Synthesis of semiconducting ceramic nanofibers, development of p-n junctions, and bandgap engineering by electrospinning.

摘要

Nanostructured semiconducting metal oxides, such as nanotube, nanowires, nanoribbons and nanofibers are of considerable interest for solar energy conversion, sensors and in various electronic applications. Nanoscale structures especially, nanofibers have unusually high aspect ratio and hence, very high surface area per volume ratio. The characteristic high surface area per unit mass of nanofibers provides detecting sensitivity of part per million and even below, and decrease the response time remarkably in comparison with thin film materials. In this work, several semiconducting metal oxide nanofibers are synthesized by sol-gel processing followed by electrospinning. Fibers are made of ZnO, TiO2 , Al2O3, NiO, CuO, SnO2, TiO2 /Al2O3, TiO2/ZnO, Al doped ZnO, and In doped ZnO materials. The diameters of these electrospun ceramic nanofibers range 50--300 nm. Different analytical techniques are used to characterize ceramic nanofibers which include scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Fourier transform infra red spectroscopy (FTIR), UV-Vis spectroscopy, electrical property (I-V, conductivity) measurements. Fibers are made as randomly oriented fiber mat as well as axially oriented nanofibers in yarns. Making the nanofibers into a twisted nanofiber yarn provides the macroscopic handling capability of the nanofibers while retaining some of the nanoscale properties of materials. Ceramic nanofiber p-n junctions are developed using twisted nanofiber yarns of ZnO and NiO which clearly showed rectifying I-V properties at dark (non-illuminated) condition.;Bandgap energy of ZnO nanofibers are engineered by co-electrospinning of ZnO precursor with dopants (Al or In) in the precursor solution. Doping of ZnO nanofiber matrix with Al and In materials brings about significant structural, electrical, and optical property modification. The optical bandgap energy increases with the addition of Al dopants in the ZnO nanofiber matrix while the bandgap energy of In doped ZnO nanofibers decreases with the increasing concentration of In dopants in the ZnO matrix. Electrospinning proved to be a simple, low cost, and reliable technique for dopant incorporation to attain modified structural, electrical, and optical properties of these semiconducting nanofibers.