Orientation dependence of surface enhanced raman intensities: results from abinitio calculations

Time dependent Hartree—Fock methods have been used to calculate Raman intensifies for H₂ adsorbed onto a model lithium cluster as a function of the orientation of H₂ relative to the cluster surface. The intensity is found to be largest for perpendicular adsorption, dropping to a small value at an intermediate angle, and then rising to a second but smaller maximum for parallel adsorption. The results are interpreted using a model which correlates enhancement to lithium cluster orbital energy shifts induced by the static quadrupole field Of H₂.     

Strongly enhanced orbital moments and anisotropies of adatoms on the Ag(001) surface

We present ab initio calculations for orbital moments and anisotropy energies of 3d and 5d adatoms on the Ag(001) surface, based on density functional theory, including Brooks' orbital polarization (OP) term, and applying a fully relativistic Korringa-Kohn-Rostoker-Green's function method. In general, we find unusually large orbital moments and anisotropy energies, e.g., in the 3d series, 2.57 mu(B) and +74 meV for Co, and, in the 5d series, 1.78 mu(B) and +42 meV for Os. These magnetic properties are determined mainly by the OP and even exist without spin-orbit coupling.     

Evaluation of critical exponents from raman intensities

Theory and experiment are compared for Raman intensities near continuous structural phase transitions. Situations in which the order parameter couples linearly to light or quadratically are considered. Both cases are easily analyzed for the soft modes in ferroelastic LnP₅O₁₄ (Ln = La, Pr, Nd, Tb). The trace polarizability tensor yields β = 0.49 ± 0.02; off-diagonal terms give γ’ = 1.16 ± 0.15 and γ = 1.07 ± 0.10. Mean field results are also obtained for barium sodium niobate near T (incommensurate) = 582 K and for tris-sarcosine calcium chloride near T _c = 128 K.     

Time dependence of surface enhanced raman scattering during and after oxidation-reduction cycles

The time-development of surface enhanced Raman scattering from silver electrodes immersed in simple electrolytes has been measured during and after oxidation-reduction cycles of the linear scan double step type. Raman spectra were recorded in times as short as 0.1 second, using a spectrograph equipped with an optical multichannel detector and analyzer. Correlations between Raman spectra and current or charge passed were found, and in mixed electrolytes the displacement of one anion by a more strongly adsorbing anion was observed. In addition, unexpectedly strong effects of laser irradiation and hydrogen evolution prior to the oxidation-reduction cycle have been observed in the intensity of SERS bands after the cycle. These last two effects are attributed to peculiar surface morphologies.     

Determination of the coverage of an Au overlayer on an Ag island film using surface enhanced raman scattering

The coverage of an Au overlayer on an Ag island film has been measured using surface enhanced Raman scattering from chemisorbed SO⁻₃. XPS was also employed to determine the chemisorption.     

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.     

Self-organization of Cs adatoms on Ag(111) caused by quantum confinement of surface electrons on Ag clusters

The effect of quantum confinement formed by Ag nanoclusters on the self-organization of Cs adatoms on Ag(111) was studied. The existence of allowed and forbidden zones was found for the diffusion motion of Cs adatoms near and on top of the clusters. The formation of the orbits of an adatom’s motion was demonstrated for self-organization process in a Cs adatom ensemble near and on top of the clusters.     

Effect of satellite Q-branches on temperatures computed from oxygen vibrational raman intensities

Splitting of the ³Σ^-_g ground state of molecular oxygen has a small but noticeable effect on the intensity distribution in the fundamental and hotband Raman Q-branches. An analysis of oxygen Q-branch spectra [computed for Hund's coupling case (b) and pure anisotropic scattering], with expressions corresponding to ¹Σ theory, results in temperature errors of -2.0% to -0.5% in the range 500–2000 K.     

银纳米线表面等离激元波导的能量损耗

金属纳米结构的表面等离激元可以突破光学衍射极限,为光子器件的微型化和集成光学芯片的实现奠定基础.基于表面等离激元的各种基本光学元件已经研制出来.然而,由于金属结构的固有欧姆损耗以及向衬底的辐射损耗等,表面等离激元的传输能量损耗较大,极大地制约了其在纳米光子器件和回路中的应用.研究能量损耗的影响因素以及如何有效降低能量损耗对未来光子器件的实际应用具有重要意义.本文从纳米线表面等离激元的基本模式出发,介绍了它在不同条件下的场分布和传输特性,在此基础上着重讨论纳米线表面等离激元传输损耗的影响因素和测量方法以及目前常用的降低传输损耗的思路.最后给出总结以及如何进一步降低能量损耗方法的展望.表面等离激元能量损耗的相关研究对于纳米光子器件的设计和集成光子回路的构建有着重要作用.     

Diffusivity of adatoms on plasma-exposed surfaces determined from the ionization energy approximation and ionic polarizability

Microscopic surface diffusivity theory based on atomic ionization energy concept is developed to explain the variations of the atomic and displacement polarizations with respect to the surface diffusion activation energy of adatoms in the process of self-assembly of quantum dots on plasma-exposed surfaces. These polarizations are derived classically, while the atomic polarization is quantized to obtain the microscopic atomic polarizability. The surface diffusivity equation is derived as a function of the ionization energy. The results of this work can be used to fine-tune the delivery rates of different adatoms onto nanostructure growth surfaces and optimize the low-temperature plasma based nanoscale synthesis processes.     

The influence of temperature on surface enhanced Raman scattering in the electrochemical environment: Evidence for adatoms

The surface enhanced Raman signal from the Cl-surface stretch vibration on Ag in aqueous KCl is irreversibly quenched by thermal dissociation of Ag-adatom-Cl-surface complexes. In a KF electrolyte, where a low concentration of Ag⁺ ions is present, temperature changes alter the steady state adatom concentration and give rise to reversible changes in the inelastic continuum background Raman signal.     

Influence of isolated adatoms on surface electronic states

The electron spectrum of a crystal with an adsorbed centre is considered, using the mathematical techniques of the quantum mechanical theory of scattering. A special pole approximation is developed which is substantiated by specific features of the problem. Formulas are derived for the adsorption-caused changes of the thermodynamical characteristics and compared with the experimental data. The behaviour of the density of states as an adatom recedes away from the crystal is elucidated. The dynamic effects of surface states are considered using field emission as an example. The formula obtained is compared with experiment.     

Preparation of gold electrodes for surface enhanced Raman spectroscopy SERS

An electrochemical method for preparation of electrodes for SERS involving repetitive dissolution-deposition potential cycling of a polycrystalline, smooth gold electrode is described, which can be applied in both halide-free and halide containing solutions. The SERS-active electrodes obtained this way can be cleaned effectively and subsequently exposed to electrolyte solutions containing adsorbable molecules. No trapping of molecules or ions present during the activation is found in SER spectra, the signal-to-noise ratio obtained with these electrodes even allows detection of weakly adsorbed species.     

纳米Ag材料表面等离子体激元引起的表面增强拉曼散射光谱研究

用热蒸发的方法制备了纳米Ag材料,并用扫描电子显微镜对纳米粒子进行了形貌的表征,通过紫外—可见分光光度计得到Ag纳米粒子的透过谱,得到了Ag纳米粒子的表面等离子体共振的峰值位置.以罗丹明6G为探针分子测定Ag纳米粒子衬底的表面增强拉曼散射效应,通过拉曼散射光谱与透过谱研究了由表面等离子体激元的强极化场引起的表面增强拉曼散射效应,结合透过谱与拉曼增益因子提出了一种描述表面等离子体光学和电学特性的方法,并结合扫描电镜的结果给出了不同结构的纳米Ag材料对表面等离子体激元强度的影响. 关键词： 热蒸发 纳米Ag材料 表面等离子体 表面增强拉曼散射     

Influence of applied potential on bradykinin adsorption onto Ag,Au, and Cu electrodes

Surface‐enhanced Raman scattering, electrochemistry, and generalized two‐dimensional correlation analysis (G2DCA) methods were used to characterize bradykinin (BK), a hormone which is known to be involved in small‐cell and non‐small‐cell lung carcinoma and prostate cancer. BK was deposited onto Ag, Au, and Cu electrode surfaces under different applied electrode potentials (−1.000 V to 0.200 V) in aqueous solutions. Based on the analysis of the enhancement, the broadening, and the shifts in the wavenumbers of individual bands, specific conclusions were drawn regarding the peptide geometry and changes in this geometry that occurred when the electrode type and applied electrode potential were varied. Briefly, BK deposited onto the Ag, Au, and Cu electrode surfaces showed bands that were due to the vibrations of moieties in contact with or in close proximity to the electrode surfaces and were thus located on the same side of the polypeptide backbone. These moieties included the Phe, Arg, and Pro residues. The findings for adsorbed BK were fully supported by G2DCA, which also allowed us to determine the order in which changes occurred when the electrode potential was changed. In addition, it was found that at negative electrode potentials, the Phe rings and methylene groups interact with Ag electrode surface. No such interaction was observed for Au and Cu electrodes. Copyright © 2013 John Wiley & Sons, Ltd.     

Non-monotonous dependence of surface roughness on factors influencing energy of adatoms during thin island film growth

Many experimental results show that surface roughness of thin films can increase, decrease, stay constant or pass through the minimum with the change in substrate temperature, energy of arriving atoms or assisted beam (electrons, photons, ions), depending on material and interval of variation of those parameters. The aim of this paper is to explain and analyze this non-monotonous behavior of surface roughness by proposed kinetic model. The model is based on rate equations and includes processes of surface diffusion of adatoms, nucleation, growth and coalescence of islands in the case of thin films growth in Volmer-Weber mode. It is shown by modeling that non-monotonous dependence of surface roughness on the factors influencing energy of adatoms (e.g. temperature, assisted beam irradiation, accelerating voltage) occurs as a result of interplay between diffusion length of adatoms and size of islands, because both parameters depend on energy of adatoms. Variation of island size and diffusion length results in atomic jumps from islands forming rougher or smoother surface. The functions of surface roughness, island size, island density on diffusion length of adatoms and on other parameters are calculated and analyzed in this work.     

Deposition of Ag nanoparticles on porous anodic alumina for surface enhanced Raman scattering substrate

Ag nanoparticles were exclusively deposited inside the pores of the porous anodic alumina (PAA) template through the deposition cycle including the incubation and the subsequent reduction of Ag(NH₃) . Both the density and size of the produced Ag nanoparticles increased as the deposition cycle number increased. A field‐emission scanning electron microscopeand an ultraviolet‐visible spectrometer were applied, respectively, to study the morphology and the extinction spectra of the Ag nanoparticles. The optimum deposition number was found from the scanning electron microscope (SEM) analysis. Surface enhanced Raman scattering (SERS) spectra of p‐aminothiophenol recorded on the Ag–PAA substrates prepared under increasing number of deposition cycles, manifested an enlarging trend of peak intensity. A point‐by‐point SERS mapping of p‐aminothiophenol on the Ag–PAA substrate was acquired to characterise the homogeneity of the substrate. Copyright © 2008 John Wiley & Sons, Ltd.     

石英拉曼峰进行压力标定的误差研究

在常温常压下进行了作为压标的石英颗粒的拉曼光谱测量和研究。研究结果发现,在25℃和常压条件下,不同的石英颗粒测得的Si—O振动模在463.59～464.65cm-1范围内变化,误差为(±0.1～±0.3)cm-1。其中不同石英颗粒拉曼峰的最大差异达1.06cm-1,远远大于其测量误差。我们认为这是由于石英破碎时使石英颗粒内产生的应力所致。因此,在进行金刚石压腔高温高压实验的压力确定时,必须以常压下实测的Si—O振动模测量值为零压参考点。另外,拉曼光谱仪的波数漂移以及环境温度的不稳定均会造成不可忽视的压力测量误差,应对此进行校正。     

Surface raman electromagnetic enhancement factors for molecules at the surface of small isolated metal spheres: The determination of adsorbate orientation from sers relative intensities

Expressions are derived for the surface Raman electromagnetic enhancement factors and depolarization ratios for a molecule with a general polarizability tensor adsorbed at the surface of a small sphere in the dipole approximation. The constraint of some of the elements of the Raman tensor to zero for molecules with certain elements of symmetry leads to differences in the relative enhancements of modes belonging to different symmetry classes. The least enhanced modes are those whose Raman tensor components involve the two axes in the plane of the surface. The application of these results in a qualitative way to determine the orientation of pyridine at a silver electrode surface is explored, and it is concluded that the pyridine is adsorbed face-on to the electrode surface.