We propose a simple, precise, and wafer-scale fabrication technique for Au double nanopillar (DNP) arrays with nanogaps of several tens of nanometers. An Au DNP was simply constructed by alternately laminating thin layers of Au and polymer on a template and selectively removing the thin layers. This DNP array was expected to exhibit a specific plasmonic property induced by its narrow gap. When measuring the refractive index sensitivity (RIS), Au DNP arrays with 33 nm gaps exhibited a high RIS of 1075 nm RIU(-1) and showed a higher sensor figure of merit than the alternative structures, which did not have a nanogap structure but had almost the same surface area. This indicated that the enhanced plasmon electromagnetic field induced by the nanogap structure improved sensor performance. Our fabrication technique and the optical properties of the nanogap structure will provide useful information for developing new plasmonic applications with nanogap structures.

Super-hydrophobic and super-hydrophilic gold surfaces were prepared by modifying microstructured gold surfaces with thiols. The perfluorodecanethiol (PFDT)-modified rough gold surface was converted from super-hydrophobic (water contact angle 5 150-160u) to super-hydrophilic (0-10u) by photocatalytic remote oxidation using a TiO 2 film. During the remote oxidation, oxygen-containing groups were introduced to the thiol, and finally, even sulfur atoms were removed. Super-hydrophobic/super-hydrophilic patterns were also obtained by photocatalytic lithography, by using a TiO 2 -coated photomask. On the basis of this technique, enzymes and algal cells were patterned on the gold surfaces to fabricate biochips.

A novel technique for solid surface patterning is developed on the basis of the remote oxidation effect of TiO2 photocatalysts. A TiO2-coated quartz plate was faced to a solid substrate, that is, a glass plate modified with an ultrathin organic layer or silicon, copper, or silver plate, separated by a small gap, and the TiO2 was irradiated with UV light in air through a photomask. As a result, two-dimensional images corresponding to the photomask are obtained. Those images are based on the contrasts of nonoxidized to oxidized surfaces.