Study Of Surface Enhanced Raman Scattering Base On Sno₂, ZrO₂ Substrates

Surface-enhanced Raman scattering (SERS) spectroscopy with high sensitivity High selectivity, lossless explorations and adjustable point has been widely used. Scattering intensities from SERS is as 10⁵¹0¹⁴ as ordinary Raman, which can greatly improve detection limit for probe molecules. At present, the SERS active materials of SERS are mainly restricted to some precious metals (such as: Ag, Au, Cu) and transition metal (Pt, Pd, Fe, Co) and so on. And it is rarely reported that semiconductor materials can be used as the SERS substrate. As the SERS active substrate, semiconductor materials with nanoparticles have not only broadened SERS materials, but also have great significance on developing the SERS mechanism. Recently, our research group has observed SERS on different kinds of semiconductor materials (such as CdTe, Pb₃ O₄, ZnO and TiO₂), and has greatly verified charge transfer model of"semiconductor-to-molecule".Several semiconductor nanoparticles has been prepared by sol-hydrothermal method in this paper, and used as active SERS substrate and some good results emerged, and the main research achievements are showed as follow:1. The research of SnO₂ nanoparticles as SERS-active SubstrateWe have employed sol-hydrothermal method to prepare SnO₂ nanoparticles with uniform grain size. Moreover, we observed SERS phenomenon on SnO₂ nanoparticles for the first time, and has greatly verified the charge transfer model of"semiconductor -to-molecule". It shows that the charge transfer process of"Semiconductor-to -molecule"and Raman signals of adsorbed molecules largely depend on surface properties of semiconductors. There is a direct proportion relation between the surface defect degree of SnO₂ nanoparticles and their SERS activity, and with calcining temperature rising, surface defect degree reduce, then SERS activity of SnO₂ nano particles wear off. Abundant of surface properties are favourable to induce the charge transfer between SnO₂ nanometer particles and absorbed 4-MBA molecules, which leads to the increasing of SERS activities. In addition, we exciton, found that the SERS activities did not become stronger with increasing the energy of excition, but the greatest SERS activities can be obtained only at a suitable exciting energy.2. The research of SnO₂ nanoparticles doped Zn as SERS-active SubstrateAs active substrate, the increasing ability of the semiconductor nanometer materials is significantly weaker than precious metal substrate. So it is important to improve the SERS activities of semiconductor materials. As a kind of SERS active substrate with innocuity and biocompatibility, we prepare SnO₂ with a higher SERS activity. In the last chapter, we know the surface defect degree of SnO₂ nanoparticles is in direct proportion to their SERS activity, and then, to improve the SERS ability of SnO₂ nanoparticles, we changed the surface defect degree of SnO₂ nanoparticles by doped Zn, good experimental result can be obtained. The result shows that SERS ability of SnO₂ nanoparticles is becoming stronger with Zn doped increasing, and the reason is that doped Zn can improve the surface defect degree of SnO₂ nanoparticles, so it is proved again that the surface defect degree of SnO₂ plays an important role in SERS activity. We also estimate the SERS enhancement ability by increasing of SnO₂ nanometer particles doped Zn, and we calculate the enhancement factor is 1×10⁴, and that of SnO₂ without Zn doped is just 1.0×10⁴, which is obviously weaker to the doped. 3. The research of ZrO₂ nanoparticles as SERS-active SubstrateWe have prepared ZrO₂ nanoparticles with uniform grain size by a sol- hydrothermal process. We observed SERS of 4-MBA molecules on ZrO₂ nano particles. It is well known that ZrO₂ belongs to the semiconductor with wide band gap, and its band gap energy reach up to 5.0 eV. Although the band gap energy of ZrO₂ is higher than that of SnO₂ (3.6 eV), we still observed SERS activity on ZrO₂ nano particles, which illustrates that the charge transfer from semiconductor to adsorbed molecules is not from valence band of semiconductor to conduction band to adsorbed molecules, but from valence band of semiconductor to surface defect level to absor bed molecules. Generally, oxygen vacancy of ZrO₂ nanoparticles will form a oxygen vacancy energy level between valence band and conduction band, and deduce that the vacancy energy level is situated at 2.1 eV bellow conduction band. Because the band gap level of ZrO₂ nanometer particles is about 5.0 eV, oxygen vacancy energy level is situated at about 2.9 eV at the top of valence band. Oxygen vacancy energy level of ZrO₂ nanoparticles serve as the bridge in the charge transfer from semiconductor to adsorbed molecules. We also observed a rule that the Raman intensity always increase firstly, and then deccrease with rising the calcining heat of ZrO₂ nanoparticles.