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Abstract

Copper nanoparticles on zinc-oxide substrates are discussed as materials for heterogeneous catalysis. An electric field gradient at the contact line between particles, substrate and gas is a possible mechanism for the chemical activity of otherwise only chemically interactive materials. In processing of the nanoparticles an annealing step is employed after deposition on the substrate at moderate temperatures. Experimental studies revealed, that the nanoparticles are sightly sucked into the substrate during annealing that a small crater remains after removing individual particles. In order to reveal the mechanism and the dynamics of this process a phase-field study has been performed. Surface diffusion is assumed to be the underlying physical process for the structural changes of the nanoparticles on the surface. The multi-phase-field theory as implemented in the open-source software OpenPhase has been applied. It is based on the minimization of the free surface energies in the three phase system copper, zinc-oxide and gas. Results of the simulation are presented and compared to the experimental observations. This is a first step in theoretically investigating the multi-physics problem of deformation, piezoelectric activity of the substrate and electrostatic charging of the copper particles. Future work will concentrate the elastic and electric properties of the system in order to reveal the catalytic activity of the compound structure.