Realizing Long-Term Stability and Thickness Control of Black Phosphorus by Ambient Thermal Treatment

Few-layer black phosphorus (BP) has shown great potential for next-generation electronics with tunable band gap and high carrier mobility. For the electronic applications, the thickness modulation of a BP flake is essential due to its thickness-dependent electronic properties. However, controlling the precise thickness of few-layer BP is a challenge for the high-performance device applications. In this study, we demonstrate that thermal treatment under ambient condition precisely controls the thickness of BP flake. The thermal etching method utilizes the chemical reactivity of BP surface with oxygen and water molecules by the repeated formation and evaporation of phosphoric acid during thermal annealing. Field-effect transistor of the thickness-modulated BP sheet by thermal etching method shows a high hole mobility of ∼576 cm² V^-1 s^-1 and a high on-off ratio of ∼10⁵. The stability of the BP devices remained for 1 month under ambient condition without an additional protecting layer, resulting from the preservation of active BP layers below native surface phosphorus oxide.