Raman active material

We also tried measurements to demonstrate that hot spots make significant contributions to surface enhanced Raman scattering [34]. For this purpose, the sample of nanoparticie assembly was doped with Raman active molecules by a spincoating method, and near-field excited Raman scattering from the sample was recorded. We adopted Rhodamine 6G dye as a Raman active material, which is... 

The technique of stimulated Raman scattering (SRS) has been demonstrated as a practical method for the simultaneous measurement of diameter, number density and constituent material of micrometer-sized droplets. 709 The SRS method is applicable to all Raman active materials and to droplets larger than 8 pm in diameter. Experimental studies were conducted for water and ethanol mono-disperse droplets in the diameter range of 40-90 pm. Results with a single laser pulse and multiple pulses showed that the SRS method can be used to diagnose droplets of mixed liquids and ensembles of polydisperse droplets. 

Raman active materials, percentages to ppm levels. Lower detection levels with surface enhanced methods but not generally used for process analysis. 

Of great interest to physical chemists and chemical physicists are the broadening mechanisms of Raman lines in the condensed phase. Characterization of tliese mechanisms provides infomiation about the microscopic dynamical behaviour of material. The line broadening is due to the interaction between the Raman active chromophore and its environment. 

Plenary 14. A K Ramdas et al, e-mail address akr phYsics.purdue.edu (RS). Electronic RS studies of doped diamond as potential semiconducting materials. A Raman active Is (p3 2) ls (Pi/2 transition of a hole... 

An interesting variation of Raman spectroscopy is coherent anti-Stokes Raman spectroscopy (CARS) (99). If two laser beams, with angular frequencies CO and CO2 are combined in a material, and if cjj — is close to a Raman active frequency of the material, then radiation at a new frequency CJ3 = 2cJ2 — may be produced. Detection of this radiation can be used to characterize the material. Often one input frequency is fixed and the other frequency, from a tunable laser, varied until matches the Raman frequency. CARS has the capabiHty for measurements in flames, plasmas, and... 

Surface active material, 79, 81 Surface characterization, 45, 46 Surface coverage, 37 Surface enhanced Raman scattering, 45 Surface tension, 23, 25... 

It is important to appreciate that Raman shifts are, in theory, independent of the wavelength of the incident beam, and only depend on the nature of the sample, although other factors (such as the absorbance of the sample) might make some frequencies more useful than others in certain circumstances. For many materials, the Raman and infrared spectra can often contain the same information, but there are a significant number of cases, in which infrared inactive vibrational modes are important, where the Raman spectrum contains complementary information. One big advantage of Raman spectroscopy is that water is not Raman active, and is, therefore, transparent in Raman spectra (unlike in infrared spectroscopy, where water absorption often dominates the spectrum). This means that aqueous samples can be investigated by Raman spectroscopy. 

As the laser beam can be focused to a small diameter, the Raman technique can be used to analyze materials as small as one micron in diameter. This technique has been often used with high performance fibers for composite applications in recent years. This technique is proven to be a powerful tool to probe the deformation behavior of high molecular polymer fibers (e.g. aramid and polyphenylene benzobisthiazole (PBT) fibers) at the molecular level (Robinson et al., 1986 Day et al., 1987). This work stems from the principle established earlier by Tuinstra and Koenig (1970) that the peak frequencies of the Raman-active bands of certain fibers are sensitive to the level of applied stress or strain. The rate of frequency shift is found to be proportional to the fiber modulus, which is a direct reflection of the high degree of stress experienced by the longitudinally oriented polymer chains in the stiff fibers. 

The nonresonant contributions pertain to electron cloud oscillations that oscillate at the anti-Stokes frequency but do not couple to the nuclear eigenfrequencies. These oscillatory motions follow the driving fields without retardation at all frequencies. The material response can, therefore, be described by a susceptibility that is purely real and does not depend on the frequencies of the driving fields. The resonant contributions, on the other hand, are induced by electron cloud oscillations that are enhanced by the presence of Raman active nuclear modes. The presence of nuclear oscillatory motion introduces retardation effects relative to the driving fields i.e., there is phase shift between the driving fields and the material oscillatory response. 

Polyethylene has been studied spectroscopically in greater detail than any other polymer. This is primarily a result of its (supposedly) simple structure and the hope that its simple spectrum could be understood in detail. Yet as simple as this structure and spectrum are, a satisfactory analysis had not been made until relatively recently, and even then significant problems of interpretation still remained. The main reason for this is that this polymer in fact generally contains structures other than the simple planar zig-zag implied by (CH2CH2) there are not only impurities of various kinds that differ chemically from the above, but the polymer always contains some amorphous material. In the latter portion of the material the chain no longer assumes an extended planar zig-zag conformation, and as we have noted earlier, such ro-tationally isomeric forms of a molecule usually have different spectra. Furthermore, the molecule has a center of symmetry, which as we have seen implies that some modes will be infrared inactive but Raman active, so that until Raman spectra became available recently it was difficult to be certain of the interpretation of some aspects of the spectrum. As a result of this work, and of detailed studies on the spectra of n-paraffins, it now seems possible to present a quite detailed assignment of bands in the vibrational spectrum of polyethylene. 

Raman spectroscopy is an inelastic scattering technique that probes the vibrational energy levels within molecules and was first reported by C.V. Raman, who was awarded the Nobel Prize in Physics in 1930 for his discoveries. Nowadays, Raman spectroscopy is an established technique and is regularly used to analyze chemicals and materials, often in combination with infrared absorption spectroscopy since the two techniques are mutually complementary, that is, vibrational transitions that are Raman active are not IR active. In Raman scattering, light interacts with a molecule... 

Instead of SNOM, in many cases, particularly if the sample is to be screened for Raman active spots and their spatial distance is more than half of the wavelength of the laser, it is also confocal Raman microscopy that delivers enough morphological and spectral information on both nanoparticle structure and SERS activity, respectively. Thus, confocal Raman microscopy is interesting for a wide variety of applications in biology, medicine, and technological materials research. 

Sajanlal PR, Pradeep T (2009) Mesoflowers a new class of highly efficient surface-enhanced Raman active and infrared-absorbing materials. Nano Res 2(4) 306—320... 

In general, several Raman-active modes may be excited simultaneously by the ISRS excitation pulses and may contribute to coherent scattering of the probe pulse. The dielectric response tensor G (q, t) may be written as a sum of terms representing different material modes. In addition, depending on the polarizations used, several tensor components of G (q, t) may be sampled in a given experiment. For simplicity, we write... 

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