中文摘要：

单层二硫化钼是继石墨烯后的一种新型二维材料.它是一种直接带隙半导体,具有优异的光电特性,从而受到人们的广泛关注.之前的研究报道过单层二硫化钼在氩气中退火后可以提升其A激子峰的荧光强度,但我们发现,空气中退火较氩气退火效果更为明显.本文重点研究了在空气中退火对二硫化钼的荧光特性的影响.不同条件下制备的单层二硫化钼样品,经过在空气中退火处理后,荧光峰位均发生了蓝移,荧光强度提升了一个数量级.我们认为,这是由于空气退火造成二硫化钼缺陷的形成,大量氧气分子被缺陷束缚并发生电荷转移.氧气分子充当受主的角色,起着P型掺杂的作用.电荷的抽取造成二硫化钼的负电激子减少,中性激子增多,提升了其荧光量子效率.我们在对照实验中发现,NH3吸附在二硫化钼表面时,荧光强度下降,峰位红移,这是由于NH3分子充当施主的角色,造成负电激子增多,中性激子减少.本文为提高单层二硫化钼的荧光量子效率提供了一种简单有效的方法.

英文摘要：

Monolayer molybdenum disulfide is a novel two-dimensional material beyond graphene. It is a direct band gap semiconductor with excellent electrical and optical properties, promising wide application in nanoelectronics and optoelectronics, thus has drawn much attention recently. In this paper, we investigate the enhancement of photoluminescence of monolayer molybdenum disulfide by annealing in air. Monolayer molybdenum disulfide samples were prepared by mechanical exfoliation and chemical vapor deposition with molybdenum oxide and sulfur as sources, and argon as carrier gas. We found that air annealing for several minutes can distinctly enhance the photoluminescence intensity of A exciton by an order of magnitude, which is much better than annealing in argon. The blue shift of A exciton peak is observed after air annealing for all the monolayer molybdenum disulfide samples prepared by different methods above. We also found that this phenomenon widely exists in samples with different substrates like silicon dioxide and sapphire. Electrical transport measurements were carried out and indicate that the carrier mobility of monolayer molybdenum disulfide is largely reduced after annealing in air, which might mean the formation of considerable defects. This phenomenon is believed to be due to the doping effect caused by adsorption of oxygen, which is bonded to the defects after annealing. As acceptors, these oxygen dopants change the distribution of trions and neutral excitons, resulting in less tritons but more neutral excitons. Neutral excitons yield much higher quantum efficiency. As a comparison, we carried out control experiments in which annealing was in NH3 atmosphere. We found that photoluminescence is red shifted and can be quenched. This research results give a simple and effective method to enhance the photoluminescence of monolayer molybdenum disulfide.