Reshaping of nanocrystals: Failure of classical nucleation theory

KMC simulations
Top: KMC simulations of the reshaping of a nanoscale Pd
octahedron. Bottom left: master equation (MEQ) formulation
of reshaping. Bottom right: KMC vs MEQ vs CNT predictions.
Scientific Achievement

For reshaping of facetted metal nanocrystals, involving nucleation and growth of new outer layers, we show that classical nucleation theory (CNT) fails to describe behavior. Instead a successful master equation theory is developed.

Significance and Impact

Shape stability is critical for nanocrystals synthesized with facetted non-equilibrium shapes to optimize performance for catalysis, etc. This prompted our development of an appropriate theory for the cooperative many-atom reshaping process to elucidate behavior & aid experiment.

Research Details
  • KMC simulation of a stochastic model for nanocrystal reshaping mediated by surface diffusion quantifies reshaping. 
  • Constrained equilibrium MC simulation for the free energy profile during reshaping reveals the failure of CNT.
  • Our master equation treatment incorporating key nanocrystal configurations succeeds in describing the reshaping barrier.

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