Defect engineering for thermal transport properties of nanocrystalline molybdenum diselenide

Molybdenum diselenide (MoSe₂) is attracting great attention as a transition metal dichalcogenide (TMDC) due to its unique applications in micro-electronics and beyond. In this study, the role of defects in the thermal transport properties of single-layer MoSe₂ is investigated using non-equilibrium molecular dynamics (NEMD) simulations. Specifically, this work quantifies how different microstructural defects such as vacancies and grain boundaries (GBs) and their concentration (N) alter the thermal conductivity (TC) of single crystal and nanocrystalline MoSe₂. These results show a significant drop in thermal conductivity as the concentration of defects increases. Specifically, point defects lower the TC of MoSe₂ in the form of N^- where β is 0.5, 0.48 and 0.36 for V_Mo, V_Mo-Se and V_Se vacancies, respectively. This study also examines the impact of grain boundaries on the thermal conductivity of nanocrystalline MoSe₂. These results suggest that GB migration and stress-assisted twinning along with localized phase transformation (2H to 1T) are the primary factors affecting the thermal conductivity of nanocrystalline MoSe₂. Based on MD simulations, TC of polycrystalline MoSe₂ increases with the average grain size (d̄) in the form of d̄^4.5. For example, the TC of nanocrystalline MoSe₂ with d̄ = 11 nm is around 40% lower than the TC of the pristine monocrystalline sample with the same dimensions. Finally, the influence of sample size and temperature is studied to determine the sensitivity of quantitative thermal properties to the length scale and phonon scattering, respectively. The results of this work could provide valuable insights into the role of defects in engineering the thermal properties of next generation semiconductor-based devices.