van der Waals Epitaxial Growth and Interfacial Passivation of Two-Dimensional Single -Crystalline Few -Layer Gray Arsenic Nanoflakes

Numerous theoretical simulation works have predicted the fantastic properties of arsenene, such as a tunable band gap, topological states, and a high carrier mobility. However, the experimental synthesis of twodimensional arsenic materials is still difficult. Herein, we report the epitaxial growth of single-crystalline few-layer gray arsenic nanoflakes with hexagonal and half-hexagonal shapes via a van der Waals epitaxy method. The gray arsenic nanoflakes can be transferred from mica to other substrates without structural damage. Moreover, a universal method for estimating the antidegradation efficiency of polymer-passivated gray arsenic nanoflakes by determining the interfacial interaction energies and geometry changes via first-principles calculations was developed. Consistent with theoretical predictions, we further experimentally confirm that functional polymer coating can effectively suppress the chemical degradation and phase transformation of gray arsenic nanoflakes for at least 50 days under ambient exposure, thus facilitating further nanodevice fabrication, preservation, and measurements. Moreover, the gray arsenic nanoflakes show metal to semiconductor transformation after long-term ambient exposure owing to the oxidation of arsenic in air.