Study of Ultrasensitive Nanoscale Spectroscopy using Electric Field Enhancement

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(1)In-situ transmission electron microscopy (TEM) experiments revealed that dimples formed in hexagonal thin crystals by irradiation of a focused TEM electron beam recovers to flatten the surface under a subsequent electron irradiation with a moderately defocused beam. The electron-stimulated recovery can be attributed neither to knock-on damage nor beam heating effects but to electronically enhanced self-diffusion in the GaN crystals.(2A)when the sample tip gap of STM was irradiated by chopped light, the light generates modulated tunneling current which is proportional to the second order differential of Voltage-Current curve and the square of light electric field. A modulated bias voltage of frequency fv applied to tip sample gap generates modulated tunneling current of frequency 2fv which is proportional to the second order differential of Vaoltage-Current curve. By comparing these two modulated signals, we can estimate quantitatively the light electric field beneath the STM tip including enhancement effects. We have successfully measured the magnitude of light enhancement on HOPG surface in situ.(3B)Drastic light enhancements over two orders were observed even with W tips and Pt tips, although expected magnitudes of enhancement for these materials estimated from surface plasmon mechanism were less than fifty. It was revealed that ordinally STM tips have a large amount of enhancement effects.