Thermal Sublimation: a Scalable and Controllable Thinning Method for the   Fabrication of Few-Layer Black Phosphorus
  In this work, we reported uniform layer-by-layer sublimation of black phosphorus under heating below 600 K. The uniformity and crystallinity of BP samples after thermal thinning were confirmed by Raman spectra and 2D Raman imaging. A uniform and crystalline bilayer black phosphorus flake with an area of 180 um^2 was prepared with this method. No micron scale defects were observed. The sublimation rate of BP was around 0.18 nm / min at 500 K and 1.5 nm / min at 550 K. Both room and high temperature Raman peak intensity ratio Si/A2g vs. BP thickness relations were established for in-situ thickness determination. The sublimation thinning method was shown to be a controllable and scalable approach to prepare few-layer black phosphorus. 
Weijun Luo, Rui Yang, Jialun Liu, Yunlong Zhao, Wenjuan Zhu, Guangrui   (Maggie) Xia
cond-mat.mtrl-sci