Ripples and Layers in Ultrathin MoS2 Membranes
Ripples and Layers in Ultrathin MoS2 Membranes
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DOI：
10.1021/nl2022288
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发表时间：
2011-12-01
期刊：
影响因子：
10.8
通讯作者：
Kis, Andras
中科院分区：
文献类型：
--
作者：
Brivio, Jacopo;Alexander, Duncan T. L.;Kis, Andras
单层二硫化钼（MoS2）是一种新兴的二维半导体，在纳米电子和能量收集领域具有潜在的广泛应用。事实上，MoS2 可以剥离至单层厚度，这使得 MoS2 在实际应用和基础研究中都很有趣，其中超薄 MoS2 的结构和晶序将对电子、机械和其他性能产生强烈影响。在这里，我们报告了悬浮单层和少层 MoS2 膜的透射电子显微镜研究，其厚度先前使用光学识别和原子力显微镜确定。电子显微镜显示，单层 MoS2 显示出长程晶体有序性，尽管观察到表面粗糙度可达 1 nm 高度的波纹，就像石墨烯的情况一样，这意味着类似的机制导致了两种二维材料的稳定性。观察到的波纹可以解释由于剥落而导致的 MoS2 迁移率的降低。我们还发现，由于层数减少而导致的对称性破缺导致单层和多层 MoS2 的电子束衍射图案具有独特的特征，这可以用作仅使用电子显微镜识别单层的方法。悬浮单层 MoS2 膜的隔离将提高我们对二维系统、其稳定性以及其结构、形态以及电气和机械性能之间相互作用的理解。
Single-layer molybdenum disulfide (MoS2) is a newly emerging two-dimensional semiconductor with a potentially wide range of applications in the fields of nanoelectronics and energy harvesting. The fact that it can be exfoliated down to single-layer thickness makes MoS2 interesting both for practical applications and for fundamental research, where the structure and crystalline order of ultrathin MoS2 will have a strong influence on electronic, mechanical, and other properties. Here, we report on the transmission electron microscopy study of suspended single- and few-layer MoS2 membranes with thicknesses previously determined using both optical identification and atomic force microscopy. Electron microscopy shows that monolayer MoS2 displays long-range crystalline order, although surface roughening has been observed with ripples which can reach 1 nm in height, just as in the case of graphene, implying that similar mechanisms are responsible for the stability of both two-dimensional materials. The observed ripples could explain the degradation of mobility in MoS2 due to exfoliation. We also find that symmetry breaking due to the reduction of the number of layers results in distinctive features in electron-beam diffraction patterns of single- and multilayer MoS2, which could be used as a method for identifying single layers using only electron microscopy. The isolation of suspended single-layer MoS2 membranes will improve our understanding of two-dimensional systems, their stability, and the interplay between their structures, morphologies, and electrical and mechanical properties.