Time development of sers from pyridine,pyrimidine, pyrazine,and cyanide adsorbed on ag electrodes during an oxidation-reduction cycle

The time development of surface enhanced Raman scattering (SF.RS) from pyridinc, pyrimidine, pyrazine, and cyanide adsorbed on Ag electrodes has been recorded during an oxidation-reduction cycle by using an optical multichannel analyzer. The OMA system, capable of detecting spectra over a range of 400 cm^?1 in 25 ms, was employed to monitor changes in Raman intensities, frequency shifts, and linewidths. Whereas measurements on pyridine confirm previously reported results and resolve some controversial questions, results on pyrazine provide new insight into the SERS mechanism. Because of the inversion symmetry of pyrazine, the Raman and infrared active modes are separated, but no significant distinction is observed in the SERS time development of Raman active compared to infrared active modes. In SERS from cyanide, large changes in the C - N stretching frequency have been observed.     

Surface-enhanced Raman scattering (SERS) activity of Ag, Au and Cu nanoclusters on TiO2-nanotubes/Ti substrate

Tubular arrays of TiO₂ nanotubes (ranging in diameter from 40 to 110 nm) on a Ti substrate were used as a support for Ag, Au or Cu deposits obtained by the sputter deposition technique, where the amount of metal varied from 0.01 to 0.2 mg/cm². Those composite supports were intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured at different cathodic potentials ranging from −0.2 down to −1.2 V after the pyridine had been adsorbed on the metal-covered TiO₂ nanotube/Ti substrates. In addition, SERS spectra on a bulk standard activated Ag, Au and Cu substrates were also measured. The SERS activity of the composite samples was strongly dependent on the amount of metal deposit, e.g. at and above 0.06 mg Ag/cm², the intensity of SERS signal was even higher than that for the Ag reference substrate. The high activity of these composites is mainly a result of their specific morphology. The high SERS sensitivity on the surface morphology of the substrate made it possible to monitor very small temporal changes in the Ag metal clusters. This rearrangement was not detectable with microscopic (SEM) or microanalytical (AES) methods. The SERS activity of Au or Cu clusters was distinctly lower than those of Ag. The spectral differences exhibited by the three kinds of composites as compared to the reference metal samples are discussed.     

Identification of species formed after pyridine adsorption on iron,cobalt, nickel and silver electrodes by SERS and theoretical calculations

The adsorption of pyridine (py) on Fe, Co, Ni and Ag electrodes was studied using surface‐enhanced Raman scattering (SERS) to gain insight into the nature of the adsorbed species. The wavenumber values and relative intensities of the SERS bands were compared to the normal Raman spectrum of the chemically prepared transition metal complexes. Raman spectra of model clusters M₄(py) (four metal atoms bonded to one py moiety) and M₄(α‐pyridil) where M = Ag, Fe, Co or Ni were calculated by density functional theory (DFT) and used to interpret the experimental SERS results. The similarity of the calculated M₄(py) spectra with the experimental SERS spectra confirm the molecular adsorption of py on the surface of the metallic electrodes. All these results exclude the formation of adsorbed α‐pyridil species, as suggested previously. Copyright © 2009 John Wiley & Sons, Ltd.     

In situ spectroelectrochemical surface-enhanced Raman scattering (SERS) investigations on composite Ag/TiO2-nanotubes/Ti substrates

A tubular array of TiO₂-nanotubes on a Ti substrate was used as a support for an Ag sputter-deposited layer intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples of Ag/TiO₂-nanotube/Ti were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured at different cathodic potentials ranging from −0.2 down to −1.2 V after the pyridine had been adsorbed on the TiO₂-nanotube/Ti substrates covered with the Ag deposit. In addition, SERS spectra on a bulk electrochemically-roughened Ag reference substrate, were also measured.The SERS activity of the composite samples was strongly dependent on the amount of Ag deposit and, in some cases, was even higher than that for the Ag reference substrate. The SERS intensity vs. electrode potential dependences measured were interpreted in terms of the modified electronic structure of the Ag deposits due to the interaction of the Ag clusters with the TiO₂-nanotube/Ti substrate.     

SERS谱峰强度对电位阶跃的响应速率

ＳＥＲＳ谱峰强度对电位阶跃的响应速率顾仁敖，吴芸，乔专虹，姚建林（苏州大学化学系苏州２１５００６）田中群，李五湖（厦门大学化学系厦门３６１００５）ＴｈｅＲｅｓｐｏｎｓｅＲａｔｅｏｆＴｈｅＳＥＲＳＩｎｔｅｎｓｉｔｙＷｈｅｎＡＰｏｔｅｎｔｉａｌＳｔｅｐｉ...     

银纳米颗粒阵列的表面增强拉曼散射效应研究

利用具有高密度拉曼热点的金属纳米结构作为表面增强拉曼散射(SERS)基底,可以显著增强吸附分子的拉曼信号.本文通过阳极氧化铝模板辅助电化学法沉积制备了高密度银(Ag)纳米颗粒阵列;利用扫描电子显微镜和反射谱表征了样品的结构形貌和表面等离激元特性;用1, 4-苯二硫醇(1, 4-BDT)为拉曼探针分子,研究了Ag纳米颗粒阵列的SERS效应.通过优化沉积时间,制备出高SERS探测灵敏度的Ag纳米颗粒阵列,检测极限可达10~(-13)mol/L;时域有限差分法模拟结果证实了纳米颗粒间存在强的等离激元耦合作用,且发现纳米颗粒底端的局域场增强更大.研究结果表明Ag纳米颗粒阵列可作为高效的SERS基底.     

The role of surface electronic states in surface enhanced raman scattering

The dependence of the surface enchanced Raman scattering (SERS) intensity on the electrode potential is considered in terms of the nonresonant adiabatic charge-transfer mechanism. Surface electronic states of a substrate metal are proposed to be responsible for the observed potential dependence of the SERS signal. The contribution of surface states to the nonlinear metal polarizability was found from electroreflectance spectra of silver single-crystals. Good agreement between the measured and calculated potential behaviour of the SERS signal was found for pyridine absorbed on the silver electrode.     

Raman investigations of TiO2 nanotube substrates covered with thin Ag or Cu deposits

A tubular array of TiO₂ nanotubes on Ti matrix was used as a support for Ag or Cu sputter‐deposited layers intended for surface‐enhanced Raman scattering (SERS) investigations. The composite samples of Ag/TiO₂–nanotube/Ti and Cu/TiO₂–nanotube/Ti were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) [and scanning Auger microscopy (SAM)] to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured after it had been adsorbed on the TiO₂–nanotube/Ti substrates covered with thin Ag or Cu deposit as well as on the bulk electrochemically roughened Ag or Cu reference substrates. It was found that the SERS spectra measured for pyridine adsorbed on the bulk silver substrate were significantly different than the spectra measured on the TiO₂–nanotube/Ti substrates covered the Ag layer. The spectra measured for pyridine adsorbed on the Ag/TiO₂–nanotube/Ti suggest that on the surface of such a composite substrate there are many Lewis acidic sites. Spectra typical for pyridine adsorbed on acidic sites were observed even after deposition of a relatively thick silver layer (e.g. an Ag layer with an average thickness of 80 nm) on the TiO₂–nanotube/Ti support. Our findings suggest that TiO₂–nanotube/Ti support is a promising substrate for the preparation of metallic nano‐clusters on a support containing acidic active sites. Copyright © 2009 John Wiley & Sons, Ltd.     

Silver‐decorated carbon nanotube networks as SERS substrates

We report on investigations upon a surface‐enhanced Raman scattering (SERS) substrate produced from a two‐dimensional single‐walled carbon nanotube (SWNT) network decorated with Ag nanoparticles. Using the strong and unique Raman spectrum of SWNTs as a reference, the SWNT/Ag nanostructure can be considered to provide two regions: one with an ultrasensitive SERS response for single‐molecule SERS (SMSERS) study; and another with uniform SERS enhancement over an area of several square millimeters for general SERS measurements. We report the appearance of an anomalous Raman feature at around 2180 cm⁻¹ in the high‐sensitivity region which exhibits the characteristics of SMSERS. The SERS performance of the uniform area was characterized using pyridine vapor adsorbed onto the substrate. The presence of the SWNT/Ag nanostructure enhanced the Raman intensity by over seven orders of magnitude, a factor comparable to or exceeding that obtained on SERS substrates reported by other groups. The results indicate great potential to produce highly sensitive, uniform SERS substrates via further fine‐tuning of the nanostructure. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface enhanced Raman scattering of water on an Ag electrode

Surface enhanced Raman scattering of adsorbates on an Ag electrode in various electrolytes (e.g., 0.1–1.0 M KF, KCl, KBr, KI, K₃PO₄, and NaN₃) has been investigated in an effort to elucidate the mechanism of the enhancement of water compared to that for other adsorbates. (It is well known, for example, that pyridine exhibits large enhancement in 0.1 M KCl while SERS from water is not detectable unless the salt concentration is raised to almost 1 M.) Use of an optical multichannel analyzer allowed rapid recording of Raman spectra, and SERS intensities of adsorbates could therefore be monitored simultaneously during a continuous oxidation-reduction cycle. Potential dependencies of SERS intensities when the electrode potential is cycled in a non-faradiac potential range immediately following oxidation and reduction indicate that adatoms are partially responsible for the Raman enhancement. Furthermore, the anions in the electrolyte play an important role in stabilizing these “active sites.” For this reason, the degree of enhancement is influenced by the solubility of the Ag compound formed during oxidation and the specific adsorption of the anions to the Ag surface. Preferential alignment of H₂O molecules with their oxygen ends facing the surface at positive potentials, the tendency of anions in the electrolyte to disrupt hydrogen bonding with the water network, and the weak hydrogen bonding of H₂O with the anions give rise to a SERS lineshape from adsorbed H₂O molecules which is narrower than, and thus distinguishable from, the Raman line of bulk water. Thus, the degree to which the particular anions in the electrolyte disrupt hydrogen bonding among water molecules and reform hydrogen bonding between the anions and H₂O molecules influences the SERS lineshape and the apparent enhancement of the H₂ Raman emission.     

Irreversible loss of adatoms on Ag electrodes during potential cycling determined from surface enhanced raman intensities

Surface enhanced Raman scattering of adsorbates (Ag⁰-Cl^?, H₂O and pyridine) on Ag electrodes in 1M KC1 and 1M KCl+0.05M pyridine electrolytes was monitored continuously with an optical multichannel analyzer system as the electrode potential was cycled over various ranges within nonfaradaic regions of the oxidation-reduction cycle. A systematic investigation was performed of the potential dependence of SERS of pyridine in 1M KX + 0.05M pyridine electrolytes, where X = F, Cl, Br and I. Since the surface coverage of the adsorbates is reversible with potential cycling within a potential range, it was possible to determine potential dependences of the irreversible loss in the SERS enhancement factor which occurs as the electrode potential is ramped toward the potential of zero charge (PZC). The results provide strong support for the role of adatoms on the electrode surface in the overall enhancement mechanism. There is evidence that the strongly bound adsorbates immobilize the adatoms at positive potentials but allow the adatoms to migrate and become lost at surface defects as the potential approaches the PZC where the adsorbates are less tightly bound.     

金银/氮化钛表面增强拉曼基底制备及对烟酸的定量检测

表面增强拉曼光谱技术对分子具有特异性识别以及快速无损检测的能力,使其在药物检测方面具有重大的潜力。通过贵金属和氮化钛之间协同作用,使复合基底具有较高的SERS性能,提供了一种基于SERS技术的药物检测方法。采用电化学沉积及自组装法,制备出贵金属/氮化钛复合薄膜。研究表明,在复合薄膜中存在面心立方晶型TiN、金属单质Au和Ag三种物相;电子显微镜显示平均粒径分别为90和50 nm的金属Au和Ag颗粒均匀分布在TiN薄膜表面;基底的紫外-可见吸收图谱中出现了贵金属金与银纳米颗粒及TiN薄膜三者的特征等离子体共振吸收峰。以该复合薄膜为SERS基底,对烟酸溶液进行拉曼检测。结果显示,贵金属/氮化钛复合薄膜对烟酸具有显著的SERS效应,最低检测浓度为10-5 mol·L-1,对1 033 cm-1处烟酸拉曼信号强度及浓度取对数,发现两者间呈一定线性关系,其R2为0.969,得益于TiN,Au和Ag之间可发生表面等离子体共振引起电磁场增强,以及电荷转移效应。研究还发现,烟酸通过COO-基团垂直吸附在贵金属/氮化钛基底表面;在酸性环境下,烟酸N原子质子化主要以阳离子N＋H（Ⅰ）形式存在;在碱性环境时,主要以阴离子COO-（Ⅲ）形式存在。绞股蓝总甙溶液中模拟烟酸非法添加,该复合基底对其最低的拉曼检测浓度是10-5 mol·L-1,为现场快速检测非法添加药物提供了新途径。     

Enhancements in intensity and thermal stability of Raman spectra based on roughened gold substrates modified by underpotential deposition of silver

In this study, electrochemically roughened gold is modified with underpotential deposition (UPD) silver to investigate the effects on enhancements in the intensity and the thermal stability of surface‐enhanced Raman scattering (SERS). The SERS of Rhodamine 6G (R6G) adsorbed on the UPD Ag‐modified Au substrate exhibits a higher intensity by six‐fold of magnitude, as compared with that of R6G adsorbedon the unmodified Au substrate. Moreover, the SERS enhancement capabilities of UPD Ag‐modified Au and unmodified Au substrates are seriously depressed at temperatures higher than 200 and 150 °C, respectively. It indicates that the modification of UPD Ag can significantly depress the thermal destruction of SERS‐active substrates. Copyright © 2009 John Wiley & Sons, Ltd.     

沉积铁钝化膜的傅立叶变换表面增强拉曼光谱

利用恒电流沉积技术、傅立叶变换表面增强拉曼散射技术现场研究了0 1mol/LNaOH溶液中铁金属电极在不同电位下的表面氧化物的组成。结果表明,在电极预钝化区,表面首先生成的Fe(OH)2可由拉曼谱图中出现的550cm-1表征,证实了以往的研究结果。进入钝化区,表面二价氧化物逐步转化为高价氧化物Fe3O4及α 、δ 和γ FeOOH。在电位回扫的过程中,各氧化产物的还原以及铁表面SERS活性的逐渐消失导致谱峰强度降低。     

The effect of underpotentially deposited Pb on the surface enhanced Raman scattering ability of polycrystalline Ag

The effect of submonolayer and monolayer amounts of Pb deposited at underpotential on a polycrystalline Ag electrode surface on the surface enhanced Raman scattering behavior of pyridine and Cl^? adsorbates is presented. Surfaces covered by greater than 70% of a Pb monolayer do not support significant surface enhancement. The changes observed in SERS intensity as a function of fractional Pb coverage are interpreted in terms of changes in surface electronic properties and changes in adsorbate coverage. Evidence for changes in the structure of the Pb overlayer is also presented. Investigation of the reversibility of the SERS behavior after deposition and quantitative stripping of varying amounts of Pb provides information on the roles played by various sizes of surface roughness in SERS. These data suggest that both large scale and atomic scale roughness contribute to the SERS intensities measured in these systems.     

时间分辨表面增强拉曼光谱研究银电极表面硫脲和ClO_4~-共吸附层的结构

本文应用时间分辨表面增强拉曼光谱（ＴＲＳＥＲＳ）结合电位阶跃和电位扫描的方法，研究了硫脲和ＣｌＯ－４在Ａｇ电极表面的共吸附层结构。结果表明ＳＥＲＳ谱峰强度随电极电位的响应速率与电位阶跃扫描的方向有关，ＴＵ和ＣｌＯ－４在Ａｇ表面的共吸附层在不同的电位下存在两种不同的构型，并且两种构型之间转化的难易程度不同。     

PATP在Ag/TiO_2纳米管基底上的表面增强拉曼散射和光催化过程研究

表面增强拉曼散射(SERS)是一种超灵敏、高选择性的分析方法,越来越受到人们的关注。对巯基苯胺(PATP)由于其易吸附在大多数SERS基底表面,并可以产生极强的SERS信号,因此常被用作SERS的探针分子。二氧化钛(TiO_2)是一种目前常用的光催化剂,但是其催化效率仍有待提高。将贵金属与TiO_2复合是提高其催化效率的有效手段。本文采用电化学阳极氧化法制备了二氧化钛纳米管(TiO_2NTs),并采用光化学还原方法在表面沉积了贵金属银,制备了一种同时具有SERS和催化性能的双功能基底,即银纳米粒子修饰的二氧化钛纳米管(Ag/TiO_2NTs),研究了PATP分子在该基底上的光催化过程,并与在银镜基底上的光催化过程进行了比较。我们发现,Ag/TiO_2NTs基底上的PATP在催化过程中峰强度逐渐减弱,但没有新峰的出现;而在银镜基底上PATP的峰强度随光照时间却几乎没有变化,证明了PATP分子在Ag/TiO_2 NTs上的光催化降解过程。本文还对Ag/TiO_2NTs上PATP的催化过程进行了动力学分析,结果表明PATP在该基底表面的催化反应为一级反应。     

Investigation on surface‐enhanced Raman scattering activity on an ex situ ORC roughened nickel electrode

Roughened nickel electrode surfaces have been demonstrated to exhibit a moderate enhanced Raman scattering effect with an enhancing factor of about 10⁴, which is not suitable in some cases for further inhibition adsorbates study. We reported here a new modified roughening procedure of nickel electrodes, by which a high S/N ratio surface‐enhanced Raman spectroscopy (SERS) of pyridine was obtained. At least two major advantages were found for the modified roughening methods: (1) enhancing factor was improved by a factor of about 10, (2) SERS‐active sites were distributed uniformly on the Ni surfaces. Potential‐dependent SERS spectra of a candidate inhibitor molecule benzotriazole (BTAH) adsorbed onto nickel electrodes were briefly presented for verifying the feasibility of the modified roughening method in this paper. Results showed that BTAH molecules were adsorbed on the nickel electrodes in neutral molecule form at more negative potentials and a polymer‐like film with the composition of [Ni_n(BTA)_p]_m formed on the nickel electrodes with the positive shift of potentials. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface-enhanced Raman spectroscopy based on ordered nanocap arrays

We fabricated the Ag cap array for surface-enhanced Raman scattering (SERS) by Ag deposition onto two dimensional polystyrene colloid sphere templates, and 4-mercaptopyridine (4-MPy) was used as the probing molecule. When the colloids with different size were chosen as the substrate for 20 nm Ag deposition, the film on 100 nm colloids gave the significant enhancement. SERS intensity increased with the increase of Ag thickness. When 20 nm Ag film was coated by Ta, the SERS signals decreased with the increase of Ta thickness, indicating the main effect from the top of cap structure. When Co layer was added under the Ag film, the SERS intensity decreased with the increase of Co thickness because the Co layer affects electromagnetic and plasmon resonance.     

Nanogaps in 2D Ag‐nanocap arrays for surface‐enhanced Raman scattering

The surface‐enhanced Raman scattering substrate of Ag–Ag nanocap arrays are prepared by depositing Ag film onto two‐dimensional (2D) polystyrene colloidal nanosphere templates. When the original colloidal arrays are used as the substrate for Ag deposition, surface‐enhanced Raman scattering (SERS) enhancements show the strong size‐dependence behaviours. When O₂‐plasma etched 2D polystyrene templates are used as the substrate for Ag deposition to form nanogaps, the gap sizes between adjacent Ag nanocaps from 5 to 20 nm generate even greater SERS enhancements. When SiO₂ coverage is deposited to isolate the Ag nanocaps from the neighbours, the SERS signals are enhanced more. The significant SERS effects are due to the coupling between Ag nanocaps controlled by the distance, which enhances the local electric‐field intensity. Copyright © 2013 John Wiley & Sons, Ltd.