Molecular-level local characterization of nano-materials and development of a STM probe-enhanced Raman spectroscopy system

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In this study, in order to obtain vibrational spectra in nano-regions space selectively, we have developed a measurement system as well as molecular systems for the confirmation of the system performance. The measurement system was assembled by using a scanning probe microscope and a Raman spectroscope. The excitation source for Raman spectroscopy was a 488 nm semiconductor laser and the detector was a cooled charge coupled device. Scanning probes were fabricated by chemical metal plating of silver on mechanically polished Pt/Ir wires. Silver particles were found to be 100-300 nm at the probe points by the use of a scanning electron microscope. Standard samples for space selective detection were prepared with photo-polymerization of a thiophene derivative. Grating structures of polythiophene were fabricated on transparent electro-conductive surfaces with the irradiation of 355 nm interference patterns. Under an optimal condition, structures with 2 micron line width, 3 micron spacing, 200 nm height were produced. The patterned surfaces were measured with the developed measurement system. The average signal intensity of 1400-1550 cm-1 attributed to a stretching vibrational mode of thiophene was measured at 10 x 10 points and spatially mapped. We have confirmed clear grating structures formed on surfaces with this technique. Finally, we obtained some data suggesting that the system has a resolution of about 50 nm.