Qiao Xiao-Fen, Wu Jiang-Bin, Zhou Linwei, Qiao Jingsi, Shi Wei, Chen Tao, Zhang Xin, Zhang Jun, Ji Wei, Tan Ping-Heng
State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China.
Department of Physics, Renmin University of China, Beijing 100872, China.
Nanoscale. 2016 Apr 21;8(15):8324-32. doi: 10.1039/c6nr01569g.
Anisotropic two-dimensional (2D) van der Waals (vdW) layered materials, with both scientific interest and application potential, offer one more dimension than isotropic 2D materials to tune their physical properties. Various physical properties of 2D multi-layer materials are modulated by varying their stacking orders owing to significant interlayer vdW coupling. Multilayer rhenium disulfide (ReS2), a representative anisotropic 2D material, was expected to be randomly stacked and lack interlayer coupling. Here, we demonstrate two stable stacking orders, namely isotropic-like (IS) and anisotropic-like (AI) N layer (NL, N > 1) ReS2 are revealed by ultralow- and high-frequency Raman spectroscopy, photoluminescence and first-principles density functional theory calculation. Two interlayer shear modes are observed in AI-NL-ReS2 while only one shear mode appears in IS-NL-ReS2, suggesting anisotropic- and isotropic-like stacking orders in IS- and AI-NL-ReS2, respectively. This explicit difference in the observed frequencies identifies an unexpected strong interlayer coupling in IS- and AI-NL-ReS2. Quantitatively, the force constants of them are found to be around 55-90% of those of multilayer MoS2. The revealed strong interlayer coupling and polytypism in multi-layer ReS2 may stimulate future studies on engineering physical properties of other anisotropic 2D materials by stacking orders.
各向异性二维（2D）范德华（vdW）层状材料兼具科学研究价值和应用潜力，与各向同性2D材料相比，它提供了一个额外的维度来调节其物理性质。由于显著的层间vdW耦合，二维多层材料的各种物理性质会因堆叠顺序的不同而受到调制。多层二硫化铼（ReS2）作为一种典型的各向异性二维材料，预计会随机堆叠且缺乏层间耦合。在此，我们通过超低频和高频拉曼光谱、光致发光以及第一性原理密度泛函理论计算，揭示了两种稳定的堆叠顺序，即类各向同性（IS）和类各向异性（AI）的N层（NL，N>1）ReS2。在AI-NL-ReS2中观察到两种层间剪切模式，而在IS-NL-ReS2中仅出现一种剪切模式，这分别表明IS-NL-ReS2和AI-NL-ReS2中存在类各向异性和类各向同性的堆叠顺序。观测频率上的这种明显差异表明，IS-NL-ReS2和AI-NL-ReS2中存在意想不到的强层间耦合。定量分析发现，它们的力常数约为多层MoS2的55-90%。多层ReS2中揭示的强层间耦合和多型性可能会激发未来通过堆叠顺序对其他各向异性二维材料的物理性质进行工程调控的研究。
