Xiao-Fen Qiao,†,¶ Jiang-Bin Wu,†,¶ Lin-Wei Zhou,‡,¶ Jing-Si Qiao,‡ Wei Shi,† Tao Chen,† Xin Zhang,† Jun Zhang,† Wei Ji,∗,‡ and Ping-Heng Tan∗,†
Xiao-Fen Qiao,†,¶ Jiang-Bin Wu,†,¶ Lin-Wei Zhou,‡,¶ Jing-Si Qiao,‡ Wei Shi,† Tao Chen,† Xin Zhang,† Jun Zhang,† Wei Ji,∗,‡ and Ping-Heng Tan∗,† State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China, and Department of Physics, Renmin University of China, Beijing 100872, China E-mail: firstname.lastname@example.org; email@example.com
DOI:10.1039/C6NR01569G Publication Date: March 16, 2016
The anisotropic two-dimensional (2D) van der Waals (vdW) layered materials, with both scientiﬁc interest and potential application, have one more dimension to tune the properties than the isotropic 2D materials. The interlayer vdW coupling determines the properties of 2D multi-layer materials by varying stacking orders. As an important representative anisotropic 2D materials, multilayer rhenium disulﬁde (ReS2) was expected to be random stacking and lack of interlayer coupling. Here, we demonstrate two stable stacking orders (aa and ¯ab) of N layer (NL, N>1) ReS2 from ultralow-frequency and high-frequency Raman spectroscopy, pho toluminescence spectroscopy and ﬁrst-principles density functional theory calculation. Two interlayer shear modes are observed in aa-stacked NL-ReS2 while only one interlayer shear mode appears in ¯ab-stacked NL-ReS2, suggesting anisotropic-like and isotropic-like stacking orders in aa- and ¯ab-stacked NL-ReS2, respectively. The frequency of the interlayer shear and breathing modes reveals unexpected strong interlayer coupling in aa- and ¯ab-NL-ReS2, the force constants of which are 55-90% to those of multilayer MoS2. The observation of strong interlayer coupling and polytypism in multi-layer ReS2 stimulate future studies on the structure, electronic and optical properties of other 2D anisotropic materials.