Surface tension induces significant forces on wetted nanostructures, such as vertically oriented nanowire arrays, that can force them to aggregate when dried. This aggregation decreases the homogeneity and surface area of the array, often inhibiting their intended application. These aggregation forces are eliminated by introducing small electric fields ( approximately 100 V/m) during drying, providing a simple approach that is applicable to a broad range of nanowire materials, diameters, lengths, and spacing. A model based on the forces acting on two nanowires shows that electrostatic repulsion, rather than field-induced changes to the surface tension, provides the necessary forces to prevent aggregation. These calculations also highlight the substantial surface tension forces acting on nanostructures and the difficulties associated with preventing their aggregation.

Dye-sensitized solar cells (DSSCs) based on ordered photoanode morphologies, such as nanotubes and nanowires, are widely gaining attention because these geometries are believed to enhance interfacial charge transfer and bulk charge transport. Unfortunately, experimental results have yet to show substantial improvement to conversion efficiency over nanoparticle-based DSSCs. A model is developed to characterize the performance of an idealized photoanode based on an ordered array of transparent conductive nanowires coated with an anatase titania shell. The role of the interfacial electric field in nanowire-based DSSCs is explored computationally by turning electron migration ON or OFF. The results show that back-reaction rates are most strongly influenced by the electric field. These electron loss mechanisms can be reduced by several orders of magnitude, leading to improvements in short-circuit current, open-circuit voltage, and fill factor.

The role of metal interlayers in maintaining adhesion during the direct fabrication of anodic aluminum oxide ͑AAO͒ with high-aspect ratio pores on tin-doped indium oxide ͑ITO͒ is studied. Chromium and titanium interlayers can maintain adhesion while anodization is conducted in either sulfuric, oxalic, or phosphoric acid solutions. However, the ability to form high-aspect ratio pores is dependent on the interlayer and aluminum thickness, the method of aluminum deposition, and possibly the cleaning/ surface treatment of ITO prior to aluminum deposition. AAO films approximately 2 m thick were prepared in oxalic and phosphoric acids, yielding high-aspect ratio pores with length to diameter ratios of 47 and 14, respectively. The distinct stages of pore formation are also correlated with the time-resolved current response of the anodization cell, which provides in situ information about the anodization process so that adhesion can be maintained throughout pore formation. The direct fabrication of AAO on ITO/glass substrates from a single-step evaporation of thick aluminum films enables the formation of smooth and continuous gold nanowires, which have potential applications in photonics.

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Reproducible alignment and complete inclusion of ordered mesoporous structures into anodic aluminum oxide (AAO) is still a challenging nanofabrication process. Hierarchical nanostructures of ordered mesoporous silica (OMS) in AAO channels were prepared directly on conducting substrates by electrophoretic deposition of colloidal silica nanoparticles in sols containing a structure directing agent. The mesoporous silica structures were found to be highly dependent on the magnitude of the applied electric field and moderately dependent on the overall deposition time. At low applied voltages, disordered porous tubules are formed. At an applied voltage of 5 V and deposition times in excess of 7 h, ordered mesoporous silicas fill the AAO channels, and the OMS pores display the onset of axial alignment with respect to the AAO pore. The deposition of the mesoporous silica structures with preferential axial alignment on conductive supports is described by a new self-assembly mechanism based on selective solvent exclusion due to confined particle packing of colloidal silica.