Study Of Surface Enhanced Raman Scattering Base On ZnO Substrates

The mechanism of SERS is not clear and this has serious impact on its applications. Therefore, the study for SERS mechanism becomes the difficulty and emphases in the SERS study area in the current. The study for the physical mechanism of SERS is quite mature, but for the chemical mechanism, more studies are still theoretical study. The experimental data are not enough to support the theory and more results are still in the speculation stage. So the existence of chemical mechanism and the influence degree on SERS have not obtained the consensus.Our group has observed the SERS phenomenon on many semiconductor nanoparticles such as ZnO, PbO, PbO2,CuO, CdTe and Pb3O4 after several years'works. This observation extends the SERS substrate materials from metal to semiconductor area. Because the semiconductor surface plasmon resnonance is away from the excitation light band, using semiconductor as the SERS substrate can greatly reduce the physical enhance influence. At the same time, it can enlarge the chemical enhance effect and this is very meaningful for the study of chemical mechanism in SERS.Based on the current research of chemical mechanism in SERS, this paper has done some useful work in these aspects and obtained some innovative results, and its main contents are summarized as follows: 1. We have prepared different size of ZnO nanoparticles and studied the Raman effect of different size ZnO to the corresponding adsorbed molecules. With the change of nanoparticles crystallite size, the relative intensity of Raman spectroscopy has not changed, but the absolute intensity has increased first and then sharp decreased. We interpret this effect as due to formation of a charge-transfer complex between a surface-bound exciton and the adsorbed molecule. 2. ZnO nanorods / PATP / Ag sandwich structure were fabricated with ZnO and silver nanoparticles and functional molecules through layer-by-layer self-assembly techniques. Under the near-IR excitation (1064 nm) that is far away from the SPR of the nanoparticles in the assemblies, the enhancement in surface-enhanced Raman spectra from the CT mechanism can be relatively amplified. The larger enhancement of the b2 modes, relative to that of the a1 modes, is ascribed to the charge transfer between the silver nanoparticles and ZnO tunneling through the interconnecting PATP molecules. The result of experiment for the first time demonstrated that directional charge transfer between metal and semiconductor tunneling through the interconnecting molecules contribute to the overall SERS enhancement. 3. We have observed the single molecular layer adsorbed 4-MPY Raman spectra on the hourglass-type ZnO single crystal surface. On the different crystal face, the observed Raman signal intensity is different, and on the same crystal face, the Raman signal intensity is also different when at different locations.Moreover, we have prepared dendritic Ag using aluminum as the reductant and studied its SERS effect.