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<p>A novel technique of near field imaging has been advanced and used to measure free carrier diffusion length and study optical waveguiding in ZnO nanowires. The technique employs a near field scanning optical microscope (NSOM) and atomic force microscope (AFM) to optically and spatially map cathodoluminescence generated by a scanning electron microscope (SEM). The technique has been advanced from previous work on nanowires by the use of a higher resolution SEM and filtering approximately 90% of any background luminescent signal directly generated in the AFM/NSOM probe. For diameters between 250 nm and 800 nm, the diffusion length was found to vary with diameter. For diameters greater than 800 nm, the diffusion length is relatively constant. This is only the second such diameter dependence measurement for ZnO nanowires, and the only measurement for this nanowire diameter range. The full width at half maximum (FWHM) of the waveguiding output distribution from a single nanowire was found to be uncorrelated with the carrier excitation rate for a 60x increase in excitation rate. Luminescence of 380 nm was shown to propagate in the nanowire to a distance of 20-30 mm, indicating an absorption coefficient of ~2000 cm-1.
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<br>Subjects: ZnO; Near-field scanning optical microscopy; NSOM; Diameter dependence; Waveguiding; Transport imaging; Diffusion length</div>
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Little, Anree G.</div>
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