Block copolymer micellar thin films as templates for the production of tunable inorganic nanocluster arrays and their applications

Abstract

In the past decade, the use of self-assembling systems for the fabrication of materials on the nanometer scale has been an active area of research. Block copolymer thin films are a subclass of' self-assembling systems that have received considerable attention due to their intrinsic nanometer feature size, their ease of synthesis, and their rich phase behavior. While block copolymer thin films have been utilized in a variety of applications, including the nanofabrication of substrates, the modification of surface properties, and the synthesis of photonic structures, this thesis will focus on using the self-assembling properties of block copolymer thin films to synthesize inorganic nanocluster arrays. These arrays have a wide range of possible applications in fields such as catalysis, data storage, and nanofabrication. This thesis demonstrates a general route for using block copolymer micellar thin films as templates to synthesize tunable inorganic nanocluster arrays. The approach utilized amphiphilic block copolymers, such as poly(styrene-block-acrylic acid) and poly(styrene-block-2-vinylpyridine), to create micelles in solution that could be selectively loaded with metal ions and deposited onto a substrate to create quasi-hexagonal arrays of nanoclusters.

(cont.) Various strategies were successfully developed to tune the size and areal density of the nanoclusters, thereby affording a level of control that is unique relative to the standard routes for synthesizing inorganic nanocluster arrays. The strategies included the variation of the block copolymer molecular weight, the addition of polystyrene homopolymer into the micellar solution, and the mixing of different micellar solutions. The block copolymer micellar system was utilized to create iron oxide nanoclusters, which were catalytically active in the thermal chemical vapor deposition growth of carbon nanotubes (CNTs). Through appropriate selection of the substrate and the reaction conditions, vertical CNT growth was achieved. By uniformly varying the areal density of iron oxide nanoclusters on the substrate surface, the morphology of the CNT films was manipulated from a tangled and sparse arrangement of individual CNTs, through a transition region with locally bunched and self-aligned CNTs, to rapid growth of thick vertical CNT films. Through a microcontact printing approach, nanocluster arrays were patterned on a micron scale to synthesize patterned vertical growth of CNTs. To demonstrate the generality of this approach, the block copolymer micellar system was also used to synthesize gold nanocluster arrays for fabricating DNA arrays via Supramolecular Nano-Stamping (SuNS).