  Two-dimensional (2D) materials have aroused considerable research interests
owing to their potential applications in nanoelectronics and optoelectronics.
Thermodynamic stability of 2D structures inevitably affects the performance and
power consumption of the fabricated nanodevices. Black arsenic (b-As), as a
cousin of black phosphorus, has presented the extremely high anisotropy in
physical properties. However, the systematic research on structural stability
of b-As is still lack. Herein, we demonstrated the detailed analysis on
structural metastability of the natural b-As, and determined its existence
conditions in terms of two essential thermodynamic variables as hydrostatic
pressure and temperature. Our results confirmed that b-As can only survive
below 0.7 GPa, and then irreversibly transform to gray arsenic, in consistent
with our theoretical calculations. Furthermore, thermal annealing strategy was
developed to precisely control the thickness of b-As flake, and it sublimates
at 300 oC. These results could pave the way for 2D b-As in many promising
applications.
