Quality enhancement of low temperature metal organic chemical vapor deposited MoS₂: An experimental and computational investigation

Electronic quality of chemical vapor deposited MoS₂ is a function of crystallinity, which tends to decline with decrease in deposition temperature. Conventional thermal annealing can improve the quality but requires very high temperatures. In this study, we investigate a novel low temperature (room temperature to 400 °C) annealing process that exploits the electron wind force during passage of current. Here, moderate current density gives rise to atomic scale mechanical force whenever the electrons encounter defects in the lattice or grain boundaries (GBs). After hypothesizing that this force can significantly enhance defect mobility without any temperature field, we demonstrate the process using in situ transmission electron microscope and molecular dynamics simulation. Monolayer metal organic chemical vapor deposited MoS₂ deposited at 400 °C was post processed at temperature as low as 20 °C. Experimental results show five times enhancement in electrical conductivity, which is supported by electron diffraction patterns indicating significant grain growth. Discrete spots in diffraction indicate evolution of high crystallinity even at room temperature. Our computational model shows the mechanisms behind healing lattice defects as well as reorienting the GBs. The enhancement in microstructure of the specimen is also reflected in mechanical properties simulations on pre- and post-annealed specimens.