The effect of room temperature ultraviolet-ozone (UV-O3) exposure of MoS2 on the uniformity of subsequent atomic layer deposition of Al2O3 is investigated. It is found that a UV-O3 pre-treatment removes adsorbed carbon contamination from the MoS2 surface and also functionalizes the MoS2 surface through the formation of a weak sulfur-oxygen bond without any evidence of molybdenum-sulfur bond disruption. This is supported by first principles density functional theory calculations which show that oxygen bonded to a surface sulfur atom while the sulfur is simultaneously back-bonded to three molybdenum atoms is a thermodynamically favorable configuration. The adsorbed oxygen increases the reactivity of MoS2 surface and provides nucleation sites for atomic layer deposition of Al2O3. The enhanced nucleation is found to be dependent on the thin film deposition temperature.
Angelica Azcatl, Stephen McDonnell, Santosh KC, Xin Peng, Hong Dong, Xiaoye Qin, Rafik Addou, Greg Mordi, Ning Lu, Jiyoung Kim, Moon Kim, Kyeongjae Cho, and Robert Wallace. "MoS2 functionalization for ultra-thin atomic layer deposited dielectrics" Applied Physics Letters (2014). doi:10.1063/1.4869149