Investigating Local Electron Transport Dynamics in Layer-Dependent MoS₂/RGO Heterostructures Using Conductive Atomic Force Microscopy

Layer-dependent physical properties of exfoliated 2D materials are critical for both fundamental studies and technological applications. However, our understanding of local electrical conductivity on an atomic scale remains limited. In this study, we employ polydimethylsiloxane (PDMS)-assisted mechanical exfoliation followed by a micromanipulation technique to achieve a large-sized monolayer MoS₂ (∼30 μm) for investigating its layer-dependent physical properties. Raman spectroscopy revealed the distinct structure of monolayer MoS₂, with increased peak intensity and a narrower separation between the A_1g and E_2g peaks. Photoluminescence (PL) spectra showed increased intensity and higher photon energy levels in monolayer MoS₂ compared to bilayer and multilayer MoS₂. Raman and PL mapping of monolayer and bilayer MoS₂ provides valuable insights into their structural and optical characteristics. Atomic force microscopy (AFM) measurements indicated thicknesses of approximately 0.7 nm for monolayer MoS₂ and 0.4 nm for reduced graphene oxide (RGO). Kelvin probe force microscopy revealed a contact potential difference between the monolayer and few-layer MoS₂ and the MoS₂/RGO surface. Conductive AFM (CAFM) measurements demonstrated consistent and reproducible electrical characteristics of the monolayer MoS₂/RGO surface. Moreover, the obtained work function (WF) and Schottky barrier height (Φ_B) of MoS₂/RGO exhibited layer-dependent behavior: increasing layer thickness reduced the Φ_B due to enhanced charge transfer while raising the WF, indicating shifts in Fermi level alignment and the interfacial electronic structure. These findings offer a deeper understanding of the optical, structural, and electrical properties of the MoS₂/RGO heterostructures.