Surface Plasmon Enhanced Chemical Reactions on Metal Nanostructures

Noble metal nanomaterials as plasmonic photocatalysts can strongly absorb visible light and generate localized surface plasmon resonance (SPR), which in turn depends on the size, shape, and surrounding of the plasmonic metal nanomaterials (PMNMs). Remarkably, the high-efficiency conversion of solar energy into chemical energy was expected to be achieved by PMNMs. Therefore, researchers have chosen PMNMs to improve the photocatalytic activity toward targeted molecules. This enhancement can be achieved by the effective separation of photogenerated electrons and holes of the PMNMs in the presence of light. Surface-enhanced Raman spectroscopy (SERS) has been performed for obtaining information about the photochemically transformed surface species at molecular levels. A profound understanding of kinetic mechanisms is needed for the development of novel plasmonic catalysts toward various chemical transformations of targeted molecules. In this chapter, based on the above discussions, the participation of SPR excitation in PMNMs and photocatalysis toward chemical transformations of SERS-active organic molecules such as aromatic amino and nitro compounds based on PMNMs have been discussed in detail through theoretical and experimental studies. Eventually, a summary and the future directions of this study are discussed

THEORETICAL STUDY OF SURFACE-ENHANCED RAMAN SPECTRA OF WATER AND IONIC COMPLEXES IN ELECTROCHEMICAL INTERFACES

Water plays a very important role in surface science of electrochemical interfaces, closely associated with energy source, environment, our living, and life processes. However, it is very difficult to be observed from normal Raman spectra of water in electrochemical interfaces. Although the surface-enhanced Raman scattering effect can have million-fold Raman signal enhancement for molecules on adsorbed silver and gold electrodes of nanostructures, the surface-enhanced Raman spectrum of water is hard to be measured due to its very small Raman scattering cross section, weak adsorption ability, and very few surface molecular number relative to the bulk. Thus only electrochemical SERS spectra of water have been observed in electrode/electrolyte interfaces so far. Our present work focuses on the chemical enhancement from hydrogen bonding interaction, surface adsorption, halide ions, interfacial electric field effects on SERS signals of water adsorbed on silver electrodes, by combining the metallic cluster model and hybrid density functional theory (DFT-B3LYP) methods. The interfacial structures, binding interactions and the anion effect from different halides including chloride, bromide, and iodide ions have been analyzed and compared with experimental measurements in literatures. Then the excited states of halide ions modified active sites on roughened silver electrode have been discussed. Especially, our time-dependent DFT (TD-DFT) calculations predicted that halide ions can form low-lying excited states of surface complexes, like the photon-induced electron transfer states, and finally contribute to the chemical enhancement of SERS signals of water. Furthermore, we proposed that the halide effect on the relative SERS intensities of water is a good example for understanding the chemical enhancement of SERS active sites modified by halide ions in electrochemical systems

ELECTROCHEMICAL SURFACE-ENHANCED RAMAN SPECTRA AND PLASMON-DRIVEN PHOTOELECTROCHEMICAL REACTION OF P-AMINOTHIOPHENOL ON SILVER ELECTRODE OF NANOSTRUCTURES

Surface plasmon resonance (SPR) of noble metal nanoparticles (NPs) provides a pathway to efficiently absorb and confine light to nanoscale surface electrons, thereby bridging photonics and photoelectrochemistry. This not only produces the giant Raman intensity enhancement in surface-enhanced Raman spectroscopy (SERS), but also results in plasmon-driven chemical reaction on metal nanostructures. We have studied the surface-enhanced Raman spectra of p-aminothiophenol adsorbed on silver electrodes of nanostructures. In this work, we studied SPR-enhanced photoelectrochemical synergistic reactions by SERS to improve chemical reaction activity and examine changes in reaction selectivity. We first demonstrate that hot carriers arising from SPR decay contribute to the surface catalytic coupling reaction of PATP on a silver NP electrode. Then, by using potential step electrochemical SERS, we further inspect the kinetics of the surface catalytic coupling reaction by monitoring the time-dependent SERS intensity of the characteristic band at 1436 cm$^{-1}$, which can be attributed to the stretching vibration of the N=N double bond of p,p’-dimercaptoazobenzene (DMAB). When synergistically combined with the modulation of pH at electrochemical interfaces, SPR-enhanced photoelectrochemical reactions can be further gain reaction efficiency and selectivity for the formation of DMAB and other surface species at higher potentials. The electrochemical SPR effect provides a viable approach for studying the photoelectrochemistry through combining SERS at the interface of nanoparticle-modified metal electrodes and electrolytes

Theoretical study on surface-enhanced raman spectra of water adsorbed on noble metal cathodes of nanostructures

The observed surface-enhanced Raman scattering (SERS) spectra of water adsorbed on metal film electrodes of silver, gold, and platinum nanoparticles were used to infer interfacial water structures. The basis is the change of the electrochemical vibrational Stark tuning rates and the relative Raman intensity of the stretching and bending modes. How it is not completely understood the reason why the relative Raman intensity ratio of the bending and stretching vibrations of interfacial water increases at the very negative potential region. Density functional theory calculations provide the conceptual model. The specific enhancement effect for the bending mode was closely associated with the water adsorption structure in a hydrogen bonded configuration through its H-end binding to surface sites with large polarizability due to strong cathodic polarization. The present theoretical results allow us to propose that interfacial water molecules exist on these metal cathodes with different hydrogen bonding interactions, the HO-H…Ag(Au) for silver and gold. In acidic solution, a surface electron–hydronium ion-pair was proposed as an adsorption configuration of interfacial water structures on silver and gold cathodes based on density functional theory (DFT) calculations. The EHIP is in the configuration of H$_{3}$O$^{+}$(H$_{2}$O)$_{n}$e$^{-}$, where the hydronium H$_{3}$O$^{+}$ and the surface electron is separated by water layers. The electron bound in the EHIP can first be excited under light irradiation, subsequently inducing a structural relaxation into a hydrated hydrogen atom. Thus, Raman intensities of the interfacial water in the EHIP species are signifcantly enhanced due to the cathodic polarization on silver and gold electrodes

Theoretical study on sers of wagging vibrations of benzyl radical adsorbed on silver electrodes

Electrochemical surface-enhanced Raman spectroscopy (EC-SERS) has been used to characterize adsorbed species widely but reaction intermediates rarely on electrodes. In previous studies, the observed SERS signals were proposed from surface benzyl species due to the electrochemical reduction of benzyl chloride on silver electrode surfaces. In this work, we reinvestigated the vibrational assignments of benzyl chloride and benzyl radical as the reaction intermediate. On the basis of density functional theoretical (DFT) calculations and normal mode analysis, our systematical results provide more reasonable new assignments for both surface species. Further, we investigated adsorption configurations, binding energies, and vibrational frequency shifts of benzyl radical interacting with silver. Our calculated results show that the wagging vibration displays significant vibrational frequency shift, strong coupling with some intramolecular modes in the phenyl ring, and significant changes in intensity of Raman signals. The study also provides absolute Raman intensity in benzyl halides and discuss the enhancement effect mainly due to the binding interaction with respect to free benzyl radical

Modelling the electronic structure and magnetic properties of LiFeAs and FeSe using hybrid-exchange density functional theory

The electronic structure and magnetic properties of LiFeAs and FeSe have been studied using hybrid exchange density functional theory. The total energies for a unit cell in LiFeAs and FeSe with different spin states including non-magnetic and spin-2 are calculated. The spin-2 configuration has the lower energy for both LiFeAs and FeSe. The computed anti-ferromagnetic exchange interactions between spins on the nearest (next nearest) neighbouring Fe atoms in LiFeAs and FeSe are approximately 14 (17) meV and 6 (13) meV respectively. The total energies of the checkerboard and stripe-type anti-ferromagnetic ordering for LiFeAs and FeSe are compared, yielding that for LiFeAs the checkerboard is lower whereas for FeSe the stripe-type is lower. However, owing to the fact that the exchange interaction of the next nearest neighbour is larger than that of the nearest one, which means that the collinear ordering might be the ground state. These results are in agreement with previous theoretical calculations and experiments. Especially the calculations for LiFeAs indicate a co-existence of conducting d-bands at the Fermi surface and d-orbital magnetism far below the Fermi surface. The theoretical results presented here might be useful for the experimentalists working on the electronic structure and magnetism of iron-based superconductors.Comment: 7 pages, 4 figures, 1 table, accepted by Solid State Communication

Qubitization of Bosons

A binary mapping from Fock space of bosonic state to qubits is given. Based on the binary mapping, we construte an algorithm of qubitization of bosons with complexity O(log(N)). As an example, the algorithm of qubitization of bosons in matrix product state to simulate real time dynamics of Yukawa coupling is realized. The calculation error bar is estimated by random sampling method. This proposal may be achieved in superconductivity noisy intermediate--scale quantum computer not far future.Comment: 7 pages, 4 figure

The color gradients of spiral disks in the Sloan Digital Sky Survey

We investigate the radial color gradients of galactic disks using a sample of about 20,000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey (SDSS-DR4). We combine galaxies with similar concentration, size and luminosity to construct composite galaxies, and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies (R_{50}<3 kpc), almost all galaxies show negative disk color gradients with mean g-r gradient G_{gr}=-0.006 mag kpc^{-1} and r-z gradient G_{rz}=-0.018 mag kpc^{-1}. The disk color gradients are independent of the morphological types of galaxies and strongly dependent on the disk surface brightness \mu_{d}, with lower surface brightness galactic disks having steeper color gradients. We quantify the intrinsic correlation between color gradients and surface brightness as G_{gr}=-0.011\mu_{d}+0.233 and G_{rz}=-0.015\mu_{d}+0.324. These quantified correlations provide tight observational constraints on the formation and evolution models of spiral galaxies.Comment: 20 pages, 5 figures, Accepted for publication in RAA (Research in Astronomy and Astrophysics

Association of Intrarenal B-Cell Infiltrates with Clinical Outcome in Lupus Nephritis: A Study of 192 Cases

Background. Lupus nephritis (LN) remains a major cause of morbidity and end-stage renal disease. Dysfunction of B lymphocytes is thought to be important in the pathogenesis of SLE/LN. Intrarenal B cells have been found in several forms of inflammatory kidney diseases although their role in LN renal is not well defined. Methods. Intrarenal B cells were analyzed in 192 renal biopsies from patients diagnosed with lupus nephritis. Immunohistochemical staining of serial sections was performed for each LN patient using CD20, CD3, and CD21 antibodies. Results. Intrarenal B cells were more likely to be associated with class IV LN and were mainly distributed in the renal interstitium, with very few in the glomerulus. The systemic lupus erythematosus disease activity index (SLEDAI), blood urea nitrogen, and serum creatinine levels were all significantly greater in the LN-B cell groups (all P<0.05). LN renal activity and chronicity indices correlated with B-cells infiltrates (all P<0.0001). Renal biopsies were classified into four distinct categories according to the organizational grade of inflammatory cell infiltrates. Germinal center- (GC-) like structures were not identified in any LN biopsies. Conclusion. It is hypothesized that intrarenal B cells enhance immunological responses and exaggerate the local immune response to persisting autoimmune damage in the tubulointerstitium