Two-dimensional silicon boride on ZrB2(0001)

Abstract

A two-dimensional silicon boride phase, ``siliborophene,'' was formed on a ${\mathrm{ZrB}}_{2}$(0001) single-crystal surface, which coincided with the $2\ifmmode\times\else\texttimes\fi{}2$ periodicity of the substrate. The phonon dispersion relations were measured using high-resolution electron energy-loss spectroscopy and were compared with theoretical predictions based on first-principles density functional theory. Among many theoretically derived surface models, only one structure made of ${\mathrm{Si}}_{3}{\mathrm{B}}_{6}$ can reproduce details of the measured phonon dispersion. That model consists of a cyclic boron ring ($c{\mathrm{B}}_{6}$) capped by a Si atom, ${\mathrm{SiB}}_{6}$ group, and $s{p}^{2}$-like Si atoms connecting them. This structure is much more robust than that of silicene: it shows no order--disorder transition until 1300 K; above that temperature, Si is desorbed gradually. Electron band calculation of the isolated film of ${\mathrm{Si}}_{3}{\mathrm{B}}_{6}$ displays a band crossing at the $\overline{\mathrm{K}}$ point, which makes this material promising for use with Fermi-level engineering.