Depositing boron on Cu(111): Borophene or boride?

TL;DR

This study clarifies that boron deposition on Cu(111) forms copper boride, not borophene, through systematic experiments and calculations, resolving previous controversies about the surface structures.

Contribution

The paper provides definitive experimental and theoretical evidence that boron on Cu(111) forms copper boride, not borophene, advancing understanding of surface reactions and material synthesis.

Findings

Confirmed formation of copper boride via STM, XPS, and ARPES.

Boron reacts with Cu at edges or defects, leading to copper boride structures.

First-principles calculations support experimental results and reveal formation mechanisms.

Abstract

Large-area single-crystal surface structures were successfully prepared on Cu(111) substrate with boron deposition, which is critical for prospective applications. However, the proposed borophene structures do not match the scanning tunneling microscopy (STM) results very well, while the proposed copper boride is at odds with the traditional knowledge that ordered copper-rich borides normally do not exist due to small difference in electronegativity and large difference in atomic size. To clarify the controversy and elucidate the formation mechanism of the unexpected copper boride, we conducted systematic STM, X-ray photoelectron spectroscopy and angle-resolved photoemission spectroscopy investigations, confirming the synthesis of two-dimensional copper boride rather than borophene on Cu(111) after boron deposition under ultrahigh vacuum. First-principles calculations with defective surface models further indicate that boron atoms tend to react with Cu atoms near terrace edges or defects, which in turn shapes the intermediate structures of copper boride and leads to the formation of stable Cu-B monolayer via large-scale surface reconstruction eventually.