Raman scattering electronics applications

See also ATR and Reflectance IR Spectroscopy, Applications High Resolution Electron Energy Loss Spectroscopy, Applications Inelastic Neutron Scattering, Applications Inelastic Neutron Scattering, Instrumentation IR Spectroscopy, Theory Raman and IR Microspectroscopy Surface-Enhanced Raman Scattering (SERS), Applications. 

Nanosize particles (e.g., metals, semiconductors, etc.) are of continuing interest because they possess fascinating catalytic, electronic, and optical properties. Larger particles decorated with smaller nanoparticles on their surface are of interest because of their potential use as heterogeneous catalysts and their relevance in electronic and optical sensor applications as well as surface-enhanced Raman scattering [39,72-75]. 

A large number of possible applications of arrays of nanoparticles on solid surfaces is reviewed in Refs. [23,24]. They include, for example, development of new (elect-ro)catalytical systems for applications as chemical sensors, biosensors or (bio)fuel cells, preparation of optical biosensors exploiting localized plasmonic effect or surface enhanced Raman scattering, development of single electron devices and electroluminescent structures and many other applications. 

Raman spectroscopy is primarily useful as a diagnostic, inasmuch as the vibrational Raman spectrum is directly related to molecular structure and bonding. The major development since 1965 in spontaneous, c.w. Raman spectroscopy has been the observation and exploitation by chemists of the resonance Raman effect. This advance, pioneered in chemical applications by Long and Loehr (15a) and by Spiro and Strekas (15b), overcomes the inherently feeble nature of normal (nonresonant) Raman scattering and allows observation of Raman spectra of dilute chemical systems. Because the observation of the resonance effect requires selection of a laser wavelength at or near an electronic transition of the sample, developments in resonance Raman spectroscopy have closely paralleled the increasing availability of widely tunable and line-selectable lasers. 

Resonance Raman Spectroscopy. If the excitation wavelength is chosen to correspond to an absorption maximum of the species being studied, a 102—104 enhancement of the Raman scatter of the chromophore is observed. This effect is called resonance enhancement or resonance Raman (RR) spectroscopy. There are several mechanisms to explain this phenomenon, the most common of which is Franck-Condon enhancement. In this case, a band intensity is enhanced if some component of the vibrational motion is along one of the directions in which the molecule expands in the electronic excited state. The intensity is roughly proportional to the distortion of the molecule along this axis. RR spectroscopy has been an important biochemical tool, and it may have industrial uses in some areas of pigment chemistry. Two biological applications include the determination of helix transitions of deoxyribonucleic acid (DNA) (18), and the elucidation of several peptide structures (19). A review of topics in this area has been published (20). 

For any vibrational mode, the relative intensities of Stokes and anti-Stokes scattering depend only on the temperature. Measurement of this ratio can be used for temperature measurement, although this application is not commonly encountered in pharmaceutical or biomedical applications. Raman scattering based on rotational transitions in the gas phase and low energy (near-infrared) electronic transitions in condensed phases can also be observed. These forms of Raman scattering are sometimes used by physical chemists. However, as a practical matter, to most scientists, Raman spectroscopy means and will continue to mean vibrational Raman spectroscopy. 

Heather, R.W. and Metiu, H. (1989). Time-dependent theory of Raman scattering for systems with several excited electronic states Application to a H3" model system, J. Chem. Phys. 90, 6903-6915. 

Advanced functional inorganic nanoparticles (NPs) have been studied intensively in the last couple of decades due to their unusual chemical and physical properties compared with their bulk materials, which enable them to be promising in applications as diverse as electronics,1 optics,2 optoelectronics,3 nanosensors,4 information storage,5 fuel cells,6 biomedicine,7 biological labeling,8 gene delivery,9 electrocatalysis,10 and surface enhanced Raman scattering (SERS).11,12 For instance, metal NPs with... 

Vibrational optical activity (VOA) is a relatively new area of natural optical activity. It consists of the measurement of optical activity in the spectral regions associated with vibrational transitions in chiral molecules. There are two basic manifestations of VOA. The first is simply the extension of electronic circular dichroism (CD) into the infrared region where fundamental one-photon vibrational transitions are located. This form of VOA is referred to as vibrational circular dichroism (VCD). It was first measured as a property of individual molecules in 1974 [1], and was independently confirmed in 1975 [2]. Within the past twelve years, VCD has been reviewed on a number of occasions from a variety of perspectives [3-15], and two more reviews are currently in press [16,17], The second form of VOA has no direct analog in classical forms of optical activity. Optical activity in Raman scattering, known simply as Raman optical activity (ROA), was measured successfully for the first time in 1973 [18], and confirmed independently in 1975 [19], ROA has been described in detail and reviewed several times in the past decade from several points of view [20-24], and two additional reviews [25,26], one with a view toward biological applications [25] and the other from a theoretical perspective [26], are currently in press. In addition, two articles of a pedagogical nature are in press that have been written for a general audience, one on infrared CD [27] and the other on ROA [28],... 

The first measurements of ROA followed by approximately five years the application of commercially available lasers to the measurement of Raman scattering spectra. More than any other technical advance, the laser light source elevated Raman scattering from the status of a curious alternative to infrared absorption to that of a powerful research tool. As will be discussed below, the processing of electronic data in ROA is much simpler than it is for VCD. In Raman scattering and ROA, spectral detection involves the conversion of scattered photons to individual electronic pulses that can be counted and stored. The main complication associated with the detection of ROA is the need to keep track of two separate bins of photon counts, one associated with RCP Raman intensity and the other with the corresponding LCP intensity. When the measurement is complete, the counts in the two bins are added to obtain the parent Raman spectrum and subtracted to obtain the ROA. 

As with VCD, the first ROA instruments were built around single-channel scanning dispersive spectrometers [18,19,76,77], Photomultipliers with dualchannel photon-counting electronics were used to record the spectra. Scanning rates were no faster than 1 cm l per minute because of the requirement to accumulate at least 10 7 counts per spectral location, and preferably 10 . Applications with these instruments were limited to samples with favorable Raman scattering and the goals of these early studies were simply to explore the nature of ROA spectra and to improve measurement techniques. Several reviews... 

Figure 15 (A) Diagrammatic representation of Raman process responsible for C-term resonance scattering. The applicable electronic...

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