In Situ Thermal Decomposition of Exfoliated Two-Dimensional Black Phosphorus

TL;DR

This study investigates the thermal decomposition of exfoliated 2D black phosphorus using in situ microscopy and spectroscopy, revealing decomposition at ~400°C and detailing the process from crack formation to amorphous phosphorus residue.

Contribution

It provides the first atomic-scale in situ analysis of 2D black phosphorus thermal degradation, highlighting differences from bulk BP and elucidating the decomposition mechanism.

Findings

Decomposition occurs at ~400°C in vacuum.

Cracks initiate along the [001] direction.

Residual structure is an amorphous phosphorus skeleton.

Abstract

With a semiconducting band gap and high charge carrier mobility, two-dimensional (2D) black phosphorus (BP), often referred to as phosphorene, holds significant promise for next generation electronics and optoelectronics. However, as a 2D material, it possesses a higher surface area to volume ratio than bulk BP, suggesting that its chemical and thermal stability will be modified. Herein, an atomic-scale microscopic and spectroscopic study is performed to characterize the thermal degradation of mechanically exfoliated 2D BP. From in situ scanning/transmission electron microscopy, decomposition of 2D BP is observed to occur at ~400 {\deg}C in vacuum, in contrast to the 550 {\deg}C bulk BP sublimation temperature. This decomposition initiates via eye-shaped cracks along the [001] direction and then continues until only a thin, amorphous red phosphorous like skeleton remains. In situ electron energy loss spectroscopy, energy-dispersive X-ray spectroscopy, and energy-loss near-edge structure changes provide quantitative insight into this chemical transformation process.