Plasmonic Surface Enhanced Raman Scattering In Thin Semiconductor Films

Resonance and surface enhanced Raman (RRS & SERS) scattering are highly desirable techniques for materials study. It is experimentally not easy to observe these phenomena simultaneously due to the special experimental requirements and limited available laser wavelengths. In this study, by employing silver plasmonic nanoparticles (AgNPs) deposited on glass substrate and by in situ adjusting the band gap of thin CdS film through heat treatment, the two phenomena were observed simultaneously. The dramatically enhanced Raman scattering allowed us to in situ monitor the phase transition occurred during the heat treatment and to quantitatively characterize the fraction of the zincblende (cubic) CdS in the main base of wurtzite (hexagonal) CdS. The influence of air-annealing of CdS films on their various properties was investigated by different characterization techniques. The results suggest that the quality of CdS films remains low even after annealing, which was attributed to air-annealing and oxidation. Raman multi-phonon and the corresponding higher order scattering modes were observed due to the much enhanced surface nano-plasmonic electric field. The SERS results were compared with FDTD simulations. The simulations predicted Ramur? scattering enhancement in the CdS on AgNPs structure in agreement to the experimental results.The Low band gap CuO proves to be highly desirable candidate for energy harvesting devices among the two major phases of copper oxide (CuO and Cu2O). Copper oxide thin film was deposited on silver nanoparticles on glass substrate using sputtering method. In situ investigation was carried out by using plasmonic surface enhanced Raman scattering at different annealing temperatures. The much enhanced surface nano-plasmonic electric field made it possible to detect the presence of minor CU2O phase and monitor the phase transition at high temperature. Surface enhanced Raman spectra were also recorded at room temperature for comparison using different Raman laser wavelengths. Only the 632.8 nm laser could successfully detect the major Raman modes related to CuO and Cu2O in the film deposited on SERS-active substrate.