Yanyong Li,1 Zhixin Hu,2 Shenghuang Lin,1 Sin Ki Lai,1 Wei Ji,2 and Shu Ping Lau1,
1Department of Applied Physics, the Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China
2Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials & Micro-Nano Devices, Renmin University of China, Beijing 100872, China
DOI:10.1002/adfm.201600986 Publication Date: June 22, 2016
Herein we report the giant anisotropic strain response in vibrational modes of ultrathin black phosphorus (BP). A modified bending technique was employed to apply precise uniaxial tensile strain along the zigzag or armchair directions of the ultrathin BP flakes. The Raman shift rates of the, and modes of the ultrathin BP are significantly distinct for strain applied along the zigzag or armchair direction. For the applied strain along the zigzag direction, the Raman shift rate and the Grüneisen parameterof the mode can reach a remarkable value of ~ -11 cm-1/% strain and~ 2.5 respectively, which are the largest among all the reported values in common two-dimensional materials. Density functional theory calculations were performed to understand the exceptional anisotropic strain response of the vibrational modes in the ultrathin BP. It is found that not only the bond lengths but also the bond angels are changed in the ultrathin BP upon applied strain which lead to the giant anisotropic strain response in the mode. Furthermore, we demonstrate a simple method based entirely on the strained ultrathin BP and conventional Raman spectroscopy to determine the crystallographic orientations of ultrathin BP without the aid of polarized Raman spectroscopy. This work may pave a way to study the strain-induced anisotropic electrical conductance and the magnetotransport properties of BP.