Preparation, Study Of ZnO Semiconductor Nanomaterials And Composites As Enhanced Raman Scattering Substrates

Surface Enhanced Raman Scattering has been considered as a powerfully analytical tool for sensitive and selective molecular identification on rough surfaces. Previous study demonstrated that rough surfaces have been essentially restricted to the surfaces of noble and transitional metal. This research will extend the enhanced Raman scattering effect from metal to semiconductor fields. Semiconductor nanostructures are currently regarded as potential building blocks for nanodevices. The performance and reliability of these devices strongly rely on the surface and interfacial properties of the constituent nanomaterials. Metal-semiconductor nanocomposites have been given great attention in the several years. There are many papers and patents mainly concerning methods of preparation and study of optical properties. Because this novel nanomaterails may contain both properties of metal and semiconductor, such as optical, electrical and magnetic properties, which indicates that they could have new different function and application. Thus, this study points to the very promising future of using enhanced Raman spectroscopy for understanding surface properties of semiconductor, chemisorptions and reactions mechanism of molecules in some practical systems. This work focuses on studying ZnO nanomaterials and its nanocomposite with metal as enhanced Raman scattering substrates. Our research is listed as follows:Firstly, we prepared ZnO nanoarrays on cleaned Si substrate. And then ZnO nanoarrays are functionalized through Self-assembly method. At last, we obtained ZnO/4-Mpy/Ag assembly by immersing the functionalized ZnO nanoarrays into Ag colloids for 30 minutes. Raman spectroscopy and XPS are employed to characterize this process, and the micro-structure of the assembly is obtained from these results. After comparing with the Raman spectra obtained from ZnO/4-Mpy/Ag and from ZnO, we safely asserted that the structure of ZnO/4-Mpy/Ag is different from the named sandwich, but Ag nanoparticles directly interact with the S atom of 4-Mpy which adsorbed on the surface of ZnO arrays. The Raman spectrum from ZnO/4-Mpy/Ag assembly is not equal to the simple result of the spectrum from Ag nanoparticles increased by that from ZnO nanarrays. The cooperative effect between ZnO and Ag attributes to the enhanced Raman scattering of 4-Mpy, and the effect of EM from Ag nanoparticles is more significant. At the same time, the result of XPS demonstrates the conclusion again.In order to understand the enhanced Raman scattering of ZnO nanomaterials, we directly synthesized Ag/ZnO nanocomposite with diverse Ag contents in water bath. SEM and XRD are employed to characterize the morphology and structure of these nanocomposites. The result showed that Ag nanoparticles had ver little or no effcet on the morphology and size of Ag/ZnO nanocomosites which were nanorods. Then we mainly discussed the enhanced Raman scattering of Ag/ZnO and the effect of Ag contents to SERS of ligand molecule adsorbed on the surface of Ag/ZnO. The enhanced mechanism here is analyzed simply. When visible light is incident on the metal surface, there will generate a strong local electromagnetic field at the interface between ZnO and Ag, leading to the enhancement of vibration of ligand molecule. Additionally, Ag/ZnO nanorods is used as enhanced Raman scattering substrates, and the SERS of 4-Mpy adsorbed on the surface of Ag/ZnO is discussed. Addtionally, the result indicated that, when there is same concentration of probe molecule adsorbed on Ag/ZnO nanocomposites and ZnO nanorods, the Enhanced Raman Scattering from the former will be better than that from the later.Finally, Ag/ZnO nanocrystals are synthesized through ultrasonic method. We use several methods, namely, SEM, XRD, XPS, and UV, to obtain the information concerning the morphology and structure of Ag/ZnO. The result showed that the obtained Ag/ZnO nanocomposites didn`t form Core-Shell structure, but most of Ag nanoparticles separately deposited on the surface of ZnO nanocrystals, namely a heterogeneous nanostructure. The absorption due to Ag nanoparticles was not apparent in the the absorption spectra of Ag/ZnO nanocomposites. It may be arised from the small size of the Ag nanoparticles or the low Ag/ZnO ratio in the composites, causing the absorption by the Ag nanoparticles to be overshadowed by the more prominent ZnO absorption. Then the behavior of BVPP adsorbed on these nanocrystals is mainly discussed by Raman spectroscopy. Comparing with the Raman spectra from Ag and ZnO, which from Ag/ZnO has its own characteristics, different from either of them. BVPP molecule on Ag/ZnO nanocomposites shared similar absorption behavior with that on Ag nanoparticles. Probe olecule chemically adsorbed on the surface of Ag/ZnO nanocomposites through forming Ag-N bond, and perhaps were perpendicular to substrates. Comparing with the Raman spectrum from Ag nanoparticles, the Raman spectrum from Ag/ZnO nanocomposites existed many differences, such as the HFMW, frequencies and relative intensity of bands. Although the Raman spectrum from nanocomposites was different with that from ZnO nanocrystals, there were some same factors. For example, both of them appeared evident virbational band at 1196 cm-1.Therefore, Ag/ZnO nanocrystals could be considered as new SERS substrates, having better enhanced ability than ZnO nanocrystals. Futhermore, it demonstrated that the Enhanced Raman Effect of probe molecule depends on the nature of substrates.In all, this work is very significant. Because it not only benefits to apply Raman spectroscopy to the study of the interface between metal and semiconductor, but also contributes to understanding the nature of enhanced Raman scattering of organic molecule adsorbed on the surface of metal-semiconductor...