pattern analysis shows the BeO honeycomb structure maintains long range phase coherence in atomic registry even across Ag steps. This novel material provides a scalable platform for 2D electronics, as an attractive 2D insulator due to its potentially much higher thermal conductivity than that of hBN. More significantly, the ability to create a single crystalline atomic sheet with no bulk counterpart of similar structure opens a new avenue toward tailoring novel 2D electronic materials.