Development of periodically structured SERS substrates and its application to ultra-sensitive molecular detection

Surface Enhanced Raman Scattering (SERS) is one of the methods to improve the weakness of Raman Spectrum. The mechanisms that makes SERS improve the signal intensity are: the electric field enhancement and the carrier transmission enhancement. According to the fact that electric field effect can provide a stronger enhancement than the chemical effect, numerous scientists commence to do a lot of research on the electric field effect of SERS. If the electric field effect is going to be implemented to enhance the Raman Intensity, solving the problem of the SERS-active substrate is a necessity. As the nano technique matures, various types of SERS-active substrates are fabricated. Nevertheless, most of substrates, which is designed for the enhancement of surface plasmon effect, are sphere liked, tip liked and metal evaporated. Therefore, this thesis would like to use one-dimensional grating as the pattern of our periodically structured SERS substrate. Grating can modulate the amplitude and the phase of incident light, leading to the light be trapped and resonate between two gratings, and consequently contributing to the signal enhancement. We utilized E-beam lithography system with dry etching method for the fabrication of precise grating pattern. After that, a SERS substrate with different period and grating duty cycle is obtained. As a result, we chose benzoic acid as the analyte because it is the typical model of aromatic carboxylic and common preservative in food safety problem. We also demonstrated that by changing the polarization of incident laser, the SERS intensity became weak when the mode is shifted from TE to TM. Conclusively, we proposed a special designed grating account for the enhancement effect in SERS.