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

Synthesis of a stable, well ordered honeycomb borophene (hB) phase has been achieved to date by exploiting Al(111) as a growth substrate, which provides the necessary charge doping to compensate the high hexagonal-holes density. However, B/Al(111) is governed by a strong B–Al interaction so to yield the actual formation of an AlB2 hB phase. Dilution of aluminum by alloying could then in principle weaken the boron-support bonding. By means of a combined spectroscopy and microscopy experimental approach, we find instead that the growth of boron layers on the Ni3Al(111) alloy termination is driven by B dissolution into the bulk and surface segregation mechanisms. While no long-range ordered boron-induced phase is observed, locally ordered superstructural units with triangular appearance are stabilized by substrate pinning, following the chemical p(2 × 2) surface order. Oxidation involves both boron and aluminum, inducing surface segregation of B, while nickel remains in its metallic form.