Abstract
Major progress in the crystal growth of nanowires and related structures places new demands on our abilities to characterize optical and electronic properties with both an ease and a resolution commensurate with the materials of interest. In particular, transport properties, such as minority carrier diffusion length, are important for a range of applications in light emission, sensing and solar energy conversion. In this paper, a technique to “image transport” in nanostructures by monitoring the motion of charge via the recombination emission of light is reviewed. Transport imaging combines the resolution of near-field optics with the charge generation control of a scanning electron microscope. The technique is related to, but significantly different from standard cathodoluminescence, since it maintains the spatial information of the emitted light. Light is collected in the near-field from a scanning fiber in an atomic force microscope/near-field scanning optical microscope system. It is possible to determine minority carrier or exciton diffusion lengths from a single optical image, without any electrical contact to the sample. New results are presented for minority carrier hole transport in ZnO nanowires and nanobelts.
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