Control of the area density of vertically grown ZnO nanowires by blending PS-b-P4VP and PS-b-PAA copolymer micelles

We develop a novel and simple method for controlling the area density of ZnO nanowires vertically grown on a Si substrate. The method is based on blending spherical polystyrene-block-poly(acrylic acid) (PS-b-PAA) micelles with polystyrene-block-poly 4-vinylpyridine (PS-b-P4VP) for the area density control of Au nanoparticles, a catalyst of ZnO nanowires, chemically reduced from hydrogen tetrachloroaurate (HAuCl₄) selectively in P4VP core block. No interdiffusion between the two types of block copolymer micelles allows us to fabricate the monolayer of the mixed micelles with the controlled density of Au nanoparticles from which single crystal ZnO nanowires are grown by the VLS method. The number of ZnO nanowires per unit area varies from approximately 15-120 μm^-2 with a tuning capability of more than 800%. Micropatterns with the controlled density of Au nanoparticles are also fabricated by selective pattern transfer of blended micelles.