Thermal investigation of Pd interface with molybdenum disulfide

Abstract

The thermal stability of molybdenum disulfide (MoS2) films, and particularly of the 1T-MoS2 metallic phase, plays a crucial role in their applicability across diverse technological fields. In this research, we successfully achieved a phase transition of multilayer MoS2 nanosheets from the semiconducting 2H phase to the metallic 1T phase through Pd substitution of Mo atoms on non-stoichiometric (sulfur-rich) MoS2 substrates and MoS2 hybrids with reduced graphene oxide (MoS2-rGO). This investigation involved studying the thermal stability of MoS2 thin films with mixed 1T-2H phases, up to 500 °C, in an ultra-high vacuum (UHV) environment. Our findings indicate that the 1T phase transforms to the 2H semiconducting stable phase at different temperatures, depending on the surface chemistry. In sulfur-rich substrates, the 1T phase remains present up to approximately 400 °C, while it vanishes on the stoichiometric MoS2-rGO films. Notably, enhanced thermal stability of the 1T phase is achieved with a sulfur surplus, regardless of the presence of rGO. Furthermore, during annealing, we observed Pd sintering, accompanied by a chemical state change from metallic Pd0 to Pd2+. These results elucidate the stability of 1T-MoS2 within an acceptable temperature range for the catalytic process and energy applications involving MoS2.