Photoluminescence Lightening: Extraordinary Oxygen Modulated Dynamics in WS2 Monolayers

Transition metal dichalcogenide monolayers exhibit ultrahigh surface sensitivity since they expose all atoms to the surface and thereby influence their optoelectronic properties. Here, we report an intriguing lightening of the photoluminescence (PL) from the edge to the interior over time in the WS2 monolayers grown by physical vapor deposition method, with the whole monolayer brightened eventually. Comprehensive optical studies reveal that the PL enhancement arises from the p doping induced by oxygen adsorption. First-principles calculations unveil that the dissociation of chemisorbed oxygen molecule plays a significant role; i.e., the dissociation at one site can largely promote the dissociation at a nearby site, facilitating the photoluminescence lightening. In addition, we further manipulate such PL brightening rate by controlling the oxygen concentration and the temperature. The presented results uncover the extraordinary surface chemistry and related mechanism in WS2 monolayers, which deepens our insight into their unique PL evolution behavior.

过渡金属二硫化物单分子层具有超高的表面敏感性，因为它们将所有原子都暴露在表面，从而影响其光电性能。在此，我们报道了通过物理气相沉积法生长的WS₂单分子层中，随着时间的推移，从边缘到内部的光致发光（PL）出现了有趣的增强现象，最终整个单分子层都变亮了。综合光学研究表明，PL增强是由氧吸附引起的p型掺杂导致的。第一性原理计算揭示了化学吸附氧分子的解离起着重要作用；即一个位点的解离能在很大程度上促进附近位点的解离，从而促进光致发光增强。此外，我们通过控制氧浓度和温度进一步调控了这种PL增强速率。所呈现的结果揭示了WS₂单分子层中非凡的表面化学性质及相关机制，这加深了我们对其独特的PL演化行为的理解。