Adhesion-induced MoS2 layer transfer via in-situ TEM-nanoindentation: Effects of curvature and substrate mediated residual stress

Abstract

Molybdenum disulfide (MoS₂) holds great potential in a wide range of applications, including electronics, photodetectors, light-emitting diodes (LEDs), and solar cells due to its unique two-dimensional (2D) structure. This structure enables innovative functionalities, particularly in flexible and wearable technologies. However, a significant knowledge gap remains regarding MoS₂'s interfacial adhesion, a critical aspect for advancing next-generation devices. To address this, we conducted a comprehensive study investigating the interaction forces originating from the bonding between atoms that govern the adhesion of ultra-thin 2D MoS₂. Our pioneering in situ experiments, utilizing TEM-based nanoindentation, provided precise imaging and force monitoring of MoS₂'s interaction with a diamond. We employed four MoS₂-coated AFM tips with varying radii and preparation methods, with films prepared on two Si wafers subjected to different oxidation protocols. Our findings, validated by Raman and X-ray photoelectron spectroscopy, reveal unique insights into MoS₂'s interfacial behavior. We observed a decreased structural order in MoS₂ on sharper tips, particularly those without pre-deposition oxidation. These results underscore the importance of residual stress between the MoS₂ film and substrate and the influence of curvature-induced residual stress in fostering less-ordered MoS₂ structures with heightened work of adhesion. Importantly, this is the first study to report the work of adhesion for MoS₂-diamond contact. Our findings highlight the crucial role of covalent bonding at contact points in the material transfer processes involving 2D materials. This is a critical insight for developing precise and reliable methods for manipulating 2D materials, which could significantly advance our understanding and application of materials science, particularly in nanotechnology and device fabrication.