Two-Dimensional One-Atom-Thick Gold Grown on Defect-Engineered Graphene

In this work, a general route to creating two-dimensional, one-atom-thick metal layers, metallene, on functionalized graphene is proposed. To explore its viability, low-energy ion irradiation is performed to introduce vacancies into initially pristine graphene, followed by ultralow-energy gold irradiation to deposit individual gold atoms onto it. While gold freely migrates on pristine graphene, vacancies provide anchoring points where gold atoms gather and promote the growth of atomically thin nanoplatelets. The physical and chemical structure of the gold flakes is confirmed through atomic-resolution scanning transmission electron microscopy and electron energy loss spectroscopy, while their formation is investigated using ab initio simulations. The thickness and diameter of the gold flakes are directly proportional to gold ion fluence during ultralow-energy ion irradiation. Gold atoms in small gold structures are arranged in a one-atom-thick hexagonal lattice. Larger goldene platelets with lateral sizes in the range of tens of nanometers contain multiple gold layers. Mono- and few-layer flakes are metastable under continuous 60 keV electron irradiation during imaging but occasionally rotate and take small jumps as the atoms at the edges move. A reversible transformation between a flat monolayer and an amorphous three-dimensional gold cluster is observed in the experiments and is also seen in the simulations.