Light emitted by molecules embedded within metal nanoparticle clusters is strongly enhanced by interaction with surface plasmons. This allows, for example, the observation of Raman scattering from individual molecules. The symmetry of the metal cluster may affect the Raman-scattered light by generating new polarization states. This article reviews the use of symmetry theory to analyze the plasmonic normal modes of metal nanoparticle trimers. The lowest bright energy modes are degenerate for an equilateral triangle but split when the symmetry is broken. When a single molecule in the gap between two of the particles emits, it excites the plasmon modes, typically off-resonance, and the ensuing interference between the modes rotates the polarization of the emitted light. This so-called Raman optical activity can generate circularly polarized light at the Raman frequency. This curious phenomenon, which was demonstrated experimentally, may prove useful for future plasmonic devices.

Discovered by Richard Van Duyne in 1976, surface-enhanced Raman spectroscopy (SERS) has enjoyed a continual expansion in interest over the past 36 years benefitting from a series of discoveries, new fields, and technological capabilities, all of which have greatly contributed to the current broad interest in this topic. The focus on nanoscience and nanotechnology that began in the early 1990s naturally put a spotlight on SERS as a quintessentially nanoscale phenomenon. This article discusses some of the key field-shaping developments in SERS from a historical and a materials perspective, providing background for the articles in this issue of MRS Bulletin.

The atoms at the surfaces of materials represent the frontier separating the bulk from the surrounding medium. Over the last decades, scientists have intensely studied the structure and properties of surfaces with the goal of understanding and improving the electronic and chemical properties of materials. The surface–medium interaction determines wetting, friction, chemical, biological, and electronic properties. The activity of catalysts, phenomena occurring in water droplets and particles in the atmosphere, and the electronic properties of semiconductor devices are direct consequences of surface-environment interactions. While the need to pursue studies in the normal environment that surrounds a material has always been recognized, the techniques used in the past have only partially fulfilled this need, as most of them work best under high vacuum conditions. My research over the last 10 years has focused on discovering the structure of a surface and its dynamics in real life—in everyday environments. This required the development of new techniques and methods. I present some of the new tools developed in my laboratory and new properties that were discovered by their application in the areas of environmental science, surface chemistry, and catalysis.

Surface-enhanced Raman spectroscopy (SERS) is highly dependent upon the substrate, where excitation of the localized metal surface plasmon resonance enhances the vibrational scattering signal of proximate analyte molecules. This article reviews recent progress in the fabrication of SERS substrates and the requirements for characterization of plasmonic materials as SERS platforms. We discuss bottom-up fabrication of SERS substrates and illustrate the advantages of rational control of metallic nanoparticle synthesis and assembly for hot spot creation. We also detail top-down methods, including nanosphere lithography for the preparation of tunable, highly sensitive, and robust substrates, as well as the unique benefits of tip-enhanced Raman spectroscopy for simultaneous acquisition of molecular vibrational information and high spatial resolution imaging. Finally, we discuss future prospects and challenges in SERS, including the development of surface-enhanced femtosecond stimulated Raman spectroscopy, microfluidics with SERS, creating highly reproducible substrates, and the need for reliable characterization of substrates.

This paper examines the onset and progression of dynamic recrystallization (DRX) phenomena under shear deformation conditions characterized by strains >1 and strain rates >102/s by purposing large strain machining (LSM) as a test of microstructure response. To accomplish this, samples are created using LSM while characterizing the deformation using digital image correlation and infrared thermography. Microstructural consequences resulting from the characterized thermomechanical conditions are examined using electron backscattered diffraction. The progression of DRX is measured by identifying the threshold of grain orientation spread demarcating the onset of recrystallization and utilizing this threshold to segregate the microstructure and quantify the extent of DRX. A model for the onset of DRX as a function of thermomechanics of deformation is presented. This characterization can help understand surface microstructures resulting from shear-based manufacturing processes, such as turning, milling, shaping, etc., that are created under analogous thermomechanical conditions.