Long Vertical Distance Bonding of the Hexagonal Boron Nitride Monolayer on the Cu(111) Surface

The hexagonal boron nitride (hBN) monolayer on the Cu(111) surface has recently been considered an example of an extremely weak hBN/metal interaction, as indicated, e.g., from the presence of an only electronic Moire-like superstructure that was observed in scanning tunneling microscopy images. From these results, a large bonding distance of the hBN sheet to the topmost Cu layer can be envisaged but has not been proven so far. We report a structural analysis of the hBN/Cu(111) interface based on high resolution low energy electron diffraction and normal incidence X-ray standing wave experiments. We find that both the boron and nitrogen atoms are located at very large vertical distances of d(B) = 3.25 +/- 0.02 angstrom and d(N) = 3.22 +/- 0.03 angstrom with respect to the nominal position of the topmost Cu(111) layer. Significant vertical buckling and lateral distortions of the hBN layer can be excluded. These results demonstrate that the hBN monolayer on the Cu(111) surface is indeed well described by a rigid and geometrically well separated sheet.