Resolving and Tuning Mechanical Anisotropy in Black Phosphorus via   Nanomechanical Multimode Resonance Spectromicroscopy
  Black phosphorus (P) has emerged as a layered semiconductor with a unique crystal structure featuring corrugated atomic layers and strong in-plane anisotropy in its physical properties. Here, we demonstrate that the crystal orientation and mechanical anisotropy in free-standing black P thin layers can be precisely determined by spatially resolved multimode nanomechanical resonances. This offers a new means for resolving important crystal orientation and anisotropy in black P device platforms in situ beyond conventional optical and electrical calibration techniques. Furthermore, we show that electrostatic-gating-induced straining can continuously tune the mechanical anisotropic effects on multimode resonances in black P electromechanical devices. Combined with finite element modeling (FEM), we also determine the Young's moduli of multilayer black P to be 116.1 and 46.5 GPa in the zigzag and armchair directions, respectively. 
Zenghui Wang, Hao Jia, Xu-Qian Zheng, Rui Yang, G. J. Ye, X. H. Chen,   Philip X.-L. Feng
cond-mat.mes-hall