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The boron nitride nanomesh acts as a scaffold for metal clusters and molecules

The nanomesh pore size of 2 nm makes it as a promising template for a periodic arrangement of molecules or metallic clusters, what is nowadays an important challenge in nanotechnology. And it works out effectively!

The nanomesh is stable under different environments like normal air, water and even acids. In addition, it doesn't decompose up to 1275K under vacuum. This exceptional stability opens a wide range of potential applications of the nanomesh as a scaffold. Here we present two of them.

Gold nanoclusters fit into apertures (diameter about 2 nm) of the nanomesh on Ru.
The first example on the left demonstrates that the nanomesh can act as a template for gold (Au) clusters.
This STM image shows a nanomesh on Ru, on which 0.07 ML of Au has been evaporated at room temperature. The sample was then annealed at 900K for 5 min. This procedure led to the formation of well-defined round Au nanoparticles, which are centered at the nanomesh apertures. No Au particle is found on the wires. Two types of nanoparticles can be seen. The larger ones (see "1" on the figure) are about 4 nm in diameter and up to 1 nm in height. The smaller particles (see "2") fit into apertures and are 1 nm in diameter.
The second example exemplifies the use of the nanomesh pores, which form strong confining potentials, for trapping molecules well above room temperature.

Naphthalocyanine (Nc) molecules were vapor-deposited onto the nanomesh kept at room temperature. These planar molecules have a diameter of about 2 nm, what means that their size is comparable to that of the nanomesh pores (see lower inset). On the STM image on the right it is spectacularly visible how the molecules form a well-ordered array with the periodicity of the nanomesh (3.22 nm). The upper inset shows a region of this substrate with higher resolution. Individual molecules are trapped inside the pores, what indicates a highly site selective adsorption. The interactions between the Nc molecules and the nanomesh dominate the adsorption behavior and interactions between Nc molecules are weak. This behavior is in contrast to Nc on flat graphite for example.

The strength of the trapping potential for Nc is quite strong since only rare hopping events could be observed at room temperature. Annealing to 650K does also not lead to desorption of the molecules from the pores.

STM image of nanomesh on Rh, where Nc molecules only adsorb in pores (diameter of about 2 nm).

Such systems with wide spacing between individual molecules/clusters and negligible intermolecular interactions might be interesting for applications such as molecular electronics and memory elements, in photochemistry or in optical devices. The remarkable stability of a single h-BN monolayer on Rh and Ru paves the way for applications of this material as a template that is not based on expensive ultrahigh vacuum deposition techniques, but on deposition from aqueous solutions, what is much cheaper and therefore commercially very interesting.


 
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| Last update: 25.03.2008 by C. Galli Marxer