Physical adsorption and oxidation of ultra-thin MoS<sub>2</sub> crystals: insights into surface engineering for 2D electronics and beyond
Yingchun Jiang, Zihan Liu, Huimin Zhou, Anju Sharma, Jia Deng, Changhong Ke
Abstract
Abstract The oxidation mechanism of atomically thin molybdenum disulfide (MoS 2 ) plays a critical role in its nanoelectronics, optoelectronics, and catalytic applications, where devices often operate in an elevated thermal environment. In this study, we systematically investigate the oxidation of mono- and few-layer MoS 2 flakes in the air at temperatures ranging from 23 °C to 525 °C and relative humidities of 10%–60% by using atomic force microscopy (AFM), Raman spectroscopy and x-ray photoelectron spectroscopy. Our study reveals the formation of a uniform nanometer-thick physical adsorption layer on the surface of MoS 2 , which is attributed to the adsorption of ambient moisture. This physical adsorption layer acts as a thermal shield of the underlying MoS 2 lattice to enhance its thermal stability and can be effectively removed by an AFM tip scanning in contact mode or annealing at 400 °C. Our study shows that high-temperature thermal annealing and AFM tip-based cleaning result in chemical adsorption on sulfur vacancies in MoS 2 , leading to p-type doping. Our study highlights the importance of humidity control in ensuring reliable and optimal performance for MoS 2 -based electronic and electrochemical devices and provides crucial insights into the surface engineering of MoS 2 , which are relevant to the study of other two-dimensional transition metal dichalcogenide materials and their applications.