TiO2 nanoparticle arrays prepared using a nanosphere lithography technique

A nanosphere lithography technique has been used to synthesize periodic nanoparticle arrays of TiO2 on glass substrates. Both monolayer and bilayer evaporation masks were generated from hexagonally close-packed polystyrene nanospheres, each one producing a different array of TiO2 nanoparticles. Atomic force microscopy (AFM) showed that the masks typically consisted of ordered 10-100 mum(2) domains. X-ray photoelectron spectroscopy confirmed that the surface composition of the particles corresponded to TiO2 with minor amounts of a Ti3+ species, presumably associated with edges, corners, and oxygen vacancy defects. Analysis of the AFM images indicated that the nanoparticles were circular in shape with array dimensions approximately consistent with simple geometric considerations for the 420 nm diameter polystyrene nanospheres used as masks in this work. The monolayer and bilayer masks yielded TiO2 particle diameters of 169 +/- 12 nm and 140 +/- 13 nm, respectively. The absorption edge of the nanoparticle arrays are blue-shifted from single-crystal rutile.