Study of ZnO nanocluster formation within styrene-acrylic acid and styrene-methacrylic acid diblock copolymers on Si and SiO_2 surfaces

摘要

A study of the self-assembly of ZnO nanoclusters on Si and SiO_2 surfaces within the matrices of diblock copolymers, polystyrene-acrylic acid and polystyrene-methacrylic acid, is reported. The polystyrene-acrylic acid and polystyrene-methacrylic acid had block repeat unit ratios of 159-63 and 318-78, respectively. Immiscibility of the two blocks in each copolymer produced microphase separation resulting in the formation of nanosized spherical domains of the minority acid blocks, which served as nanotemplates for the ZnO nanoclusters on both Si and SiO_2 surfaces. The self-assembly process of the nanoclusters was accomplished at room temperature in solution using ZnCl_2 precursor dopant and a dry chemical process using ozone to convert into ZnO. The comparative study showed that the treatment with ozone provided better conversion rate with minimal loss of ZnO than a wet chemical process developed previously. The conversion of ZnCl_2 to ZnO nanoclusters was verified and evaluated by X-ray photoelectron spcctroscopy (XPS). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed spherical morphology for both copolymers with more dense distribution of nanoclusters in the case of the polystyrene-methacrylic acid copolymer. Application of the nanocomposite polymer on large area Si and SiO_2/Si wafer surfaces by static and spin-on casting and photolithographic patterning, metallization, and reactive ion etching processing was developed for surface acoustic wave (SAW) device fabrication.