1 State Key Laboratory of Silicon Materials, Key Laboratory of Advanced Materials and Applications for Batteries of Zhejiang Province, Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China 2 Department of Physics, Southeast University, Nanjing 211189, China 3 Graphene Research and Characterization Center, Taizhou Sunano New Energy Co., Ltd. Taizhou 225300, China These authors contributed equally to this work.
There have been continuous efforts to seek 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 a
subsequent Ar+ plasma thinning process. The thickness of phosphorene is
unambiguously determined by optical contrast spectra combined with atomic
force microscopy (AFM). Raman spectroscopy is used to characterize the pristine
and plasma-treated samples. The Raman frequency of the A2g mode stiffens,
and the intensity ratio of A2g to A1g modes shows a monotonic discrete increase
with the decrease of phosphorene thickness down to a monolayer. All those
phenomena can be used to identify the thickness of this novel two-dimensional
semiconductor. This work on monolayer phosphorene fabrication and thickness
determination will facilitate future research on phosphorene.