The use of polarization-dependent SERS from scratched gold films to selectively eliminate solution-phase interference

Abstract Polarization-dependent surface-enhanced Raman scattering (SERS) was studied for oxazine 720 molecules adsorbed on a scratched gold surface placed in situ and under electrochemical control. A quantitative method for evaluating the observed polarization dependence will be introduced. This method takes into account the polarization artifacts caused by optical elements in the light microscope used for Raman microscopy. Intensity of the SERS obtained from oxazine 720 adsorbed on scratches in gold showed a polarization dependence after correction was made for these artifacts. In contrast, intensity of the ordinary Raman signal obtained from perchlorate ions in the solution above a scratched gold surface was found to be polarization-independent. Therefore, polarization effects can be used to selectively remove solution-phase interference signals from the SERS spectrum of an adsorbed analyte. These polarization effects were found to be independent of the applied potential, meaning the methodology is applicable to electrochemical SERS studies

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We propose that aromatic nitro and amine compounds undergo photochemical reductive and oxidative coupling, respectively, to specifically produce azobenzene derivatives which exhibit characteristic Raman signals related to the azo group. A photoinduced charge transfer model is presented to explain the transformations observed in para-substituted ArNO 2 and ArNH 2 on nanostructured silver due to the surface plasmon resonance effect. Theoretical calculations show that the initial reaction takes place through excitation of an electron from the filled level of silver to the lowest unoccupied molecular orbital (LUMO) of an adsorbed ArNO 2 molecule, and from the highest occupied molecular orbital (HOMO) of an adsorbed ArNH 2 molecule to the unoccupied level of silver, during irradiation with visible light. The para-substituted ArNO 2 À and ArNH 2 + surface species react further to produce the azobenzene derivatives. Our results may provide a new strategy for the syntheses of aromatic azo dyes from aromatic nitro and amine compounds based on the use of nanostructured silver as a catalyst

Tailoring Au-core Pd-shell Pt-cluster nanoparticles for enhanced electrocatalytic activity

We have rationally synthesized and optimized catalytic nanoparticles consisting of a gold core, covered by a palladium shell, onto which platinum clusters are deposited (Au@Pd@Pt NPs). The amount of Pt and Pd used is extremely small, yet they show unusually high activity for electrooxidation of formic acid. The optimized structure has only 2 atomic layers of Pd and a half-monolayer equivalent of Pt (theta(Pt) approximate to 0.5) but a further increase in the loading of Pd or Pt will actually reduce catalytic activity, inferring that a synergistic effect exists between the three different nanostructure components (sphere, shell and islands). A combined electrochemical, surface-enhanced Raman scattering (SERS) and density functional theory (DFT) study of formic acid and CO oxidation reveals that our core-shell-cluster trimetallic nanostructure has some unique electronic and morphological properties, and that it could be the first in a new family of nanocatalysts possessing unusually high chemical reactivity. Our results are immediately applicable to the design of catalysts for direct formic acid fuel cells (DFAFCs).NSFC[20620130427]; MOST[2007DFC40440]; 973 Program[2009CB930703, 2007CB815303]; ENS; CNRS (UMR, LIA XiamENS)[8640

Revealing the molecular structure of single-molecule junctions in different conductance states by fishing-mode tip-enhanced Raman spectroscopy

The conductance of single-molecule junctions may be governed by the structure of the molecule in the gap or by the way it bonds with the leads, and the information contained in a Raman spectrum is ideal for examining both. Here we demonstrate that molecule-to-surface bonding may be characterized during electron transport by 'fishing-mode' tip-enhanced Raman spectroscopy (FM-TERS). This technique allows mutually verifiable single-molecule conductance and Raman signals with single-molecule contributions to be acquired simultaneously at room temperature. Density functional theory calculations reveal that the most significant spectral change seen for a gold-4,4′-bipyridine-gold junction results from the deformation of the pyridine ring in contact with the drain electrode at high voltage, and these calculations suggest that a stronger bonding interaction between the molecule and the drain may account for the nonlinear dependence of conductance on bias voltage. FM-TERS will lead to a better understanding of electron-transport processes in molecular junctions

Core-shell nanoparticle based SERS from hydrogen adsorbed on a rhodium(111) electrode

We present the first in situ surface Raman spectra of hydrogen on rhodium under electrochemical conditions using gold-core rhodium-shell (Au@Rh) nanoparticles for SERS or gold-core silica-shell (Au@SiO(2)) nanoparticles for SHINERS. The advantage of SHINERS lies in the versatility to study single crystal surfaces such as the H-Rh(111) system.NSF of China[20703032, 11074210, 20620130427, 20533040

In situ dynamic tracking of heterogeneous nanocatalytic processes by shell-isolated nanoparticle-enhanced Raman spectroscopy

原位监测纳米催化反应过程对深入认识反应机理、设计高效催化剂具有重要意义。作为一种具有超高灵敏度的表面分析技术，表面增强拉曼光谱（SERS）是可提供反应过程中催化剂表面吸附物种的丰富信息。然而，仅有Au、Ag、Cu等少数金属在形成特定纳米结构时才能提供较强的拉曼增强，且它们会对催化剂的性质及反应过程产生严重干扰。这就极大地限制了SERS在实际多相催化体系中的应用。鉴于此，该论文发展了一种利用壳层隔绝纳米粒子增强拉曼光谱原位监测纳米催化过程的方法。通过将纳米催化剂组装于壳层隔绝纳米粒子表面，形成SHIENRS卫星结构，利用内核Au纳米粒子增强催化剂表面的拉曼信号，SiO2壳层隔绝Au对催化剂及反应的影响，从而直接获得了纳米催化剂表面物种的真实信息。利用这种SHINERS卫星策略，他们实现了CO氧化反应的原位监测，直接观测到了反应条件下催化剂表面吸附物种。并结合DFT计算，对反应机理进行了阐述。该研究表明SHINERS卫星策略可作为原位跟踪催化反应过程的有效方法，为纳米催化的原位研究提供了一种新的思路。 同时，我校也将在今年12月5-9日举办表面增强拉曼光谱国际会议(International Conference on SERS)，讨论SERS领域的最新进展。会议期间，SERS领域的先驱与权威Richard P. Van Duyne、Martin Moskovits、Andreas Otto以及相关学科的顶级学者Peter G. Bruce、Stefan A. Maier等将作大会报告（会议官方网站http://sers2017.xmu.edu.cn/）。【Abstract】Surface molecular information acquired in situ from a catalytic process can greatly promote the rational design of highly efficient catalysts by revealing structure-activity relationships and reaction mechanisms. Raman spectroscopy can provide this rich structural information, but normal Raman is not sensitive enough to detect trace active species adsorbed on the surface of catalysts. Here we develop a general method for in situ monitoring of heterogeneous catalytic processes through shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) satellite nanocomposites (Au-core silica-shell nanocatalyst-satellite structures), which are stable and have extremely high surface Raman sensitivity. By combining operando SHINERS with density functional theory calculations, we identify the working mechanisms for CO oxidation over PtFe and Pd nanocatalysts, which are typical low- and high-temperature catalysts, respectively. Active species, such as surface oxides, superoxide/peroxide species and Pd–C/Pt–C bonds are directly observed during the reactions. We demonstrate that in situ SHINERS can provide a deep understanding of the fundamental concepts of catalysis.This work was supported by the NSFC (21522508, 21427813, 21373167, 21521004, 21573178 and 21673187), Natural Science Foundation of Guangdong Province (2016A030308012), the Fundamental Research Funds for the Central Universities (20720150039 and 20720160046), ‘111’Project (B16029), and the Thousand Youth Talents Plan of China。 研究工作得到国家自然科学基金优秀青年基金、谱学分析创新研究群体和青年千人计划等资助

Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy: Expanding the Versatility of Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is a powerful technique for detection and characterization because of its extremely high sensitivity and the rich structural information that it can offer. However, most SERS substrates are composed of Au, Ag, or Cu, and a lack of substrate generality has greatly limited the breadth of the use of SERS. Recently, we have devised a method by which SERS can be obtained from virtually any surface. Au nanoparticles are coated with ultrathin silica shells. The Au core provides Raman signal enhancement; the silica shell prevents the core from coming into direct contact with probe/analyte molecules or the surface over which these particles are spread (i.e., prevents the contamination of the chemical system under study). In the present review, we expand upon previous discussion of the enhancement mechanism; procedures for the synthesis and characterization of our nanoparticles; and applications in surface chemistry, electrochemistry, and inspection

A SERS study of thiocyanate adsorption on Au-core Pd-shell nanoparticle film electrodes

NSFC [20620130427]; MOST [2007DFC 40440]; MOST [2007DFC 40440; National Basic Research Program of China [2009CB930703, 2007CB815303]We have systematically studied the adsorption of thiocyanate (SCN-) on gold-core palladium-shell nano-particles (Au@Pd NPs) with different Pd shell thicknesses by surface-enhanced Raman scattering (SERS). When the Pd shell thickness is increased from one to ten atomic layers, the v(C-N) stretching frequency increases 6 cm(-1) for S-bound SCN- and 10 cm(-1) for N-bound SCN-. It infers that the v(C-N) stretching frequency is quite sensitive to electronic properties of the NP surface, but even more so when bonding to Pd occurs through the N atom (at negative potentials) than when it occurs through the S atom (at positive potentials). Data for a second probe, p-aminothiophenol (PATP), was compared to that of SCN-; however, PATP was found to be less sensitive than SCN- to the surface electronic properties of Au@Pd NPs. (C) 2011 Elsevier B.V. All rights reserved

Extraordinary Enhancement of Raman Scattering from Pyridine on Single Crystal Au and Pt Electrodes by Shell-Isolated Au Nanoparticles

NSF of China [21021002, 21033007, 11074210]; MOST of China [2009CB930703]; Swiss National Science Foundation SNF [200021-124643, NRP 62]; Swiss National Science Foundation SNF under CEST; NCF of NWOWe used shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to systematically study the adsorption of pyridine on low-index Au(hkl) and Pt(hkl) single crystal electrodes. Our gold-core silica-shell nanoparticles (Au@SiO(2)NPs) boost the intensity of Raman scattering from molecules adsorbed on atomically flat surfaces. The average enhancement factor reaches 10(6) for Au(110) and 10(5) for Pt(110), which is comparable to or even greater than that obtained for bare gold NPs (a widely adopted SERS substrate). 3D-FDTD simulations reveal that this large enhancement is due to the transfer of the "hotspots" from NP-NP gaps to NP-surface gaps. We also found that the SHINERS intensity strongly depends on the surface crystallographic orientation, with differences up to a factor of 30. Periodic DFT calculations and theoretical analysis of dielectric functions indicate that this facet-dependence is predominantly governed by the dielectric property of the surface. The results presented in this work may open up new approaches for the characterization of adsorbates and reaction pathways on a wide range of smooth surfaces