Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

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Plasmonics: Fundamentals and Applications

SERS: Materials, applications, and the future

Since 2000, there has been an explosion of activity in the field of plasmon-enhanced Raman spectroscopy (PERS), including surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In this Review, we explore the mechanism of PERS and discuss PERS hotspots — nanoscale regions with a strongly enhanced local electromagnetic field — that allow trace-molecule detection, biomolecule analysis and surface characterization of various materials. In particular, we discuss a new generation of hotspots that are generated from hybrid structures combining PERS-active nanostructures and probe materials, which feature a strong local electromagnetic field on the surface of the probe material. Enhancement of surface Raman signals up to five orders of magnitude can be obtained from materials that are weakly SERS active or SERS inactive. We provide a detailed overview of future research directions in the field of PERS, focusing on new PERS-active nanomaterials and nanostructures and the broad application prospect for materials science and technology. Assisted by rationally designed novel plasmonic nanostructures, surface-enhanced Raman spectroscopy has presented a new generation of analytical tools (that is, tip-enhanced Raman spectroscopy and shell-isolated nanoparticle-enhanced Raman spectroscopy) with an extremely high surface sensitivity, spatial resolution and broad application for materials science and technology.

Nanostructure-based plasmon-enhanced Raman spectroscopy for surface analysis of materials

Surface-enhanced Raman spectroscopy (SERS) and related spectroscopies are powered primarily by the concentration of the electromagnetic (EM) fields associated with light in or near appropriately nanostructured electrically-conducting materials, most prominently, but not exclusively high-conductivity metals such as silver and gold. This field concentration takes place on account of the excitation of surface-plasmon (SP) resonances in the nanostructured conductor. Optimizing nanostructures for SERS, therefore, implies optimizing the ability of plasmonic nanostructures to concentrate EM optical fields at locations where molecules of interest reside, and to enhance the radiation efficiency of the oscillating dipoles associated with these molecules and nanostructures. This review summarizes the development of theories over the past four decades pertinent to SERS, especially those contributing to our current understanding of SP-related SERS. Special emphasis is given to the salient strategies and theoretical approaches for optimizing nanostructures with hotspots as efficient EM near-field concentrating and far-field radiating substrates for SERS. A simple model is described in terms of which the upper limit of the SERS enhancement can be estimated. Several experimental strategies that may allow one to approach, or possibly exceed this limit, such as cascading the enhancement of the local and radiated EM field by the multiscale EM coupling of hierarchical structures, and generating hotspots by hybridizing an antenna mode with a plasmonic waveguide cavity mode, which would result in an increased local field enhancement, are discussed. Aiming to significantly broaden the application of SERS to other fields, and especially to material science, we consider hybrid structures of plasmonic nanostructures and other material phases and strategies for producing strong local EM fields at desired locations in such hybrid structures. In this vein, we consider some of the numerical strategies for simulating the optical properties and consequential SERS performance of particle-on-substrate systems that might guide the design of SERS-active systems. Finally, some current theoretical attempts are briefly discussed for unifying EM and non-EM contribution to SERS.

Electromagnetic theories of surface-enhanced Raman spectroscopy

The nature and properties of surface-enhanced vibrational spectra of molecules adsorbed on surfaces that can enhance the absorption and the emission of electromagnetic radiation are discussed. Examples of surface-enhanced resonant Raman scattering, surface-enhanced Raman scattering in the near-infrared and surface-enhanced infrared are given. The rough surfaces used are metal island films coated with a nanometric organic film using the Langmuir-Blodgett technique or deposited by vacuum evaporation.

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Surface enhanced vibrational spectroscopy

We report the first observation of surface-enhanced Raman scattering (SERS) excited with ultraviolet (UV) light from transition metal electrodes. Adsorbed pyridine and SCN- on rough rhodium (Rh) and ruthenium (Ru) electrodes, respectively, have been studied using 325 nm laser excitation. In contrast, the best enhancers in the visible and near infrared, silver and gold, do not produce UV-SERS. The experimental data of UV-SERS are in agreement with our preliminary theoretical calculation based on the electromagnetic enhancement mechanism. The enhancement factor is about 2 orders of magnitude for the Rh and Ru electrodes when they are excited at 325 nm.

Surface-enhanced Raman scattering in the ultraviolet spectral region: UV-SERS on rhodium and ruthenium electrodes

Confocal microprobe Raman spectroscopic study of the electrochemical reduction of benzene on platinum and rhodium electrodes

The electrochemical halogenation of benzene: an in situ confocal microprobe Raman study

The invention discloses a surface-enhanced Raman scattering substrate material, a preparation method and an application thereof. The substrate material is a three-layer composite structure: the lower layer is an Au (at) Ag nanoparticle monofilm; the middle layer is a propanethiol molecular layer modified on the Au (at) Ag film; and the upper layer is a polydimethylsiloxane film of 200-400 nm thick. According to the three-layer composite structural substrate material, the polydimethylsiloxane film enriches mononuclear aromatics gaseous molecules in flowing gas through physical action, propanethiol adsorbs the molecules onto the surface of the Au (at) Ag film to carry out enhanced detection. Thus, toxic atmospheric pollutants can be effectively enriched, fixed and detected. Especially for detection of methylbenzene, benzene and xylene in a flowing gaseous phase, detection signal intensity is enhanced by more than 50 times. The invention provides a more sensitive new method for detection of relevant pollutants in industrial waste gas and in the atmospheric environment.

Surface-enhanced Raman scattering substrate material, preparation method and application thereof

The invention discloses a preparation method for resizable hypercircle gold-silver alloy nanoparticles The preparation method comprises the following step (1) of reducing chloroauric acid by taking sodium citrate and hydroxylamine hydrochloride as reductants step by step to obtain first sols; the step (2) of coating silver on the surfaces of gold nanoparticles in the first sols obtained in the step (1) in sequence to obtain second sols; the step (3) of coating gold on the surfaces of the nanoparticles of Au@Ag core shell structure in the second sols obtained in the step (2) to obtain third sols; and the step (4) of conducting ultrafast laser melting on the core shell structure nanoparticles of Au@Ag@Au structure in the third sols obtained in the step (3) to synthesize the hypercircle gold-silver alloy nanoparticles The hypercircle gold-silver alloy nanoparticles prepared with the preparation method disclosed by the invention are regular in shape which is nearly perfect sphere, and are composed of gold inner cores and gold-silver alloy shells; and the gold-silver alloy structure of the shells has the performance which is different from the performance of one-component gold or silver

Guo-kun Liu

Papers

Surface-enhanced Raman scattering in the ultraviolet spectral region: UV-SERS on rhodium and ruthenium electrodes

Confocal microprobe Raman spectroscopic study of the electrochemical reduction of benzene on platinum and rhodium electrodes

The electrochemical halogenation of benzene: an in situ confocal microprobe Raman study

Surface-enhanced Raman scattering substrate material, preparation method and application thereof

Preparation method for resizable hypercircle gold-silver alloy nanoparticles