Single-Layer Model of the Hexagonal Boron Nitride Nanomesh on the Rh(111) Surface

An alternative model of the hexagonal boron nitride ($h$-BN) on nanomesh on the Rh(111) surface is presented. It explains the observed ultraviolet photoelectron spectroscopy spectra and reproduces experimental STM images introducing, instead of two, only one strongly corrugated layer of $h$-BN covering the whole Rh surface. In order to optimize the geometry of the BN layer we calculate the forces by density functional theory and analyze the interactions in the system. The final geometry is a result of a competition between BN-metal attraction or repulsion and elastic properties of the isolated $h$-BN layer. The calculated bonding energy is around 0.33 eV per BN molecule with a corrugation close to 0.55 Å.

Figure 1

The $z$ dependence of the force acting on B and N atoms of a flat $h$-BN monolayer in (fcc, top) configuration and relaxation of the first metal layer. Note that at equilibrium the $h$-BN layer is buckled with B and N at 2.04 Å and 2.18 Å away from the metal surface, respectively.

Figure 2

Surface map of the $z$ force component acting on N and B atoms. The calculations are performed with a flat BN layer placed 2.17 Å [(a), (b)] and 2.57 Å [(c), (d)] from the surface. When N is positioned at ($x$, $y$, $z$), B is at ($x+2/3$, $y+1/3$, $z$).

Figure 3

The atomic structure of the $h\mathrm{\text{−}}\mathrm{BN}/\mathrm{Rh}(111)$ nanomesh. (a) Contour map of the $z$ coordinate of N atoms in the $3\times 3$ nanomesh unit cell. (b) Ball and stick model of the $h\mathrm{\text{−}}\mathrm{BN}/\mathrm{Rh}(111)$ nanomesh unit cell (with just one metal layer). Colors indicate the height of the B and N atoms.

Figure 4

$\mathrm{N}\mathrm{\text{−}}{p}_{,y}$ density of states calculated for low (N-top, B-fcc) and high (N-fcc, B-hcp configurations) regions.