  Hexagonal boron nitride (h-BN) nanomesh, a two-dimensional insulating
monolayer, grown on the (111) surface of rhodium exhibits an intriguing
hexagonal corrugation pattern with a lattice constant of 3.2 nm. Despite
numerous experimental and theoretical studies no quantitative agreement has
been found on some details of the adsorption geometry such as the corrugation
amplitude. The issue highlights the differences in chemical and electronic
environment in the strongly bound pore regions and the weakly bound wire
regions of the corrugated structure. For reliable results it is important to
probe the structure with a method that is intrinsically sensitive to the
position of the atomic cores rather than the electron density of states. In
this work, we determine the corrugation of h-BN nanomesh from angle- and
energy-resolved photoelectron diffraction measurements with chemical state
resolution. By combining the results from angle and energy scans and comparing
them to multiple-scattering simulations true adsorbate-substrate distance can
be measured with high precision, avoiding pitfalls of apparent topography
observed in scanning probe techniques. Our experimental results give accurate
values for the peak to peak corrugation amplitude (0.80 A), the bonding
distance to the substrate (2.20 A) and the buckling of the boron and nitrogen
atoms in the strongly bound pore regions (0.07 A). The results are important
for the development of theoretical methods involving the quantitative
description of van der Waals systems like it requires the understanding of the
physics of two-dimensional sp2 layers.
