The Influence of Atomic-Scale Defects on Thermal Transport in MoS₂

Transition-metal dichalcogenides, such as molybdenum disulfide (MoS₂), have attracted considerable attention as tunable band-gap semiconductors that may be fabricated in a monolayer format and that give rise to unique electrical and thermal properties. These physical properties are directly linked to the layer structure, which is sensitive to defects and impurities. While several computational studies have investigated the thermal conductivity of supported and encapsulated MoS₂, the impact of lattice defects on the thermal conductivity of MoS₂ and the thermal boundary conductance between MoS₂ and its support substrate has not been studied experimentally as a function of both defect density and layer number. In this work, we use frequency domain thermal reflectance to study the thermal transport properties of mechanically exfoliated MoS₂ flakes with controlled defect densities and a known number of layers, which are supported on sapphire substrates. The sulfur defect density is controlled via hydrogen-based plasma, and x-ray photoelectron spectroscopy is used to characterize the density of these sulfur vacancy defects. In combination with our materials characterization, we provide an effective thermal conductance analysis to explain the reduction in thermal transport due to carrier scattering by vacancies. The results from this study serve to further enhance our understanding of the fundamental physics of phonon transport in the presence of defects and provide a pathway for studying thermal transport in nanoscale electronic devices based upon 2D materials.