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Coordination-dependent surface atomic contraction in nanocrystals revealed by coherent diffraction


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 (0.2 Å); a significant contraction (0.13 Å) for {100} surface atoms; and a much smaller contraction (0.05 Å) 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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Figure 1: Coherent electron diffraction pattern recorded from a single, faceted, Au nanocrystal (4 nm in size).
Figure 2: Experimental diffraction intensities of a Au nanocrystal and their modelling.
Figure 3: Bond length distributions in the Au nanocrystal obtained by modelling the experimental diffraction pattern.
Figure 4: Surface atom contraction obtained from the molecular dynamics simulation.


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The work was supported by NSF Career Award, DMR 0449790 (W.J.H., J.M.Z.), DOE DEFG02-01ER45923 (R.S., J.T., J.M.Z.) and DEFG02-03ER15476 (R.G.N., L.D.M.). The electron microscopy work was carried out in the Center for Microanalysis of Materials, University of Illinois, which is partially supported by the US Department of Energy under grant DEFG02-91-ER45439.

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W.J.H., R.S., J.T. and J.M.Z. carried out the diffraction experiment, modelling and analysis. L.D.M. and R.G.N. carried out particle synthesis.

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Correspondence to J. M. Zuo.

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Huang, W., Sun, R., Tao, J. et al. Coordination-dependent surface atomic contraction in nanocrystals revealed by coherent diffraction. Nature Mater 7, 308–313 (2008).

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