Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, 10607, Taiwan.
Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei, 10607, Taiwan.
Nat Commun. 2018 Apr 12;9(1):1442. doi: 10.1038/s41467-018-03824-6.
Because the surface-to-volume ratio of quasi-two-dimensional materials is extremely high, understanding their surface characteristics is crucial for practically controlling their intrinsic properties and fabricating p-type and n-type layered semiconductors. Van der Waals crystals are expected to have an inert surface because of the absence of dangling bonds. However, here we show that the surface of high-quality synthesized molybdenum disulfide (MoS) is a major n-doping source. The surface electron concentration of MoS is nearly four orders of magnitude higher than that of its inner bulk. Substantial thickness-dependent conductivity in MoS nanoflakes was observed. The transfer length method suggested the current transport in MoS following a two-dimensional behavior rather than the conventional three-dimensional mode. Scanning tunneling microscopy and angle-resolved photoemission spectroscopy measurements confirmed the presence of surface electron accumulation in this layered material. Notably, the in situ-cleaved surface exhibited a nearly intrinsic state without electron accumulation.
由于准二维材料的比表面积极高，因此了解其表面特性对于实际控制其本征性能和制备 p 型和 n 型层状半导体至关重要。由于不存在悬空键，范德华晶体预计具有惰性表面。然而，在这里我们表明，高质量合成的二硫化钼 (MoS) 的表面是主要的 n 型掺杂源。MoS 的表面电子浓度比其内部体相高近四个数量级。在 MoS 纳米片中观察到显著的厚度依赖性电导率。传输长度法表明，MoS 中的电流输运遵循二维行为，而不是传统的三维模式。扫描隧道显微镜和角度分辨光发射谱测量证实了这种层状材料中表面电子积累的存在。值得注意的是，原位剥离的表面表现出几乎没有电子积累的本征状态。
