Surface passivation of black phosphorus via van der Waals stacked PTCDA

Abstract

Two-dimensional (2D) black phosphorus (BP) has received great attention due to its anisotropic mechanical, optical and electronic properties. However, the air-instability of BP seriously limits its further applications. Various approaches have been explored to improve the device stability of BP, including the encapsulation by inert 2D counterparts, and surface passivation by AlOxvia atomic layer deposition and by organic layers either van der Waals stacked or covalently bonded onto the surface. Here we systematically investigate the surface passivation effect of perylenetetracarboxylic dianhydride (PTCDA) on BP through a variety of in-situ characterization techniques. PTCDA molecule on BP adopts a lying down configuration with the molecular π-plane almost parallel to the BP surface, arising from the formation of multiple intermolecular hydrogen bonds. The evaporation of PTCDA on BP does not modify the intrinsic structure and electrical transport property of BP, as revealed by in-situ ultraviolet photoelectron spectroscopy (UPS)/x-ray photoelectron spectroscopy (XPS), and further corroborated by in-situ field-effect-transistor (FET) evaluation. After the air-exposure of PTCDA covered BP in dark, no obvious degradation on BP was observed by XPS. However, the electron mobility of the passivated BP FET significantly decreased by 80% after 20 h exposure despite lifetime of the passivated device was prolonged.