What is it about?

What does a molecule do when it comes in contact with a very hot surface? We found an answer by studying the high-temperature behaviour of a copper complex on a silica substrate. The question is important because the decomposition of molecules on heated surfaces is a technologically strategic process at the basis of many applications. For instance, in Chemical Vapor Deposition (CVD), the source compounds (the "precursors"), are initially brought into the vapour phase; then, they react on a surface heated at a temperature much higher than that of the carrier vapour phase. At these conditions, activation mechanisms strongly different from those typical of gas-phase or solution chemistry are possible, and novel materials may be synthesized.

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Why is it important?

We detected a new type of surface motion, defined as fast rolling diffusion on the hot surface (T=750 K). This molecular cart-wheeling motion (see movies) was combined with large oscillations of the metal-ligand bond lenghts: the molecule was therefore activated for the decomposition process. Indeed, this type of diffusion might also promote high-energy collisions between rolling molecules on the growth surface. These events could lead to precursor fragmentation and then formation of the first bonds between the metallic centers and the atoms of the growth surface.


What i liked the most about this work, was that it showed very clearly the effects of the drastic conditions of CVD experiments on the structure and behaviour of molecules. We've seen that molecules move fast on the surface, with their bonds elongated: they carry much energy, and are ready to collide, break up and react. I think that this kind of behavior should be general, i.e., when molecules come in contact with surfaces at high temperature conditions, fast rolling diffusion and bond weakening might show up. This has been already found for Zn and Fe complexes on the heated surface of a CVD substrate, even at lower temperatures. In perspective, my personal viewpoint is that this phenomenon might help to explain other important chemical events occurring on surfaces at high temperatures.

Gloria Tabacchi
university of insubria

Read the Original

This page is a summary of: “Hot” Surface Activation of Molecular Complexes: Insight from Modeling Studies, Angewandte Chemie, February 2010, Wiley,
DOI: 10.1002/ange.200907312.
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