†Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
‡NTT Basic Research Laboratories, NTT Corporation, Atsugi, Kanagawa 243-0198, Japan.
ACS Nano. 2015 Apr 28;9(4):4056-63. doi: 10.1021/acsnano.5b00103. Epub 2015 Mar 30.
Atomic-layer transition metal dichalcogenides (TMDCs) have attracted appreciable interest due to their tunable band gap, spin-valley physics, and potential device applications. However, the quality of TMDC samples available still poses serious problems, such as inhomogeneous lattice strain, charge doping, and structural defects. Here, we report on the growth of high-quality, monolayer WS2 onto exfoliated graphite by high-temperature chemical vapor deposition (CVD). Monolayer-grown WS2 single crystals present a uniform, single excitonic photoluminescence peak with a Lorentzian profile and a very small full-width at half-maximum of 21 meV at room temperature and 8 meV at 79 K. Furthermore, in these samples, no additional peaks are observed for charged and/or bound excitons, even at low temperature. These optical responses are completely different from the results of previously reported TMDCs obtained by mechanical exfoliation and CVD. Our findings indicate that the combination of high-temperature CVD with a cleaved graphite surface is an ideal condition for the growth of high-quality TMDCs, and such samples will be essential for revealing intrinsic physical properties and for future applications.
原子层过渡金属二卤族化合物（TMDCs）由于其可调带隙、自旋-谷物理和潜在的器件应用而引起了相当大的兴趣。然而，现有的 TMDC 样品的质量仍然存在严重的问题，例如不均匀的晶格应变、电荷掺杂和结构缺陷。在这里，我们报告了通过高温化学气相沉积（CVD）在剥离石墨上生长高质量的单层 WS2。单层生长的 WS2 单晶呈现出均匀的单激子光致发光峰，具有洛伦兹轮廓，在室温下半峰全宽非常小，为 21 毫电子伏特，在 79 K 下为 8 毫电子伏特。此外，在这些样品中，即使在低温下，也没有观察到带电和/或束缚激子的附加峰。这些光学响应与之前通过机械剥离和 CVD 获得的 TMDC 的报道结果完全不同。我们的发现表明，高温 CVD 与剥离石墨表面的结合是生长高质量 TMDC 的理想条件，这样的样品对于揭示本征物理性质和未来的应用将是必不可少的。
