April 1, 2002
Self-assembly is emerging as a powerful, bottom-up method for fabricating materials on the nanometer scale. Such methods are important in the development of next-generation technologies. Self-assembly becomes particularly powerful when the ease and control offered by the assembly of organic materials is combined with the special electronic, magnetic or optical properties provided by inorganic components. The method described here uses a special polymer for the organic material and a variety of metals for the inorganic component. At the Chicago Materials Center, Heinrich Jaeger and graduate student Ward Lopes have developed a versatile approach that involves a hierarchy of multiple levels of self-assembly.
Jaeger and Lopes first spin an ultrathin layer of a diblock copolymer onto a surface. Previous work in our Center has demonstrated how these polymer systems naturally form nanoscale structures. However, the polymers used here cannot be used directly for electronic components because they do not conduct electricity. Jaeger and Lopes have now shown that when this polymer system is exposed to metal vapor, the metal atoms only stick to one of the two pieces of the copolymer.
This technique is capable of generating a range of self-assembled metal-polymer structures, including dense chains of separate nanoparticles and continuous nanowires. Their large anisotropy and very high dielectric contrast makes these materials suitable for nanogratings, interconnects, and sensor applications. These results open up new possibilities for guided, large-scale assembly of hybrid nanostructures.
Figure 1 is a transmission electron micrograph of gold nanoparticle chains (yellow) on a PS-PMMA diblock copolymer template.
Figure 2 shows silver nanowires (blue-grey) on the same type of template. The center-to-center spacing between adjacent chains or wires is 50 nm.
Figure 3 zooms in on one of the patterns to show the individual nanoparticles.
Figures created by Seth B. Darling, Heinrich Jaeger 04/02
References:
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"Hierarchical Self-Assembly of Metal nanostructures on Diblock Copolymer Scaffolds" Ward A. Lopes and Heinrich M. Jaeger, Nature 414 735-738 (2001)