Hierarchically built hetero-superstructure arrays with structurally controlled material compositions.

Abstract

Hierarchical assemblies are repeatedly encountered in nature, and when replicated in synthetic patterns and materials, can enhance their functionality or impart multifunctionality. In order to assemble a hierarchical superstructure that consists of components made up of multiple nanostructures, control over placement and stoichiometry is desirable. Macroscopic arrays that present up to three levels of hierarchy are demonstrated here and are achieved using the self-assembly of soft, collapsible block copolymer nanospheres for the first two levels, followed by directed self-assembly of metal nanospheres for the third. The fabrication approach combines advantages of soft sphere self-assembly to yield non-close-packed and variable array pitch values, with the inherent chemical functionality presented by the polymer-based soft spheres; these assemblies can then be transformed into a range of different materials, including metal or semiconductor nanostructures, or further tailored with an additional level of complexity. Structural investigation shows the superstructure formation to be governed by generic design rules that can be extended across different material combinations.