Electrospinning has been applied to prepare uniaxially aligned nanofibers made of organic polymers, ceramics, and polymer/ceramic composites. The key to the success of this method was the use of a collector consisting of two pieces of electrically conductive substrates separated by a gap whose width could be varied from hundreds of micrometers to several centimeters. As driven by electrostatic interactions, the charged nanofibers were stretched to span across the gap and thus to become uniaxially aligned arrays over large areas. Because the nanofibers were suspended over the gap, they could be conveniently transferred onto the surfaces of other substrates for subsequent treatments and various applications. Materials that have been successfully incorporated into this procedure include conventional organic polymers, graphite carbon, and metal oxides. By controlling the parameters for electrospinning, we have also fabricated a number of simple device structures, for example, an individual nanofiber spanning across two electrodes, 2D arrays of crossbar junctions, and optical polarizers.

The conventional procedure for electrospinning has been modified to generate nanofibers as uniaxially aligned arrays over large areas. The key to the success of this method was the use of a collector composed of two conductive strips separated by an insulating gap of variable width. Directed by electrostatic interactions, the charged nanofibers were stretched to span across the gap and became uniaxially aligned arrays. Two types of gaps have been demonstrated: void gaps and gaps made of a highly insulating material. When a void gap was used, the nanofibers could readily be transferred onto the surfaces of other substrates for various applications. When an insulating substrate was involved, the electrodes could be patterned in various designs on the solid insulator. In both cases, the nanofibers could be conveniently stacked into multi‐layered architectures with controllable hierarchical structures. This new version of electrospinning has already been successfully applied to a range of different materials that include organic polymers, carbon, ceramics, and composites.

This paper describes a solution-based, precursor method for the facile synthesis of uniform nanowires containing rutile SnO2 nanocrystallites. In a typical procedure, nanowires of approximately 50 nm in diameters and up to 30 mum in length were obtained as a white precipitate by refluxing SnC2O4.2H2O and poly(vinylpyrrolidone) in ethylene glycol. Structural analyses by XRD, FT-IR, and TGA indicate that these highly anisotropic nanostructures were formed in an isotropic medium through the aggregation of chainlike precursors that were, in turn, formed via polyol-mediated oligomerization. These nanowires could be further converted to polycrystalline SnO2 by calcination in air at 500 degrees C. The resultant nanowires of SnO2 were highly porous and could be used for gas sensing with improved sensitivity and reversibility under ambient conditions. We have also demonstrated that this new approach could be extended to generate polycrystalline nanowires of other metal oxides such as In2O3 and anatase TiO2.

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Ultrasmooth octadecyltrichlorosilane (OTS) monolayers (2.6 ( 0.2 nm thick, RMS roughness ∼1.0 Å) can be obtained reproducibly by exposing clean native SiO2 surfaces to a dry solution of OTS in Isopar-G. A clean room is not required. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle data, and ellipsometry show that film formation occurs through a "patch expansion" process and terminates once a single monolayer is formed, after about 2 days. These monolayers are suitable as substrates for high-resolution electron beam and AFM or STM lithography. Further observations highlight the importance of controlling water content during deposition of siloxane self-assembled monolayers. OTS covers the surface much faster when there is a little water in the OTS solution; contact angle and ellipsometry data indicate formation of a hydrophobic, 2.6 nm thick film after about 2 h. However, these OTS films have a totally different growth mechanism than films grown from dry solutions and are not really monolayers. The OTS forms platelike islands that then adsorb onto the surface; the resulting overlayers have RMS roughness of more than 3 Å. Continued exposure to the OTS solution results in continued island deposition and increased roughness.