First principles studies of Carbon ring formation underneath of hexagonal boron nitride growth on Rh(111)*

Hexagonal boron nitride (h-BN), grown on Rh(111) forms a Moiré pattern with elevated (rim) and depression (valley) areas.The presence of the native carbon impurities in Rh potentially gives rise to the formation of hexagonal carbon rings under every other rim area as suggested by recent experiments [1] and could lead to new structures and novel chemistry.Here, on the basis of Density Functional Theory (DFT) simulations with dispersion corrections, we show that these rings tend to grow in a manner in which the center of each ring is placed on top of the Rh atom. These rings grow next to each other and form islands which are separated from each other by an equal distance while the BN monolayer remains untouched. Our simulations of Scanning Tunneling Microscope (STM) images from this structure, in good agreement with experimental data for number of rings from 3 to 5.The calculations of local variations in work function also show that these variations become more pronounced by growth of islands.This results show that by control of the concentration of local impurities underneath the rim areas in BN, the chemical properties are modified and the monolayer could be engineered for interesting chemical reactions. [1] Koslowski et al. Private communication.