SURFACE SCIENCE

Buckled BN

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Science  30 Mar 2007:
Vol. 315, Issue 5820, pp. 1769
DOI: 10.1126/science.315.5820.1769a

A covalently bonded overlayer on a metallic surface can be distorted to varying degrees, depending on the extent of lattice mismatch. For example, boron nitride (BN) overlayers can form simple monolayers on close-packed Cu(111) and Ni(111) surfaces, but complex moiré patterns are observed on Pt and Pd surfaces. On Rh(111) and Ru(111) surfaces, scanning tunneling microscopy helped reveal the formation of “nanomeshes” in which 2-nm depressions formed a hexagonal lattice with a 3-nm periodicity. For the Rh system, this pattern was initially attributed to a bilayer structure in which the depressions were holes exposing the underlying metal. Laskowski et al. now propose an alternative structure that better explains the ultraviolet photoelectron spectra for this surface and that avoids the energetic penalty posed by the many dangling bonds in the two-layer structure. Density functional calculations were used to create a force field for a BN layer strained by 8%, its lattice mismatch with Rh(111). When this overlayer was allowed to relax on the Rh(111) surface, it adopted a nanomesh geometry of flat depressions (“holes”) where the lattice match with the substrate was high, surrounded by a region about 0.6 Å higher, where poor lattice matching led to overlayer repulsion. This steplike corrugation in the surface normal direction relieves strain while maintaining the lateral dimensions of the BN layer. — PDS

Phys. Rev. Lett. 98, 106802 (2007).

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