Achieving Ambient Stability of Borophene via Ultrahigh Vacuum Alumina Encapsulation
Eden Aklile, Xiaolong Liu, Dominic P. Goronzy, Matthew S. Rahn, Qiucheng Li, Cataldo Lamarca, Mark C. Hersam
Abstract
In recent years, a range of two-dimensional boron polymorphs, collectively referred to as borophene, have been experimentally realized on a diverse set of metallic substrates by bottom-up synthesis in ultrahigh vacuum (UHV). However, since borophene is highly reactive chemically and rapidly oxidizes in ambient conditions, robust encapsulation methods are needed to ensure the long-term stability of borophene outside of UHV environments. Here, we demonstrate that encapsulation using UHV electron-beam evaporation of alumina (AlO x ) prevents oxidation of borophene in ambient conditions. This protection of borophene from chemical degradation is achieved with UHV-deposited AlO x encapsulated layers as thin as 3.7 nm. X-ray photoelectron spectroscopy and scanning probe microscopy confirm that this encapsulation scheme preserves the integrity of borophene for at least 12 months in ambient conditions. This long-term stability addresses a critical hurdle in the processing and integration of borophene into practical device architectures.