Structural characterization, Raman spectroscopy

Raman spectroscopy is primarily a structural characterization tool. The spectrum is more sensitive to the lengths, streng ths, and arrangement of bonds in a material than it is to the chemical composition. The Raman spectmm of crystals likewise responds more to details of defects and disorder than to trace impurities and related chemical imperfections. 

With the microfocus instrument it is possible to combine the weak Raman scattering of liquid water with a water-immersion lens on the microscope and to determine spectra on precipitates in equilibrium with the mother liquor. Unique among characterization tools, Raman spectroscopy will give structural information on solids that are otherwise unstable when removed from their solutions. 

Raman spectroscopy is a very convenient technique for the identification of crystalline or molecular phases, for obtaining structural information on noncrystalline solids, for identifying molecular species in aqueous solutions, and for characterizing solid—liquid interfaces. Backscattering geometries, especially with microfocus instruments, allow films, coatings, and surfaces to be easily measured. Ambient atmospheres can be used and no special sample preparation is needed. 

Two kinds of tantalum-containing initial solutions were chosen according to their ionic complex structure. The first one contained mostly TaF6 ions (Ta F = 1 18) while the second was characterized predominantly by TaF72 ions (Ta F = 1 6.5). The ionic composition of the solutions was determined by Raman spectroscopy. 

Well-defined CdS/CdSe superlattices have been formed by means of ECALE [74]. In these structures the CdS component - and not CdSe - suffered from substantial crystallographic strain as was evidenced by surface-enhanced Raman spectroscopy (SERS) - a valuable tool for characterizing the superlattice phonons in electrochemical or other ambient environments. Torimoto et al. reported quantum confinement in superlattices of ZnS/CdS grown by ECALE [75]. 

Raman spectroscopy A nondestructive method for the study of the vibrational band structure of materials, which has been extensively used for the characterization of diamond, graphite, and diamond-like carbon. Raman spectroscopy is so far the most popular technique for identifying sp bonding in diamond and sp bonding in graphite and diamond-like carbon. 

The functionalization of zinc porphyrin complexes has been studied with respect to the variation in properties. The structure and photophysics of octafluorotetraphenylporphyrin zinc complexes were studied.762 Octabromoporphyrin zinc complexes have been synthesized and the effects on the 11 NMR and redox potential of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraarylporphyrin were observed.763 The chiral nonplanar porphyrin zinc 3,7,8,12,13,17,18-heptabromo-2-(2-methoxyphenyl)-5,10,15,20-tetraphenylporphyrin was synthesized and characterized.764 X-ray structures for cation radical zinc 5,10,15,20-tetra(2,6-dichlorophenyl)porphyrin and the iodinated product that results from reaction with iodine and silver(I) have been reported.765 Molecular mechanics calculations, X-ray structures, and resonance Raman spectroscopy compared the distortion due to zinc and other metal incorporation into meso dialkyl-substituted porphyrins. Zinc disfavors ruffling over doming with the total amount of nonplanar distortion reduced relative to smaller metals.766 Resonance Raman spectroscopy has also been used to study the lowest-energy triplet state of zinc tetraphenylporphyrin.767... 

Vibrational spectroscopy techniques are quite suitable for in situ characterization of catalysts. Especially infrared spectroscopy has been used extensively for characterization of the electrode/solution interphases, adsorbed species and their dependence on the electrode potential.33,34 Raman spectroscopy has been used to a lesser extent in characterizing non-precious metal ORR catalysts, most of the studies being related to characterization of the carbon structures.35 A review of the challenges and applications associated with in situ Raman Spectroscopy at metal electrodes has been provided by Pettinger.36... 

In the last century, many microstructural characterization techniques have been developed, such as electron microscopy, atomic tunneling microscopy, photoelectron spectroscopy, Raman spectroscopy, etc. The structure of the OLED-based displays is such that many pixels are arranged orderly in the x-y plane. The size and number of pixels determine the resolution and size of the display. Along the z-axis, several layers are stacked on each other. These layers... 

Raman spectroscopy has been used by several authors as an indent-ification method by comparing spectra of solutions with spectra of solid phases of known structure (85, 92-95). The heptamolybdate could be clearly identified (cf. below) and its spectrum in the solid state and aqueous solution is well characterized (93, 94). Other polyanions seem to be more difficult to identify because overlapping equilibria tend to conceal small changes in the spectrum upon acidification. 

Raman spectroscopy offers an alternative for the vibrational characterization of catalysts, and has been used for the study of the structure of many solids, in particular of oxides such as Mo03, V205,... 

Further details of the theory and application of Raman spectroscopy in polymer studies can be found elsewhere (1. 9). However, vibrational frequencies of functional groups in polymers can be characterized from the spacing of the Raman lines and thus information complementary to IR absorption spectroscopy can be obtained. In addition, since visible radiation is used the technique can be applied to aqueous media in contrast to IR spectroscopy, allowing studies of synthetic polyelectrolytes and biopolymers to be undertaken. Conformation and crystallinity of polymers have also been shown to influence the Raman spectra Q.) while the possibility of studying scattering from small sample volumes in the focussed laser beam (-100 pm diameter) can provide information on localized changes in chemical structure. 

Raman spectroscopy is one of the most powerful techniques for the characterization of nanocarbons. It is also a convenient technique because it involves almost no sample preparation and leaves the material unharmed. There are four characteristic bands for CNTs The band at 200 cm-1 is called radial breathing mode (RBM). It depends on the curvature and can be used to calculate the diameter of SWCNTs [61]. The relatively broad D-band at 1340 cm-1 is assigned to sp2-related defects and disorder in the graphitic structure of the material. The tangential C-C stretching mode is located at -1560 cm 1 (G-band). The second order mode of the D-band can be observed (G -band,... 

Suitable characterization techniques for surface functional groups are temperature-programmed desorption (TPD), acid/base titration [29], infrared spectroscopy, or X-ray photoemission spectroscopy, whereas structural properties are typically monitored by nitrogen physisorption, electron microscopy, or Raman spectroscopy. The application of these methods in the field of nanocarbon research is reviewed elsewhere [5,32]. 

---