Optical Imaging and Spectroscopy of Airborne Nanowires

Abstract: Semiconductor nanowires are the potential base for building many future devices like solar cells and light emitting diodes. To reach the level of commercialization of such devices, mass production of NWs at low cost with reproducible high quality properties in terms of crystallinity, material and dimensions is a prerequisite. At Lund University a new technique, called Aerotaxy, which satisfies these characteristics, has been developed for continuous production of nanowires in the aerosol phase. Further optimization of Aerotaxy process created the need for in situ, on line and on real time characterization of the aerosol NWs for a quick feedback during growth. For this purpose, I created a new set up for checking the feasibility of photoluminescence spectroscopy, absorption spectroscopy and imaging of the nanowire flow using the polarized and unpolarized scattered light. PL and absorption spectroscopy would be conducted for quality check of nanowires. Furthermore, absorption spectrum from aligned nanowires could possibly give information about their diameter and scattering from aligned nanowires would be tested for correlating the electric field strength used for aligning them to their length. Moreover, imaging of unpolarized scattered laser light would give us information on fluctuations in nanowire flow. Due to insufficient set up components like fiber spectrometer, with poor signal collection efficiency and low quantum efficiency of the chip, in situ PL spectroscopy could not be performed. Scattering of laser light is successfully used for visualizing the nanowire flow which gives an immediate feedback on when the growth is taking place. Scattering experiments of polarized scattered light showed an effect on the direction of the nanowires but because of insufficient number of experiments no conclusions can be drawn. No conclusions also can be drawn for absorption experiments.