Residue-free layered material interfaces for device processing

The emergence of two-dimensional (2D) materials has catalysed the development of designer-stacked heterostructures and advanced devices. However, the transfer process of these layers generally involves polymer support, leaving traces of organic residues that can affect the reliability of devices based on them. This surface contamination by polymer residues has been a long-standing critical problem in device processing and fabrication that has not been fully resolved so far despite attempts by various groups. In this study, we employ low-energy electron microscopy (LEEM) as a novel approach to identify nano-sized traces of polymer residues present on the transferred hexagonal boron nitride (hBN) flakes and explore effective elimination strategies. Our results demonstrate the sensitivity of LEEM to detect minute residue traces that are not feasible with the conventional methods. We show the polymer residues on the substrate form fractal-like structures, leading to local work-function variations. Further, we propose a high-temperature annealing approach to achieve clean interfaces validated by LEEM and Raman spectroscopy.