High temperature oxidation of monolayer MoS2 and its effect on mechanical properties: A ReaxFF molecular dynamics study
Md. Habibur Rahman, Emdadul Haque Chowdhury, Sungwook Hong
Abstract
Molybdenum disulfide (MoS2) has lately been at the epicenter of scientific research due to its mesmerizing electronic, thermal, and physical properties, which have opened the door to a cornucopia of applications, including an efficient electrocatalyst, solid lubricant in satellites, and advanced electronics. Unfortunately, unavoidable high-temperature exposure to terrestrial environments can results in the oxidation of MoS2, thus deteriorating its surface chemistry and mechanical stability. For this reason, a fundamental understanding of the high-temperature oxidation mechanism of MoS2 and its mechanical stability is vitally important for real-world applications. Here, we used reactive molecular dynamics (RMD) simulations based on ReaxFF, one of the most effective computational methodologies, to investigate the atomic level high-temperature oxidation process on the basal surface of MoS2 and its impact on mechanical properties and fracture mechanics for the first time. First, we thoroughly studied the oxidation kinetics of MoS2 at 1400 K, 1500 K, and 1800 K temperatures. We revealed that MoS2 readily reacts with O2 above 1500 K. Oxidation started by the adsorption of O2 on the top of S atoms and culminated in the formation of oxy-sulfide (MoS2-xOx) solid solution. Tensile simulation results unveiled that oxidation notably degrades the mechanical properties of MoS2, such as fracture strength, fracture strain, Young's modulus, and fracture toughness. Interestingly, both pristine and oxidized MoS2 experienced a phase transition from trigonal prismatic (2H-MoS2) to metallic distorted octahedral (1T-MoS2) phase. Finally, we disclosed the fracture process of pristine and oxidized MoS2 samples from atomic trajectories. This study would lay the cornerstone for successfully realizing MoS2 in high-temperature functional systems as well as serving as a solid roadmap for engineering its chemical and mechanical properties.