The optical properties of metal nanoparticles have long been of interest in physical chemistry, starting with Faraday's investigations of colloidal gold in the middle 1800s. More recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range of sizes, shapes, and dielectric environments. In this feature article, we describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment. Included is a description of the qualitative features of dipole and quadrupole plasmon resonances for spherical particles; a discussion of analytical and numerical methods for calculating extinction and scattering cross-sections, local fields, and other optical properties for nonspherical particles; and a survey of applications to problems of recent interest involving triangula...

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The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment

On the basis of different types of experiments, the authors develop implicitly the model of surface-enhanced Raman scattering (SERS) of adsorbates on metal surfaces. The long-range enhancement by resonances of the macroscopic laser and Stokes field is separated quantitatively from the metal electron-mediated resonance Raman effect. The latter mechanism proceeds by increased electron-photon coupling at an atomically rough surface and by temporary charge transfer to orbitals of the adsorbates. This model can account for the chemical specificity and vibrational selectivity of SERS and (partly) for the SERS specificity of the various metals.

https://iopscience.iop.org/article/10.1088/0953-8984/4/5/001/pdf

Surface-enhanced Raman scattering

In the mid-1970s, surface-enhanced Raman scattering (SERS) was discovered which impacted on surface science and spectroscopy because of its extremely high surface sensitivity. However, SERS had not developed as many people had hoped to be a powerful surface diagnostic technique that can be widely used because of some obstacles. For example, only three noble metals Au, Ag, and Cu could provide large enhancement, severely limiting the widespread applications involving other metallic materials of both fundamental and practical importance. In this article, emphasis is put on the recent work of our group to directly generate SERS on net transition metals (e.g., Pt, Ru, Rh, Pd, Fe, Co, Ni, and their alloys) by developing various roughening procedures and optimizing the performance of the confocal Raman microscope. An approach of replacing the randomly roughened surface with ordered nanorod arrays of transition metals is introduced as a promising class of highly SERS-active substrates. The surface enhancement fa...

Surface-Enhanced Raman Scattering: From Noble to Transition Metals and from Rough Surfaces to Ordered Nanostructures

The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH(2)), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates.

https://science.sciencemag.org/content/sci/267/5204/1629.full.pdf

Self-Assembled Metal Colloid Monolayers: An Approach to SERS Substrates.

This article provides an overview of the development and application of the surface-enhanced Raman scattering (SERS) techniques using metal-coated nanostructures on solid substrates An introduction to theoretical principles of the SERS effect and the different SERS-active media is presented The focus is on nanostructured solid substrates and their practical applications in chemical, environmental and biomedical areas Specific examples of analytical techniques, instruments and sensors developed in the author's laboratory will be discussed to illustrate the usefulness and potential of the SERS techniques

Surface-enhanced Raman spectroscopy using metallic nanostructures

The intensity and excitation wavelength dependence of the surface-enhanced Raman effect is measured on microlithographically prepared gold and aluminum particle surfaces. Comparison of enhancement relative to identically fabricated silver surfaces gives good agreement with particle-plasmon theories of surface-enhanced Raman scattering.

Surface-enhanced Raman scattering on gold and aluminum particle arrays

Enhanced optical absorption has been obtained in thin (∼30 nm) layers of hydrogenated amorphous silicon by depositing films on periodically structured substrates. At the appropriate angle of incidence, light is coupled to a surface wave in the abosrbing ‘‘artificial dielectric’’ region formed by the structured interface. This effect is used as the basis of high‐speed metal a‐Si:H metal detectors to overcome the conflicting requirements of high optical absorption and short transit times in thin layers. Peak response as high as 0.16 V is achieved for 50‐pJ incident pulses of picosecond duration. This is comparable to that obtained with much higher mobility crystalline semi‐insulators.

M. B. Stern

Papers

Surface-enhanced Raman scattering on gold and aluminum particle arrays

Periodically structured amorphous silicon detectors with improved picosecond responsivity