Borazine (B3N3H6) has recently been shown to form a self-ordered boron nitride overlayer[1], or nanomesh, when dosed onto rhodium(111) single crystal at ~800 °C. This structure consists of 13×13 lattice of h-BN unit cells overlaid on a 12×12 substrate supercell, leading to an overall periodicity of 3.2 nm. This has stimulated substantial interest in the behaviour of this surface, and possible applications, based on the use of the regular array of candidate sites for anchoring metal nanoparticles and molecules.
Nanomesh samples have been prepared on rhodium thin films grown in Si(111) substrates with a yttria stabilised zirconia buffer layer, and imaged using scanning tunnelling microscopy. We have studied the deposition of perylene tetracarboxylic diimide (PTCDI) molecules onto the nanomesh in ultra-high vacuum. Several arrangements of these molecules are observed. Initially, a close-packed phase is formed, however, the nanomesh periodicity can still be imaged through this layer, indicating that the nanomesh is not disrupted. Different scanning conditions show reversal of the substrate contrast, indicating electronic effects are dominating over any topographic variation in the PTCDI overlayer. Upon annealing the substrate, the majority of the molecules either desorb or segregate, leaving a smaller number of molecules trapped in the regular array of adsorption sites of the nanomesh. We discuss the use of this approach to form ordered arrays of well-separated molecules.
The nanomesh is extremely resilient with respect to environmental conditions, and we have imaged it both in ambient conditions, and also under organic solvents such as heptanoic acid. The pores of the nanomesh and overall periodicity of the nanomesh are well resolved when imaging under such liquids.
The possibilities for employing the nanomesh as an inert templating layer in applications are discussed.
[1] Corso M, Auwarter W, Muntwiler M, Tamai A, Greber T, Osterwalder J, Science, 303, pp217-220 (2004) |