Comparative study of self-assembled ZnO nanostructures in poly(styrene-acrylic acid) diblock copolymers-[PS]m/[PAA]n-on Si and SiO2/Si surfaces

A comparative study of the structural characteristics exhibited by the self-assembled ZnO nanoclusters developed on Si and SiO2/Si surfaces using diblock copolymers of styrene-acrylic acid, [PS]m/[PAA]n, with block repeat unit ratios m/n of 159/63 and 106/17, is reported. These copolymer systems are expected to have self-assembled nanosized spherical domains of the minority acid blocks in solid phase but with domain sizes dependent on their respective block ratios and molecular block lengths. Templating of the ZnO nanoclusters with these copolymer systems enabled the development of the nanoclusters with two different size distributions on the Si and SiO2/Si surfaces. The templating process involved the incorporation of a ZnCl2 precursor into the functional group of the acid blocks in liquid phase at room temperature, application of the doped solution onto the surfaces by spin-casting for the formation of the thin nanocomposite film with ZnCl2 nanoclusters and subsequent conversion into ZnO by a dry ozone process. The ZnO nanoclusters in the [PS]159/[PAA]63 copolymer and [PS]106/[PAA]17 copolymer were found to have a size distribution of 250-350 and 40-140 nm, respectively. Over-doping with ZnCl2 precursor resulted in increased size of nanoclusters due to agglomeration in both copolymer systems