Monolayer Borophene Formation on Cu(111) Surface Triggered by ⟨11¯0⟩$\langle {1\bar{1}0} \rangle $ Step Edge

Abstract

Borophene, a promising material with potential applications in electronics, energy storage, and sensors, is successfully grown as a monolayer on Ag(111), Cu(111), and Au(111) surfaces using molecular beam epitaxy. The growth of two‐dimensional borophene on Ag(111) and Au(111) is proposed to occur via surface adsorption and boron segregation, respectively. However, the growth mode of borophene on Cu(111) remains unclear. To elucidate this, scanning tunneling microscopy in conjunction with theoretical calculations is used to study the phase transformation of boron nanostructures under post‐annealing treatments. Results show that by elevating the substrate temperature, boron nanostructures undergo an evolution from amorphous boron to striped‐phase borophene (η = 1/6) adhering to the Cu step edge, and finally to irregularly shaped β‐type borophene (η = 5/36) either on the substrate surface or embedded in the topmost Cu layer. dI/dV spectra recorded near the borophene/Cu lateral interfaces indicate that the striped‐phase borophene is a metastable phase, requiring more buckling and electron transfer to stabilize the crystal structure. These findings offer not only an in‐depth comprehension of the β‐type borophene formation on Cu(111), but also hold potential for enabling borophene synthesis on weakly‐binding semiconducting or insulating substrates with 1D active defects.

Seeking borophene on Ni3Al(111): an experimental characterization of boron segregation and oxidation

“…In the former (monolayer) case, at variance with other growth substrates like e.g. silver [13][14][15][16][17], copper [13,[18][19][20] and gold [21], a purely honeycomb borophene (hB) phase (η HH = 1/3) could be stabilized on the Al(111) termination [16,[22][23][24], where at least 0.5 e − (0.7 e − /atom in this practical case) are transferred from the substrate to each B atom of the borophene monolayer. In principle, one could categorize borophenes at surfaces by classifying them into three subgroups.…”

“…A second case is represented by e.g. the Cu(111) [13,[18][19][20] and Au(111) [21] surfaces, for which formation of borophene monolayers is strictly connected with the bulk dilution, alloying, and surface segregation of B atoms in the respective metals. Finally, the third case is the Al(111) termination [16,[22][23][24].…”