Electromagnetic Theory Of Surface-enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is an abnormal optical phenomenon at surface. The Raman signal of molecule absorbed at rough metallic surface is enhanced by six orders of magnitude compared with common Raman signal. It can be enhanced much larger at nanometer-structure surface especially. The surface-enhanced Raman scattering offers high sensitivity and the possibility of detection of monolayer of molecules. For this reason and the additional typical high selectivity of Raman scattering due to the fingerprint nature of the detected spectra, SERS has a large potential for new developments in chemical sensor application. In many respects SERS is a mature topic, having been the subject of numerous reviews. However, SERS is a complex phenomenon. We believe that there exists much work we can do from its mechanisms to its applications.In this thesis, a detailed introduction for the theory of Raman scattering is presented, including the classical mechanism and the quantum one. The optical constants are discussed, which are the refraction index and dielectric constant of metal Au, Ag and Copper. Taking binary rectangular metallic gratings with nanometer dimension as models to simulate the rough surface where Surface-enhanced Raman scattering (SERS) occurs, the electromagnetic mechanism of SERS is investigated. The rigorous couple wave theory is used to quantitatively calculate the diffraction electromagnetic fields for TM-polarized and TE-polarized incident optical wave. We discuss in detail the influence of the grating period, the ratio of grating ridge width to grating period, the depth of grating, the incident optical wavelength and the incident angle on the electromagnetic field. The results show that there exist right matched parameters which enable the diffraction fields to be enhanced. These results proved the enhancement of SERS at rough surface on the electromagnetic mechanism. The grating parameters corresponding to the optimum electromagnetic field enhancement can be a reference for the fabricationof the surface substrates used to be detectors based on the SERS features.