Ambient stability of graphene-borophene heterostructures
In a new paper published in Advanced Electronic Materials, our colleague Marin Petrović in collaboration with scientists from Elettra synchrotron, University of Trieste and University of Venice has demonstrated a new route for the synthesis of layered graphene-borophene heterostructures which exhibit exceptional chemical and mechanical stability in ambient conditions.
Coupling Borophene to Graphene in Air-Stable Heterostructures
Matteo Jugovac, Iulia Cojocariu, Carlo Alberto Brondin, Alessandro Crotti, Marin Petrović, Stefano Bonetti, Andrea Locatelli, Tevfik Onur Mentes,
Advanced Electronic Materials, 2300136 (2023).
A relatively new member of two-dimensional materials family and a close cousin of graphene – borophene – is an interesting material composed only of boron atoms and does not occur in nature, but can be synthesized in a laboratory. It is characterized by a thickness of only one atom and good mechanical, thermal and electronic properties, which make it interesting for various nanotechnological applications. However, one of the main shortfalls of borophene is pronounced chemical reactivity which limits its stability outside laboratory conditions as well as its integration into more complex systems and devices.
In this latest study, our colleague Petrović in cooperation with scientists from Elettra synchrotron and universities in Trieste and Venice present a novel method for the synthesis of heterostructures in which borophene has been obtained on a metal substrate (an iridium single-crystal) and is additionally covered by a single layer of graphene. The whole synthesis procedure took place in ultra-high vacuum conditions, where it was tracked via low-energy electron microscope (LEEM) (see Figure 1). Basic principle of the synthesis is high-temperature graphene growth on iridium which already contains significant amount of dissolved boron. During cooling, dissolved boron segregates to the iridium surface and self-assembles into borophene, i.e. borophene is formed between the graphene and the Ir substrate. Effectively, a vertical graphene-borophene heterostructure is formed.
Regions of the sample on which borophene has not been covered by graphene show substantial chemical reactivity even in ultra-high vacuum conditions (~10E-10 mbar), as can be read out from modifications of the B 1s and O 2s signals obtained via x-ray photoemission spectroscopy (XPS) (see Figure 2a, blue curves). In other words, borophene is contaminated by adsorption of various residual molecules from vacuum which significantly alters its good intrinsic properties. However, in regions of the sample which contain graphene-borophene heterostructure, i.e. on which borophene is protected by a graphene layer, borophene with preserved intrinsic properties if found (see Figure 2, green curves). Furthermore, those properties are also preserved after exposure of the heterostructure to air, which confirmed exceptional stability and robustness of graphene-borophene heterostructures. This kind of ambient stability opens new doors to scientific research of borophene as well as to its technological applications.