Process Pathway Controlled Evolution of Phase and Van‐der‐Waals Epitaxy in In/In₂O₃ on Graphene Heterostructures

Abstract

Many applications of 2D materials require deposition of non-2D metals and metal-oxides onto the 2D materials. Little is however known about the mechanisms of such non-2D/2D interfacing, particularly at the atomic scale. Here, atomically resolved scanning transmission electron microscopy (STEM) is used to follow the entire physical vapor deposition (PVD) cycle of application-relevant non-2D In/In₂O₃ nanostructures on graphene. First, a “quasi-in-situ” approach with indium being in situ evaporated onto graphene in oxygen-/water-free ultra-high-vacuum (UHV) is employed, followed by STEM imaging without vacuum break and then repeated controlled ambient air exposures and reloading into STEM. This allows stepwise monitoring of the oxidation of specific In particles toward In₂O₃ on graphene. This is then compared with conventional, scalable ex situ In PVD onto graphene in high vacuum (HV) with significant residual oxygen/water traces. The data shows that the process pathway difference of oxygen/water feeding between UHV/ambient and HV fabrication drastically impacts not only non-2D In/In₂O₃ phase evolution but also In₂O₃/graphene out-of-plane texture and in-plane rotational van-der-Waals epitaxy. Since non-2D/2D heterostructures' properties are intimately linked to their structure and since influences like oxygen/water traces are often hard to control in scalable fabrication, this is a key finding for non-2D/2D integration process design.