We demonstrate a large-scale production of aligned SnO 2 nanofibers with a multi-nozzle electrospinning method combined with an air-shield enclosed rotating drum collector. The production rate by this multi-nozzle approach is several times higher than that of the single-nozzle electrospinning. The nanofibers produced were having a short range of diameters similar to the case of nanofibers produced by single nozzle electrospinning. The well-aligned nanofibers are subsequently processed into vertically oriented SnO 2 nanowires on an FTO substrate. The average diameter and length of the wires were 75 AE 25 nm and 19 AE 2 mm, respectively. Dye-sensitized solar cells using this nanostructured material as the working electrode yielded a short-circuit current density (J sc ) of 9.9 mA cm À2 (which is 42% higher than that achieved by nanowires produced by other methods), an open-circuit voltage (V oc ) of 0.525 V and a power conversion efficiency (h) of 2.53%. We believe that improvement of the multinozzle electrospinning is highly promising for commercialization due to simplicity and easiness of fabricating the spinneret, control over the diameter and spatial orientation of the fibers.
A method for analysing the formation of electrical contacts to single silicon nanowires (Si NWs) by exploiting scanning electron microscopy (SEM) images, using active secondary electrons voltage contrast, is presented. Our approach clearly demonstrates the advantages of the proposed technique in analysing multiple contacts to a single nanowire simultaneously, in comparison to the conventional voltage contrast technique, where only two contact structures can be analysed, mainly for studies of the material dopant’s profile. The SEM is equipped with an in-lens detector, which collects the secondary electrons generated during electron beam exposure of the sample. Biasing the contacts with different voltages has been used to analyse the metal to Si NW contacts. The secondary electrons are sensitive to the potential distribution and the contrast of the SEM image changes depending on the number of secondary electrons detected. The Si NWs also vary their contrast together with the electrodes if they are properly electrically contacted. The basic tools and fixtures required for such measurements, and the corresponding image processing algorithms are described.
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