Friday, November 12, 2010: 10:10 AM
Seminar Theater (Hilton)
Interest in nanowire arrays has grown dramatically in the last decade due to beneficial properties that are specific to this particular morphology in optoelectronics, catalysis, surface modification, as well as energy storage and conversion. Particularly important in optical applications is the fabrication of these arrays on transparent conductive supports. The direct fabrication of nanoporous templates, such as anodic aluminum oxide, on a transparent conductive oxide support is a potentially low cost step towards the growth of high-density arrays of nanowires with tunable aspect ratios. However, template removal or additional processing of the nanowire arrays can lead to nanowire aggregation if liquids are used. This aggregation decreases the uniformity and surface area of the substrate, resulting in decreased light transmission or device performance. Current methods for fabrication of anodic aluminum oxide templates on transparent conductive oxides are highly sensitive to delamination, while existing techniques to prevent nanowire aggregation utilize high energy and pressure processing. Here we present simple approaches to control these interfacial forces in the fabrication of nanowire arrays. Thin adhesive interlayers are first used to aid in the direct fabrication of anodic aluminum oxide on indium tin oxide substrates. A variety of aspect ratios can be obtained depending on such factors as aluminum film thickness, interlayer composition and thickness, and anodization electrolyte. Furthermore, a simple and scalable method to reduce or eliminate capillary coalescence of the nanowire array is developed. This method induces a capacitance layer on the surface of the wetted nanowire array, which not only reduces the surface tension of the drying fluid but also causes the nanowires to reach a Coulombic equilibrium with one another that prevents aggregation. Furthermore, as an example of device fabrication utilizing these methods, core/shell nanowire arrays are fabricated as photoanodes in dye-sensitized solar cells.