Abstract
Surface atoms have fewer interatomic bonds than those in the bulk
that they often relax and reconstruct on extended two-dimensional
surfaces. Far less is known about the surface structures of nanocrystals.
Here, we show that coherent diffraction patterns recorded from individual
nanocrystals are very sensitive to the atomic structure of nanocrystal
surfaces. Nanocrystals of Au of 3�5 nm in diameter were studied by
examining diffraction intensity oscillations around the Bragg peaks.
Both results obtained from modelling the experimental data and molecular
dynamics simulations strongly suggest inhomogeneous relaxations,
involving large out-of-plane bond length contractions for the edge
atoms (approx0.2 �); a significant contraction (approx0.13 �) for
100 surface atoms; and a much smaller contraction (approx0.05 �)
for atoms in the middle of the 111 facets. These results denote
a coordination/facet dependence that markedly differentiates the
structural dynamics of nanocrystals from bulk crystalline surfaces.
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