Thermal sublimation: a scalable and controllable thinning method for the fabrication of few-layer black phosphorus.

We report 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 Raman mapping. The sublimation rate of BP was around 0.18 nm min(-1) at 500 K and 1.15 nm min-1 at 550 K. Both room and high temperature Raman peak intensity ratio Si/A(g)(2) as functions of BP thickness were established for in situ thickness determination and control. Uniform and crystalline 2 to 4-layer BP flakes with areas from 10 to 1000 mu m(2) were prepared with this method. No micron scale defects were observed. The sublimation thinning method was shown to be a controllable and scalable approach to prepare high-quality few-layer black phosphorus.