【作者】 纪南；

【导师】 赵冰；

【作者基本信息】 吉林大学 ， 物理化学， 2010， 博士

【摘要】 本论文针对目前表面增强拉曼散射(SERS)技术在应用中所面临的主要问题,即缺乏高活性、高稳定性和均匀性的SERS活性基底,利用高度有序的多孔阳极氧化铝膜(AAO)作为模板,制备具有优异性能的SERS活性基底;另外,在我们课题组关于半导体纳米材料SERS效应的研究基础上,合成氧化锌/银纳米复合物,研究半导体材料的复合对银的SERS效应的影响,取得了一些创新性成果,具体内容如下:(1)采用两步阳极氧化法制备了具有规则结构的多孔阳极氧化铝模板,对电化学抛光过程以及阳极氧化过程进行了电流随时间变化的监测,优化抛光条件,研究了阳极氧化过程。对制备的阳极氧化铝模板的细微结构进行详细研究,SEM表征发现这种方法所制备的模板表面呈现规则的凸起结构。(2)利用多孔氧化铝模板制备过程中得到的铝模板,采用磁控溅射方法,将铝模板的结构复制到溅射的银膜表面,得到超稳定性、具有极高抗氧化能力的SERS基底,对其结构进行了详细研究。研究吸附分子对这种有序结构的局域表面等离子体共振(LSPR)最大吸收峰的影响,SERS测试表明这种基底具有巨大的应用前景。(3)利用制备的多孔氧化铝模板,采用交流电化学沉积方法,将银纳米粒子填充到模板的孔道当中,得到具有三维结构的基底。SERS测试表明该基底具有较高的SERS增强能力,同时具有良好的均匀性、重复性以及稳定性;紫外-可见反射光谱可用来测定AAO膜的厚度,在沉积银之后的AAO模板的反射光谱中出现了干涉增强现象,这是由于银的LSPR所引起的。(4)制备了氧化锌/银纳米复合物,分析其形成机理;详细对比了单纯氧化锌与氧化锌/银纳米复合物的紫外-可见吸收光谱、荧光光谱和SERS光谱的变化,认为这些变化是由于银纳米粒子与氧化锌之间的电子转移引起的。更多还原

【Abstract】 Surface-enhanced Raman scattering (SERS) spectroscopy is a powerful analytical tool for chemical and biological sensing applications due to its advantages of super-sensitivity and wealth of structural information on characteristic“fingerprint”signatures of analytes. But there are still some problems that block SERS to be a universal analytical tool, especially on quantitative analysis. One of the most important problems is the poor performance of SERS substrates. SERS is an optical phenomenon which is closely related with the substrates absorbing molecules and SERS signals are strongly dependent on the feature of substrates. Since the discovery of SERS, kinds of SERS substrates were prepared, including metal colloids, metal island films, ordered arrays, metal-metal or metal-semiconductor composite materials, and so on. Some of these substrates have shown great potential, but there is still some way to go, compared with ideal SERS substrates. Usually, an ideal SERS substrate suitable for quantitative analysis should possess advantages of high sensitivity, homogeneity, stability and purity. Making SERS substrates to satisfy these conditions as much as possible is the key of promoting SERS to be a reliable analytical tool. In the thesis, porous Anodic Aluminum Oxide (AAO) films with regular structure were used as templates to fabricate two-dimensional (2D) and there dimensional (3D) SERS substrates, and then the properties of these substrates were tested. The major contributions of this work are as follows: (1) Preparation of AAO templates and detail characterization on microstructureAAO templates with regular structure were prepared using a two-step anodization approach. During the electrochemical polishing process, changes of current with time were monitored. Electrochemical polishing was performed under 15V, 17V and 19V, respectively. AFM was performed to characterize polishing effect and results indicate that 17V is the most suitable for our preparation process. Changes of current with time were also monitored during anodization approach and step-step voltage decrement process. Anodization approach could be divided into three stages, including the formation of barrier, pore formation and stable growth process. In the step-step voltage decrement process, the thinning rate of barrier layer in each voltage range was different. Microstructure of anodic aluminum oxide templates before and after widening pores in phosphoric acid was investigated by AFM and SEM in detail. The top face of AAO templates takes on regularly convex structure, which is resulted from the uneven distribution of surface electric field. But after widening pores, the convex structure was disappeared due to corrosion.(2) Preparation of ultrastable 2D SERS substrates using AAO templatesThe aluminum substrate remained after the process of oxidation acted as the template to prepare SERS substrate. A layer of silver film was formed on aluminum substrate using magnetron sputtering method. Aluminum substrate was then peeled off and a layer of silver was obtained. The morphology of SERS substrate and aluminum substrates were studied in detail by AFM and SEM. Results show that the silver films replicated the structure of aluminum substrates perfectly, which took on ordered array of Ag spherical caps. Throughout the preparation process, the aluminum substrate not only acted as the patterned matrix, but also served as a coating that protected Ag from being oxidized. UV-vis reflection measurement was performed to monitor the adsorption process of probing molecules. Taking 4-mercaptopyridine as probing molecules, SERS spectra were investigated. Comparing with the ordinary Ag film, the patterned Ag layer exhibited better SERS activity. The ultrastability and regular nanostructure endow these substrates with great potential in SERS applications.(3) Preparation of 3D SERS substrates using AAO templatesHighly ordered porous AAO templates were employed to construct SERS substrates. An alternating current (AC) electrochemical deposition was used to fill AAO templates with Ag nanoparticles. SEM characterization indicated that Ag nanoparticles were 10-20 nm in size and there were some short Ag nanowires. Taking 4-mercaptopyridine as probing molecules, SERS measurement was performed on substrates deposited for 30, 60, 120 and 180 s, respectively. High-quality SERS spectra were observed. The UV-vis mirror reflection spectra were measured to investigate the localized surface plasma resonance (LSPR) absorbance. An interesting phenomenon of LSPR-affected thin film interference was observed. SERS mapping was performed to characterize the homogeneity of as-prepared substrates. Good homogeneity and stability make these substrates good candidates for SERS spectroscopy.(4) Preparation and optical properties of ZnO/Ag nanocompositesAt present, neither electromagnetic enhancement mechanism nor chemical enhancement mechanism could make a full explanation of SERS, which is closely related to the complex experimental conditions and also related to theoretical models and theoretical methods. Until now, there is not yet a unified theory to explain the underlying physical and chemical nature of SERS. Electromagnetic mechanism has long been considered to play the most important role in SERS enhancement, but in recent years, research on chemical enhancement mechanism proved that the chemical charge transfer mechanism play a major role in SERS enhancement of semiconductors. An enhancement of 104 was observed. These experiments conducted in semiconductors exclude interference of electromagnetic field and have great significance for understanding the nature of SERS. However, in most system, electromagnetic mechanism cannot be completely ruled out, so the further study of metal-semiconductor composite is very helpful for investigating the relationship between electromagnetic mechanism and chemical mechanism in complex systems. We prepare ZnO/Ag nanocomposites by trisodium citrate-reduction in light conditions. SEM characterization indicated that silver nanoparticles were found only in parts of the surface sites of ZnO and there were no independent silver particles. These indicated that ZnO induced sodium citrate to reduce silver nitrate. In UV-vis absorption spectra, the plasma band of Ag in ZnO/Ag nanocomposites red shifted and widened compared with the silver colloid. This is due to the electron transfer from Ag to ZnO. In photoluminescence spectra, UV emission of ZnO due to exciton recombination increased compared to pure ZnO under the same concentration. This is also resulted from the electron transfer from Ag to ZnO. In SERS spectra, enhancement of the individual b2 vibration mode is due to electron transfer.更多还原