Plasma-assisted fabrication of monolayer phosphorene and its Raman   characterization
  There have been continuous efforts to seek for novel functional two-dimensional semiconductors with high performance for future applications in nanoelectronics and optoelectronics. In this work, we introduce a successful experimental approach to fabricate monolayer phosphorene by mechanical cleavage and the following Ar+ plasma thinning process. The thickness of phosphorene is unambiguously determined by optical contrast combined with atomic force microscope (AFM). Raman spectroscopy is used to characterize the pristine and plasma-treated samples. The Raman frequency of A2g mode stiffens, and the intensity ratio of A2g to A1g modes shows monotonic discrete increase with the decrease of phosphorene thickness down to monolayer. All those phenomena can be used to identify the thickness of this novel two-dimensional semiconductor efficiently. This work for monolayer phosphorene fabrication and thickness determination will facilitates the research of phosphorene. 
Wanglin Lu, Haiyan Nan, Jinhua Hong, Yuming Chen, Chen Zhu, Zheng   Liang, Xiangyang Ma, Zhenhua Ni, Chuanhong Jin, Ze Zhang
cond-mat.mtrl-sci