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We present a novel technique to tune the plasmon resonance of metal-coated silicon tips in the whole visible region without altering the tips original sharpness. The technique involves modification of the refractive index of silicon probe by thermal oxidization. Lowering the refractive index of silicon tip coated with metal shift the plasmon resonance of the metallic layer to shorter wavelength. Numerical simulation using FDTD agrees well with the empirical results. This novel technique is very useful in tip-enhanced Raman spectroscopy studies of various materials because plasmon resonance can tuned to a specific Raman excitation wavelength. Controlling the plasmon resonance wavelength in metal-coated probe using refractive index modification Atsushi Taguchi, Norihiko Hayazawa, Yuika Saito, Hidekazu Ishitobi, Alvarado Tarun, and Satoshi Kawata Optics Express, Vol. 17, Issue 8, pp. 6509-6518 (2009)     (a) FDTD Model representing the Ag-coated oxidized Si probe that consists of Si, SiO2, and Ag layers. (b) Calculated near-field spectra of the Ag-coated oxidized Si probes with different SiO2 thicknesses. (top) TEM images of the Si probes for after 30 s oxidization, (bottom)SEM images of Ag-coated oxidized probe Scattering spectra of (a) Ag-coated oxidized Si probe and (b) Ag-coated non-oxidized Si probe. Inset shows a spectrum of the halogen lamp used for the illumination.