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Polarization measurements in tip-enhanced Raman spectroscopy

We investigate the polarization property in tip-enhanced Raman spectroscopy by employing a radial plate consisting of four divided half-wave plates each with a different orientation of the slow axis. The radial plate provides both longitudinal (parallel to the tip axis; p-polarization) and lateral (perpendicular to the tip axis; s-polarization) of the electric field on the sample plane by selecting the proper polarization of the incident field. Single-walled carbon nanotubes, which have strong polarization dependence, are investigated with this polarization control. The radial breathing mode (RBM) and the G-band, which belong to different vibrational symmetries, show opposite polarization dependences. For both p and s-polarization studies, we used a new method for preparing silver probe with a silver particle at the apex. In this method, the probe has been coated with silver colloids by the mirroring reaction. We characterize the morphology of the silver probe by Scanning Electron Microscopy (SEM). A silver particle with diameter ~40 nm which is ideal for localized surface plasmon excitation in the visible wavelength range is formed at the tip apex with high reproducibility. . Experimental Probe preparation; We have used mirroring reaction method for probe preparation. This method is an electroless plating which forms silver surface of well-packed particles on various kinds of substrate such as glass, silicon, silicon nitride, mica, or polymers. The detail of the preparation of silver surfaces on borosilicate glass substrates, which involves the reduction of silver nitrate by glucose, has been previously given in ref [1]. Varying the reaction conditions, principally by varying the concentration of silver nitrate solution, can control the colloidal particle size.