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

Graphene is a monolayer of carbon atoms packed into a two-dimensional (2D) honeycomb crystal structure, which is a special material with many excellent properties. In the present study, we will discuss the possibility that graphene can be used as a substrate for enhancing Raman signals of adsorbed molecules. Here, phthalocyanine (Pc), rhodamine 6G (R6G), protoporphyin IX (PPP), and crystal violet (CV), which are popular molecules widely used as a Raman probe, are deposited equally on graphene and a SiO2/Si substrate using vacuum evaporation or solution soaking. By comparing the Raman signals of molecules on monolayer graphene and on a SiO2/Si substrate, we observed that the intensities of the Raman signals on monolayer graphene are much stronger than on a SiO2/Si substrate, indicating a clear Raman enhancement effect on the surface of monolayer graphene. For solution soaking, the Raman signals of the molecules are visible even though the concentration is low to 10(-8) mol/L or less. What's more interesting, the enhanced efficiencies are quite different on monolayer, few-layer, multilayer graphene, graphite, and highly ordered pyrolytic graphite (HOPG). The Raman signals of molecules on multilayer graphene are even weaker than on a SiO2/Si substrate, and the signals are even invisible on graphite and HOPG. Taking the Raman signals on the SiO2/Si substrate as a reference, Raman enhancement factors on the surface of monolayer graphene can be obtained using Raman intensity ratios. The Raman enhancement factors are quite different for different peaks, changing from 2 to 17. Furthermore, we found that the Raman enhancement factors can be distinguished through three classes that correspond to the symmetry of vibrations of the molecule. We attribute this enhancement to the charge transfer between graphene and the molecules, which result in a chemical enhancement. This is a new phenomenon for graphene that will expand the application of graphene to microanalysis and is good for studying the basic properties of both graphene and SERS.

Can graphene be used as a substrate for Raman enhancement

This overview addresses the atomistic aspects of degradation of layered LiMO2 (M = Ni, Co, Mn) oxide Li-ion battery cathode materials, aiming to shed light on the fundamental degradation mechanisms especially inside active cathode materials and at their interfaces. It includes recent results obtained by novel in situ/in operando diffraction methods, modelling, and quasi in situ surface science analysis. Degradation of the active cathode material occurs upon overcharge, resulting from a positive potential shift of the anode. Oxygen loss and eventual phase transformation resulting in dead regions are ascribed to changes in electronic structure and defect formation. The anode potential shift results from loss of free lithium due to side reactions occurring at electrode/electrolyte interfaces. Such side reactions are caused by electron transfer, and depend on the electron energy level alignment at the interface. Side reactions at electrode/electrolyte interfaces and capacity fade may be overcome by the use of suitable solid-state electrolytes and Li-containing anodes.

Fundamental degradation mechanisms of layered oxide Li-ion battery cathode materials: Methodology, insights and novel approaches

Raman microscopy in archaeological science

Resonance Raman spectra are obtained when the wave number of the exciting radiation is close to, or coincident with, that of an electronic transition of the scattering species. Such spectra are usually characterized by a very large enhancement of the intensities of particular Raman bands, sometimes with the appearance of intense overtone and combination tone progressions. The technique provides detailed information about excited electronic states because it is only the vibrational modes associated with the chromophore that are resonance-Raman active. Additionally, the high sensitivity is such that compounds at concentrations as low as 10−6 mol/L may be detected, enabling resonance Raman spectroscopy to be used as an analytical tool and for the study of chromophores in molecules of biological interest.

Resonance Raman Spectroscopy, and Its Application to Inorganic Chemistry. New Analytical Methods (27)

Resonanz-Raman-Spektren werden erhalten, wenn die Wellenzahl der (monochromatischen) Anregungsstrahlung annahernd oder vollstanding mit der eines Elektronenubergangs der streuenden Spezies ubereinstimmt. Normalerweise sind derartige Spektren durch eine sehr grose Intensitatszunahme bestimmter Raman-Banden charakterisiert; manchmal treten auch noch intensive Ober- und Kombinationsschwingungsbanden auf. Die Methode liefert detaillierte Informationen uber angeregte Elektronenzustande, da nur die zu den Chromophoren gehorenden Schwingungszustande Resonanz-Raman-aktiv sind. Hinzu kommt die hohe Empfindlichkeit dieser Technik, die es ermoglicht, Verbindungen sogar noch in Konzentrationen von 10−6 mol/L nachzuweisen. Die Resonanz-Raman-Spektroskopie eignet sich deshalb vor allem auch zum Studium von Chromophoren in biochemisch wichtigen Molekulen.

Resonanz-Raman-Spektroskopie und ihre Anwendung in der Anorganischen Chemie

A theory of A-term resonance Raman scattering is developed for molecular species with several totally symmetric normal coordinates, the potential minimum in the resonant excited state being shifted only slightly from that in the ground state along any one of these coordinates. The theory is then extended to situations in which more than one excited state contributes to the transition polarizability. Equations are developed by which excitation profiles of totally symmetric fundamentals can be calculated. They are then applied to the mixed-valence complexes ruthenium red and ruthenium brown, and their 1,2-diaminoethane analogues. Relative values for the a 1g displacement parameters are calculated in each case for the situation of resonance with the intense, mixed-valence band of each complex at around 20 000 cm-1.

The calculation of A-term resonance Raman excitation profiles

Interference between A- and B-term resonance Raman scattering for totally symmetric modes

The resonance Raman spectra of [Et4N] [FeCl4] in nitromethane solution and of [Bu4N] [FeBr4] as a KBr disc at ≈ 80 K have been record

Trevor J. Dines

Papers

Resonance Raman Spectroscopy, and Its Application to Inorganic Chemistry. New Analytical Methods (27)

Resonanz-Raman-Spektroskopie und ihre Anwendung in der Anorganischen Chemie

The calculation of A-term resonance Raman excitation profiles

Interference between A- and B-term resonance Raman scattering for totally symmetric modes

Resonance Raman studies on [FeCl4]− and [FeBr4]−