Development And Application Of Surface-enhanced Spectroscopy With A Metal Nanofilm

The unique optical properties of metallic nanoparticle films enable the enhancement of infrared absorption of ad-molecules,producing the so-called surface-enhanced IR absorption(SEIRA) effect.Spectroscopy based on this effect,i.e.,surface-enhanced infrared absorption spectroscopy(SEIRAS) is a powerful investigating tool for surface and interface analysis at molecular level,not only for trace analysis at solid-gas interfaces in ambient environment but also for sensitive characterization of adsorption and reaction at electrochemical solid-liquid interfaces.First,surface-enhanced infrared absorption spectroscopy(SEIRAS) and surface-enhanced Raman scattering spectroscopy(SERS) are two complementary spectroscopic techniques,and more comprehensive surface information can be obtained by combining these two techniques.Ag is one of the most important metals used in SEIRAS and SERS analysis.It is essential to develop an economic and facile approach to fabricate both a SEIRA and SERS -active Ag substrate for its application in surface trace analysis in ambient environment.Hence,the first part of this thesis aims to seek suitable conditions for fabricating a Ag nanofilm on Si as the substrate for SERS and SEIRAS analysis.The oxidization of methanol on Pt electrode is an important system in electro-catalysis.It was believed that the participation of neighboring Pt atoms is a must. In part 2 of this thesis,a CN^--modified Pt electrode was used to limit the number of open Pt atoms accessible for methanol oxidation,and ATR-SEIRAS was utilized to investigate the behavior and mechanism of methanol electro-oxidization.Third,the SEIRA effect of metal nanofilms depends on particle sizes and shapes.Herein,Au nanoparticles with different sizes and shapes were synthesized and assembled,for potential application to SEIRAS in the near future.In addition,self-assembly and seeded growth tactics were applied to deposit continuous Au layer on the inner-wall of capillary for potential application in flow analysis.Main achievements of this thesis are summarized as follows:A facile and economic tactics to fabricate and immobilize silver nanoparticles on a thin Si wafer(AgNP/Si) is proposed and achieved as a "template" for SEIRAS and SERS analysis in ambient environment.The protocol involves immersion of the pretreated Si wafer in a solution containing silver nitrate and hydrofluoric acid.To screen appropriate conditions of preparing AgNP/Si for SEIRAS application,different combinations of AgNO₃ and HF concentrations were examined with para-nitrobenzoic acid(PNBA) used as the probe molecule in transmission measurements,with a maximum enhancement factor of ca.600 achieved.These SEIRA-active templates were also promising for SERS application,as demonstrated with high quality SERS spectra obtained respectively for iron(Ⅲ) protoporphyrin and para-mercaptobenzoic acid(PMBA) adlayers on AgNP/Si with the excitation line of 632.8 nm.This approach may be extended for making SEIRA and SERS-active Au and Cu nanofilms on Si.In-situ ATR-SEIRAS was applied to investigate the process of methanol electro-oxidation on a CN^--modified Pt electrode with preferential(111) orientation where the reactive sites on Pt was partly blocked by CN^-.A coverage of 0.5 of CN^-adlayer on Pt decreased the rate of methanol electro-oxidization by an order of magnitude. Nevertheless,the dual-path mechanism,i.e.,via CO indirect path and via HCOO^- direct path,remained essentially unchanged on this surface.Preliminary study on the controlled synthesis of gold nanorods and their self-assembly on infrared-active window has been carried out.Au seeds were prepared by the reduction of HAuCl₄ by NaBH₄,and grown in a solution containing CTAB to Au nanorods.Different aspect ratios can be tuned by varying the proportion of seeds and Au³⁺ in the solution.Electrostatic attraction of Au nanorods to SiO₂/Si substrates with and without MPTMS interlayer yielded different surface coverages of Au nanorods.AFM characterization showed that nanorods did not change their shapes upon adsorption,no aggregation was observed.Self assembly and seeded growth tactics were utilized to deposit conductive and thickness-tunable Au layers in the inner wall of capillary,providing a convenient and economic way for metallization inside capillaries of various shapes and size.