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Hierarchical self-assembly of metal nanostructures on diblock copolymer scaffolds

Abstract

Self-assembly is emerging as an elegant, ‘bottom-up’ method for fabricating nanostructured materials1,2,3,4,5,6,7,8. This approach becomes particularly powerful when the ease and control offered by the self-assembly of organic components is combined with the electronic, magnetic or photonic properties of inorganic components2,5,9. Here we demonstrate a versatile hierarchical approach for the assembly of organic–inorganic, copolymer–metal nanostructures in which one level of self-assembly guides the next. In a first step, ultrathin diblock copolymer films form a regular scaffold of highly anisotropic, stripe-like domains10,11,12. During a second assembly step, differential wetting guides diffusing metal atoms to aggregate selectively along the scaffold, producing highly organized metal nanostructures. We find that, in contrast to the usual requirement of near-equilibrium conditions for ordering2,3,13, the metal arranged on the copolymer scaffold produces the most highly ordered configurations when the system is far from equilibrium. We delineate two distinct assembly modes of the metal component—chains of separate nanoparticles and continuous wires—each characterized by different ordering kinetics and strikingly different current–voltage characteristics. These results therefore demonstrate the possibility of guided, large-scale assembly of laterally nanostructured systems.

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Figure 1: Transmission electron microscopy (TEM) image of ultrathin diblock copolymer film.
Figure 2: Metal nanochain and nanowire formation on PS-b-PMMA at different stages during the second self-assembly level.
Figure 3: Comparison of Monte Carlo simulation (left column) and experimental results (right column) for Ag nanowire formation.
Figure 4: Electronic transport measurements on self-assembled nanochains (a) and nanowires (b).

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Acknowledgements

We thank T. Witten, S. Coppersmith, T. Morkved, M. Möller and K. Shull for discussions, and R. Parthasarathy for help with some of the IV measurements. This work was supported by the MRSEC programme of the NSF and by the W. M. Keck Foundation.

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Correspondence to Heinrich M. Jaeger.

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Lopes, W., Jaeger, H. Hierarchical self-assembly of metal nanostructures on diblock copolymer scaffolds. Nature 414, 735–738 (2001). https://doi.org/10.1038/414735a

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