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Coerced mechanical coarsening of nanoparticle assemblies


Coarsening is a ubiquitous phenomenon1,2,3 that underpins countless processes in nature, including epitaxial growth1,3,4, the phase separation of alloys, polymers and binary fluids2, the growth of bubbles in foams5, and pattern formation in biomembranes6. Here we show, in the first real-time experimental study of the evolution of an adsorbed colloidal nanoparticle array, that tapping-mode atomic force microscopy (TM-AFM) can drive the coarsening of Au nanoparticle assemblies on silicon surfaces. Although the growth exponent has a strong dependence on the initial sample morphology, our observations are largely consistent with modified Ostwald ripening processes7,8,9. To date, ripening processes have been exclusively considered to be thermally activated, but we show that nanoparticle assemblies can be mechanically coerced towards equilibrium, representing a new approach to directed coarsening. This strategy enables precise control over the evolution of micro- and nanostructures.

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Figure 1: Coerced coarsening of a nanoparticle assembly.
Figure 2: Evolution of an ensemble of nanoparticle islands.
Figure 3: Change in the position of the peak in the radially averaged Fourier transform of images of evolving ensembles of nanoparticle islands.
Figure 4: Scaled island size distributions for a nanoparticle island ensemble subject to mechanically driven coarsening.


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We are grateful for the financial support of the UK Engineering and Physical Sciences Research Council and the EU Framework Programme 6 Marie Curie Research Training Networks scheme (under grant MRTN-CT-2004005728 (PATTERNS)). The grazing incidence small angle X-ray scattering work was performed on the EPSRC-funded XMaS beam line at the ESRF, directed by M.J. Cooper and C. Lucas. We are grateful to the beam line team of S.D. Brown, L. Bouchenoire, D. Mannix, D.F. Paul and P. Thompson for their invaluable assistance, and to M. Everard, C. Nicklin and R. Williams for both collaborating on the SAXS experiments and for helpful advice related to nanoparticle synthesis. We also would like to very gratefully acknowledge extremely helpful discussions with P. Mulheran, J.P. Garrahan, and members of the PATTERNS RTN (in particular, U. Thiele and U. Steiner).

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Authors and Affiliations



M.O.B. and P.J.M. conceived and designed the experiments. M.O.B., M.A.-T., E.P.-V., and P.S. performed the experiments. M.O.B., C.P.M., and P.J.M. analysed the data. C.P.M., P.N., and M.B. contributed materials/analysis tools. M.O.B. and P.J.M. co-wrote the paper.

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Correspondence to M. Brust or P. J. Moriarty.

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The authors declare no competing financial interests.

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Blunt, M., Martin, C., Ahola-Tuomi, M. et al. Coerced mechanical coarsening of nanoparticle assemblies. Nature Nanotech 2, 167–170 (2007).

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