Feng Yulin, Zhang Kailiang, Li Hui, Wang Fang, Zhou Baozeng, Fang Mingxu, Wang Weichao, Wei Jun, Wong H S Philip
School of Electrical and Electronic Engineering, Tianjin Key Laboratory of Film Electronic & Communication Devices, Tianjin University of Technology, Tianjin, 300384, People's Republic of China.
Nanotechnology. 2017 Jun 30;28(29):295705. doi: 10.1088/1361-6528/aa7183.
The surface potential (SP) variations in mono and multilayer molybdenum disulfide (MoS) are visualized in situ and detected using Kelvin probe force microscopy (KPFM) in different humidity conditions for the first time. N-type doping, which originates from the SiO substrate, is discovered in the exfoliated MoS and is accompanied by a screening length of five layers. The influence of water, which serves as an environmental gating for MoS, is investigated by controlling the relative humidities (RHs) in the environmental chamber. A monotonic decrease in the SP is observed when the threshold concentration is achieved. This corresponds to the Fermi level variation, which is dominated by different processes. The results also indicate that water adsorption could result in MoS p-type doping and provide compensation that partially counteracts the substrate effect. Under this condition, the interlayer screening effect is influenced because of the water dipole-induced electric field. Density functional theory calculations are performed to determine the band structure variations and the interactions between water molecules and between water molecules and the MoS surface in mono and trilayer MoS under different RHs. The calculations are in excellent agreement with the experimental results. We propose that in situ measurements of the SP using KPFM under different environmental regimes is a noninvasive and effective method to provide real-time visualization and detection of electronic property variations in two-dimensional materials.
首次在不同湿度条件下，使用开尔文探针力显微镜（KPFM）对单层和多层二硫化钼（MoS）中的表面电位（SP）变化进行了原位可视化和检测。在剥离的MoS中发现了源自SiO衬底的N型掺杂，并伴随着五层的屏蔽长度。通过控制环境腔室中的相对湿度（RHs），研究了作为MoS环境门控的水的影响。当达到阈值浓度时，观察到SP单调下降。这对应于费米能级变化，其由不同过程主导。结果还表明，水吸附可导致MoS p型掺杂，并提供补偿，部分抵消衬底效应。在此条件下，由于水偶极子诱导的电场，层间屏蔽效应受到影响。进行了密度泛函理论计算，以确定不同RHs下单层和三层MoS中能带结构的变化以及水分子之间以及水分子与MoS表面之间的相互作用。计算结果与实验结果非常吻合。我们提出，在不同环境条件下使用KPFM对SP进行原位测量是一种无创且有效的方法，可实时可视化和检测二维材料中的电子性质变化。
