【作者】 崔丽；

【导师】 任斌； 田中群；

【作者基本信息】 厦门大学 ， 物理化学， 2008， 博士

【摘要】 表面增强拉曼散射（SERS）效应可以使某些纳米结构表面的吸附物种的拉曼信号强度得到极大的增强。由此使得表面增强拉曼光谱成为一种超高灵敏度的表面检测谱学技术,成功地应用于电化学和分析科学等领域。然而,SERS研究的激发线几乎集中在可见光至近红外光的波长范围,若能将激发线拓宽至紫外光区,将对SERS的应用体系拓展和复杂机理揭示做出实质性的贡献。SERS效应高低与基底的纳米结构密切相关,迄今传统的SERS基底制备方法难以在多种金属体系获得UV-SERS活性。并且,由于目前拉曼谱仪在紫外光区的性能远低于可见光区（如光通量,CCD量子收集效率,透镜收集效率等）,造成UV拉曼信号强度低,故大大限制了UV-SERS的发展。因此,本论文工作的重点是发展和优化UV-SERS活性基底,并利用UV-SERS研究一些重要体系的SERS机理。主要的创新点和成果有以下几点:（1）设计和制备具有高UV-SERS活性的纳米结构。利用电化学氧化还原循环法、纳米粒子（包括核壳结构粒子）合成法和聚苯乙烯球模板法,制备了不同的金属纳米结构,以DNA碱基腺嘌呤、SCN^-为探针分子,首次获得了Pt、Pd、Co、Ni四种Ⅷ族过渡金属体系波长325 nm的紫外光激发下的UV-SERS效应。（2）研究了Pt和Pd纳米粒子的尺寸、形状和结晶度对UV-SERS效应的影响,提出良好的结晶度是激发纳米粒子的表面等离子体共振吸收（SPR）和提高UV-SERS活性的重要前提。（3）系统研究了波长对核壳结构纳米粒子增强效应的影响。通过比较可见和紫外光激发下,Au@Pd和Au@Pt核壳结构纳米粒子的增强效应与Pd或Pt壳厚度的关系,证明了币族金属Au和过渡金属Pd或Pt在可见和紫外光区具有不同的增强效应。可见光激发下,Au核对增强起主要贡献,而在紫外光激发下,增强的贡献皆来自于Pd或Pt壳。（4）具有可调SPR吸收且大面积形貌均匀的过渡金属纳米碗阵列的制备和UV-SERS研究。利用聚苯乙烯球模板法,电沉积了直径D在200 nm至900 nm、厚度在0.1 D-1.2 D范围内变化的纳米碗阵列。以腺嘌呤为探针分子,首次获得了Pt和Pd纳米碗的UV-SERS。UV-SERS增强效应与纳米碗的大小和深度密切相关,其中聚苯乙烯球直径200 nm,沉积厚度0.3 D的Pd纳米碗表现出最好的UV-SERS增强效应。（5） UV-SERS的电磁场增强机理研究。利用紫外-可见（反射）吸收谱研究了Pt和Pd纳米粒子和纳米碗的吸收特征,首次从实验上证实了Pt和Pd在紫外区有SPR吸收。通过对比分析UV-SERS信号强度与SPR吸收特征,发现两者之间存在较好的匹配关系,证明电磁场增强机理对Pt和Pd纳米结构的UV-SERS效应具有重要作用。（6）系统研究了腺嘌呤/金属体系的增强机理。通过改变激发光波长（325 nm、514.5 nm和632.8 nm）和电极电位,研究了腺嘌呤吸附在Rh和Pd电极上的电荷转移增强（CT）机理。观察到波长为325 nm的紫外激光所引起峰值电位的明显位移,以及峰值电位与激发光能量之间具有斜率为正的线性关系,说明CT机理对增强有贡献且电荷转移方向是从金属到分子。这一结果对理解腺嘌呤在Au或Ag的单分子SERS和TERS的巨大增强效应,具有重要的启示作用。另外,推断出该体系共存电荷转移增强、共振增强和电磁场增强三种增强作用。（7）利用SERS研究了电化学共吸附和表面取向问题。详细研究了质子化DNA碱基与ClO₄^-在金纳米粒子上的共吸附行为和质子化碱基间的氢键作用;观察到电极表面的吸附氢和氧对吡嗪在铑上取向改变具有较大影响,电位和浓度变化皆会引起的吸附取向的改变。综上所述,本论文工作成功地将UV-SERS拓宽到Pt、Pd、Co和Ni四种过渡金属体系,研究了表面等离子体共振吸收对过渡金属UV-SERS的重要贡献,并结合UV-SERS和Vis-SERS对腺嘌呤/Rh（Pd）体系的增强机理进行了系统研究,促进了UV-SERS研究的进展。最后应指出,如果拉曼谱仪及相关光学元件（如CCD收集效率、谱仪的光通量等）在紫外光区的性能能够达到目前可见光区的水平,对于同样的分子/金属体系,UV-SERS的信号甚至要强于Vis-SERS。这预示着UV-SERS还有很大的发展潜力,随着拉曼谱仪和各种光学元件在紫外光区性能的改进,以及制备具有更高UV-SERS活性的纳米结构,UV-SERS以及UV-SERRS将在不远的将来得到广泛应用。更多还原

【Abstract】 Surface-enhanced Raman scattering can extremely enhance the Raman signal of species adsorbed on the surface of nanostructures,which makes surface-enhanced Raman spectroscopy（SERS） be a very sensitive tool for the detection of surface species,and thus widely used in many fields like electrochemistry and analytical chemistry.However,the excitation lines used in SERS studies almost always focus on the visible to near infrared region.If it can be extended to the UV region,the use of UV excitation will expand the SERS application and provide new insights and experimental data to discover the complicated SERS mechanisms.SERS enhancements greatly depend on the nanostructure of SERS substrates. Presently,the traditional methods for fabricating SERS substrates are still difficult to obtain UV-SERS active substrates on various metals.In addition,the performance of Raman spectrometer in UV region is much worse than that in visible region,like the throughput,quantum efficiency of CCD and collection efficiency of objectives,which results in a much lower SERS intensity in UV region than that in visible region.The above two facts greatly restrict the development of UV-SERS studies.Therefore,the objective of this dissertation is to develop and optimize UV-SERS active substrates by using several novel nanostructure fabrication methods,and employ UV-SERS to study the enhancement mechanism of some important molecule/metal systems.The main results in this thesis are listed as below:（1） Design and fabrication of various nanostructures with high UV-SERS activity.The methods of electrochemical oxidation reduction cycle（ORC）,synthesis of nanoparticles （including core-shell nanoparticles） and electrodeposition of nanovoids through polystyrene sphere templates were employed to prepare diverse metallic nanostructures. By using adenine and SCN^- as the probe molecules,for the first time,UV-SERS excited with a 325 nm UV laser was obtained on four metals inⅧgroup,i.e.Pt,Pd,Co and Ni.（2） Study of the effect of size,shape and crystallinity of Pt and Pd nanoparticles on the UV-SERS enhancements.It reveals that the nanocrystals with good crystallinity are favorable for the excitation of surface plasmon resonance and the improvement of UV-SERS activity.（3） Study of the wavelength effect on the SERS enhancements of core-shell nanoparticles.By comparing the intensity-shell thickness profile of Au@Pt and Au@Pd core-shell nanoparticles excited with the UV and visible lasers,it was proved that coinage metal（Au） and transition metal（Pt or Pd） had very different enhancements in UV and visible region.In visible region,Au core plays a dominant role in the SERS enhancement, but in UV region,the UV-SERS enhancements are solely contributed by Pt or Pd shell.（4） Fabrication and UV-SERS study on Pd and Pt nanovoids with tunable SPR absorption and uniform morphology.Electrodeposition through a range of close packed arrays of polystyrene sphere templates was employed to produce a series of palladium and platinum nanovoids with different thicknesses.The diameter（D） of spheres used as the template varies from 200 nm to 800 nm and the thickness of nanovoids varies from 0.1 D to 1.2 D.For the first time,the application of these substrates for UV-SERS was demonstrated,using adenine as the probe molecule,under electrochemical potential control. UV-SERS enhancement of palladium and platinum nanocavities was found to be both void diameter and film thickness dependent,and the Pd nanovoids with the thickness of 0.3 D templated by 200 nm diameter sphere show the best UV-SERS activity.（5） Study of the electromagnetic field enhancement mechanism of UV-SERS on Pt and Pd.The surface plasmon resonance（SPR） in UV region was obtained for the first time on Pt and Pd nanoparticles and nanovoids via UV-Vis absorption and normal incidence reflectance measurements.The SPR correlates well with the UV-SERS enhancement, demonstrating that electromagnetic field enhancement plays an important role in the UV-SERS enhancement of Pt and Pd nanostructures.（6） Study of the charge transfer enhancement mechanism of adenine/metal systems. The charge transfer（CT） enhancement mechanism of adenine adsorbed on Rh and Pd was studied by changing either excitation energy（hv） or Fermi level which can be easily tuned by changing the applied potential.The obvious shift of E_max（potential at which intensity reach the maximum） with the excitation energy,and the linear relationship between hv and E_max,convincingly demonstrate the existence of CT enhancement and the charge transfer direction is from the metal to adenine molecules.This result is very important for the understanding of the huge enhancement observed in SM-SERS or TERS spectra of adenine adsorbed on Ag or Au.Finally,it was deduced that there were totally three enhancement mechanisms in adenine/Rh and adenine/Pd systems,i.e.charge transfer,pre-resonance Raman effect and electromagnetic field.（7） Study of the electrochemical coadsorption and adsorption orientation by SERS. The coadsorption behavior of protonated DNA bases with ClO₄^- and the detection of hydrogen bonds between protonated DNA bases were studied detailedly by SERS;the adsorption orientation of pyrazine on Rh was observed to change both with the applied potentials and the solution concentration,moreover,the coadsorbed O and H were proved to have great influence on its orientation.In summary,the present thesis successfully extended UV-SERS to four important transition metals,i.e.Pt,Pd,Co and Ni,and further studied the important role of EM （electromagnetic field） mechanism in the UV-SERS enhancement of nanostructures. Moreover,charge transfer enhancement of adenine/Rh（Pd） systems was also systematically studied by UV and visible laser excited SERS.This work greatly promotes the UV-SERS studies.Finally,what should be specially mentioned here is that UV-SERS intensity will be stronger than that of Vis-SERS provided that optical elements used in UV region can perform as well as those used in visible region.This predicts the great potential of UV-SERS.With the improvement of the performance of Raman spectrometer and optical elements in UV region,together with the fabrication of nanostructures with higher UV-SERS activity,UV-SERS and UV-SERRS will get extensively applications in the near future.更多还原