Synthesis of Atomically Thin Boron Films on Copper Foils

Abstract

Two-dimensional boron materials have recently attracted extensive theoretical interest because of their exceptional structural complexity and remarkable physical and chemical properties. However, such 2D boron monolayers have still not been synthesized. In this report, the synthesis of atomically thin 2D γ-boron films on copper foils is achieved by chemical vapor deposition using a mixture of pure boron and boron oxide powders as the boron source and hydrogen gas as the carrier gas. Strikingly, the optical band gap of the boron film was measured to be around 2.25 eV, which is close to the value (2.07 eV) determined by first-principles calculations, suggesting that the γ-B28 monolayer is a fascinating direct band gap semiconductor. Furthermore, a strong photoluminescence emission band was observed at approximately 626 nm, which is again due to the direct band gap. This study could pave the way for applications of two-dimensional boron materials in electronic and photonic devices.

Rediscovering the Crystal Chemistry of Borides

“…[377] However, note that borophene is not the only single-layer allotrope of boron, as single-layer γ-boron has also been grown on copper foils through chemical vapor deposition with oxygen. [378] MAX phases (usually M n+1 AlC n ) have been exfoliated through the chemical etching of the aluminum layer, leaving behind a metal carbide layer more commonly known as MXene. These MXenes have been used in electrochemical devices owing to both their high surface area and their high electrical conductivities.…”

Two-dimensional magnetic boron

“…Fortunately, a breakthrough was just made that boron sheets can be grown on the Ag (111) surface under pristine ultra-high vacuum conditions or on copper foils by using chemical vapor deposition (CVD). [26][27][28][29] To resolve the crystal structures of several samples, 26 we focused on some lowenergy 2D structures with hexagonal or rectangular symmetry, which should match the lattice of Ag (111) substrate very well. This resulted in a serendipitous discovery of M -boron.…”

Prediction of Two-Dimensional Phase of Boron with Anisotropic Electric Conductivity

“…Due to the symmetry of the W substrate, however, these structures are quite different from the ones reported previously. 5,16,17 Their most distinct feature is that they are composed of both four-membered and six-membered boron rings, where the formation of the four-membered rings can be regarded as a compromise in order to match the substrate structure as much as possible. First, boron atoms tend to form an epitaxial skeleton, matching the distribution of tungsten atoms.…”