Utilizing near-field and depolarization effects for tip-enhanced Raman spectroscopy on semiconductor nanostructures

Noble metal particles show very interesting and complex optical properties. One of the most striking phenomena encountered in these particles are electromagnetic resonances due to collective oscillations of the conduction band electrons. The excitation of plasmons leads to an increased light scattering and to an enhanced electromagnetic near-field in the vicinity of these particles. The depolarization of the incident light excites additional modes usually not observed in the far-field spectra. Therefore, beside the far-field polarization modes, the observed Raman enhancement contains also near-field contributions and additional modes excited by the scattered light. These contributions can be exploited to improve the optical resolution of conventional Raman spectroscopy thus allowing the characterization of stress in semiconductor structures on the nano-meter scale. For the evaluation of the achieved resolution, TERS scans across silicon-germanium line structures were performed