Raman Bandwidth Research Articles

Raman bandshape analysis on C[sbnd]H and CSC stretching modes of dimethyl sulfoxide in liquid binary mixture: Comparative study with quantum-chemical calculations

The interacting nature of dimethyl sulfoxide (DMSO) in binary mixtures has been carried out on CH and CSC stretching modes of vibration using chloroform (CLF), chloroform-d (CLFd), acetonitrile (ACN) and acetonitrile-d3 (ACNd) solvents. Peak frequencies of both the stretching modes show blue shift with the increase in solvent concentration. Variation of Raman bandwidth with the solvent concentration was discussed using different mechanisms. Ab initio calculation for geometry optimization and vibrational wavenumber calculation have been performed on monomer and dimer structures of DMSO to explain the experimentally observed Raman spectra. Theoretically calculated values are found in good agreement with the experimental results. Vibrational and reorientational relaxation times have been studied corresponding to solvent concentrations to elucidate the interacting mechanisms of binary mixtures.

Compositional and thermal treatment effects on Raman gain and bandwidth in nanostructured silica based glasses

Investigations of new materials possessing both higher Raman gain and larger spectral bandwidth than fused silica are becoming mandatory in order to satisfy increasing telecommunications demands. Herein, silica–niobia based glasses have been prepared and characterized by ellipsometry and Raman spectroscopy. A fine glass structural characterization of bulk system has been performed and the Raman gain has been quantified. Our silica-based glass system (K2O–Nb2O5–SiO2 (KNS)) provides via thermal treatment a nanocomposite material of easy and cheap fabrication. In our glass composition a strong Raman gain (up to 30 times higher than fused silica) and a large bandwidth have been measured and demonstrated to be related to nanostructured material domains.

Reversible Loss of Bernal Stacking during the Deformation of Few-Layer Graphene in Nanocomposites

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (∼0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed.

Improvement of Raman amplifier bandwidth by means of slow light in photonic crystal based waveguide structure

In this paper, we investigate the enhancement of Raman amplification bandwidth with self phase modulation (SPM) effect in silicon based photonic crystal waveguides. The Maxwell equations are solved using finite difference time domain method considering two photon absorption, free carrier absorption, Kerr and SPM effects. We also study the effects of shape, width and average power on the Raman amplification bandwidth. Then by changing the photonic crystal geometrical parameters, pump and signal group velocity are reduced to achieve higher Raman bandwidth.

X-ray diffraction, atomic force microscopy and raman spectroscopy studies of microstructure of BiFeO3 thin films on Pt/Ti/SiO2/Si (111) substrates

A set of BiFeO3 (BFO) thin films with different thicknesses deposited on Pt/Ti/SiO2/Si (111) substrates and LaNiO3 (LNO)-buffered Pt/Ti/SiO2/Si (111) substrates using a radio-frequency magnetron sputtering technique was studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and Raman spectroscopy. The XRD patterns demostrated that all BFO thin films were polycrystalline with a distorted rhombohedral structure even though there were distinct changes in the main peak positions and intensities. The AFM topography images also clearly illustrated the different surface profiles of these thin films. The grain size of thin films deposited on LNO-buffered subtrates was greatly decreased compared to that of thin films deposited directly on Pt/Ti/SiO2/Si (111) substrates. Raman-active modes, which can be classified as 4A 1 and 9E modes, have been observed in the Raman spectra of the BFO thin films. Variations in the Raman shift and bandwidth of different BFO thin films reveal the influence of the thin film and buffer layer thicknesses on the film microsturcture.

Study on Raman Spectra of Zinc Gluconate under Effect of Different Solvent

Raman spectrum is a kind of characteristic spectrum. The information of molecular vibration and rotation can be obtained by studying Raman spectrum. Raman spectrum will be changed because of molecular interaction under effect of different solvent. We selected zinc gluconate as the object of research. Zinc gluconate is dissolved respectively in ethyl chloride, benzene, ring of ethane，chloroform, acetic acid, ethylene oxide, n-propanol, n-butanol solution, and Raman spectra were tested. The change of molecular internal structure and the interaction of molecular functional groups are studied by means of measuring Raman frequency shift, bandwidth, and light intensity. Thus, the information of solute structure change can be obtained. Experiments show that when zinc gluconate dissolved in the organic solvent, molecular gap became larger, its velocity increased, and stretching vibration of associating OH key group became strong. Methylenes in polar and non-polar molecule interact, and the polarization changed. In different polar solvents, Raman spectra had different changes. When the bond length increases，the stretching vibration frequency of molecules moves to the direction of low frequency. It produces red shift instead of blue shift. The results of this paper provide a basis to study molecular interactions further.

Compositional effect of WO3, MoO3, and P2O5 on Raman spectroscopy of tellurite glass for broadband and high gain Raman amplifier

In order to obtain broadband and high Raman gain coefficient in the tellurite glass, a detailed study of the effects of WO3, MoO3, and P2O5 in TeO2-ZnO-Na2O-Nb2O5 (TZNN) glass system on the thermal stabilities and Raman spectroscopic was performed. It was found that both WO3 and MoO3 improved the glass thermal stability and enhanced the bandwidth significantly. Higher Raman gain coefficients and broader bandwidth were realized in the MoO3 modified glasses than those of WO3 added glass. The tellurite glass containing 15 mol. % MoO3 exhibits the bandwidth 1.7 times larger than the silica glass and the Raman gain coefficient is as high as 38 times that of the silica glass. Moreover, with the addition of P2O5 in TeO2-ZnO-Na2O-Nb2O5-WO3 (TZNNW) and TeO2-ZnO-Na2O-Nb2O5-MoO3 (TZNNM) glass systems, the thermal stabilities can further be improved. On the other hand, the Raman bandwidth can further be broadened, especially in the TZNNMP glass system. The tellurite glass containing 15 mol. % MoO3 and 15 mol. % P2O5 shows the bandwidth 1.9 times larger than the silica glass and maintains high Raman gain coefficient which is as high as 37 times that of the silica glass, indicating this glass is a promising candidate as new gain media for broadband Raman fiber amplifier.

Temperature Dependence of the Raman Intensity and the Bandwidth Close to the Order-Disorder Phase Transition in NaNO<sub>3</sub>

We analyze the temperature dependence of the Raman intensity using the experimental data according to a power-law formula close to the order-disorder transition (Tc = 549 K) in NaNO 3. From this analysis, we extract the value of β = 0.26 as the critical exponent for the order parameter, which indicates a tricritical phase transition in this crystalline system. Using the temperature dependence of the order parameter, the Raman bandwidth is calculated at various temperatures in NaNO3. Our calculated bandwidths describe adequately the observed behaviour of the order-disorder transition in this crystal.

Silica under hydrostatic pressure: A non continuous medium behavior

The homogeneous/inhomogeneous structure of glasses is still a debated question. Hydrostatic high pressure experiments allow us to determine if a glass behaves as an elastic continuous random network or if a nanometer scale heterogeneity has to be taken into account. In order to get information on the homogeneous/inhomogeneous structure of glasses, in situ high pressure Raman experiments are performed on silica in the elastic domain up to 4.7 GPa. A strong decrease of the Boson peak intensity is observed between 1 bar and 3 GPa. We show that this decrease does not correspond quantitatively to the effect of pressure on a homogeneous elastic medium. From the interpretation of the narrowing of the main Raman band width under pressure as a narrowing of the θ inter-tetrahedral Si–O–Si angle distribution it is shown that the decrease of the Boson peak intensity is correlated to the decrease of the intrinsic inhomogeneity of the silica glass. These results confirm the occurrence of an intrinsic inhomogeneity at a nanometer scale even in a single component glass like SiO 2 which is very important for the interpretation of the optical or mechanical properties of the glasses.

Metamictization in zircon: Raman investigation following a Rietveld approach. Part II: Sampling depth implication and experimental data

AbstractProfile line deconvolution following a Rietveld approach is applied to Raman spectra obtained from natural zircon grains from the European Alps. The corrected bandwidths are in perfect agreement with the values obtained from an established correction method (after Irmer) as far as the area of validity of the latter is concerned. For Raman active modes smaller than that, the Rietveld approach also yields accurate values for the true Raman bandwidth. Moreover, changes to instrument parameters are compensated by the correction routine. As for the studied zircon grains, Raman spectroscopy was shown to be a suitable tool for the examination of zoning (i.e. regions which show a variable degree of radiation‐induced damage because of a different amount of incorporated uranium and/or thorium). This is complicated by the fact that the measured Raman signal is not restricted to the depth expected from the axial resolution (several micrometers) but a significant contribution comes from a comparatively large excitation volume (tens of micrometer deep). This sampling volume, however, lies within the same order of magnitude as zoning, which itself is blurred by the range of amorphization‐causing alpha‐particles. Copyright © 2008 John Wiley & Sons, Ltd.

Metamictization in zircon. Part I: Raman investigation following a Rietveld approach: Profile line deconvolution technique.

AbstractThe line profile form of Raman spectra can be analyzed using the very same approach and software used for diffractogram deconvolution via the Rietveld approach. In both cases the ‘true’ profile containing information about the sample must be separated from the instrument's profile function (and potentially from the emission profile) which can be achieved by deconvolution. In this first part of a two‐part study we demonstrate how the instrument's function can be described via a Gaussian function profile (yielding the very same result as several convoluted hat functions) using several examples (diamond, calcite, silicon and silicon carbide) for which true Raman bandwidth values are presented (assuming the true band profile to be Lorentzian). Also, asymmetrical bands can be described and analyzed via the presented deconvolution approach. The second part of this study will discuss and apply this method for studying the radiation‐induced damage in zircon grains (metamictization). Copyright © 2008 John Wiley & Sons, Ltd.

Structure properties of BiFeO3 films studied by micro-Raman scattering

BiFeO 3 (BFO) films deposited on SrTiO3 (001) substrates and on LaNiO3-coated SrTiO3 (001) substrates with different annealing ambiences of oxygen and nitrogen were studied by using micro-Raman spectroscopy and x-ray diffraction (XRD). XRD showed that the films are in single-phase with rhombohedral structure. According to the analysis of the group theory, 13 Raman-active modes, which can be classified as 4A1 and 9E modes, have been observed in the BiFeO3 films. Raman spectra along the growth direction of the BFO films in the side-view scattering geometry were performed by the Raman mapping technique. The variations of Raman shift and Raman bandwidth in different depths of the films imply the existence of residual strain along the growth direction of the BFO films. These results are very useful for the understanding of the depth dependence of the physical properties including the interface and surface structure of the BFO films.

Raman scattering characteristics of the TBSN-based tellurite glass system as a new Raman gain medium

A study was initiated to understand requirements for widening and flattening the gain spectra of tellurite-based glasses for their application as new gain media for photonic devices. For this purpose, two Raman active components, WO3 and P2O5, were added either separately or jointly to a TeO2-BaO-SrO-Nb2O5 (TBSN) glass system, and the Raman spectral evolution in response to this addition was studied. Raman scattering cross sections of the TBSN glasses were increased with an increase in the WO3 content and decreased with an increase in the P2O5 content. The Raman intensity and bandwidth increased when WO3 and P2O5 were jointly added in TBSN. The bandwidths of the Raman gain coefficient spectra of the present tellurite glasses were more than twice that of a conventional TeO2-Bi2O3-ZnO-Na2O glass and 70% larger than that of silica glass. The new glasses are expected to be candidates for ultrabroadband fiber Raman amplifiers.

Enhancement of Structural Fluctuation in the Region Connecting Two Kinds of Critical Points in Temperature−Pressure−Composition Three-Dimensional Phase Diagram: Raman Studies of Benzene/CO2 Binary Systems up to Supercritical Region

Pressure dependence of Raman spectra of benzene/CO2 two-component systems was systematically studied at different temperatures and compositions. We estimated the magnitude of inhomogeneous component in Raman bandwidth to get information on the structural fluctuation in the system. It was found that the inhomogeneous bandwidth attains a maximum on an isothermal plane in the temperature-pressure-composition three-dimensional phase diagram when the state point crosses the line connecting the region where the density fluctuation is large (the vicinity of the critical point of neat CO2) and the region where the concentration fluctuation in a binary system is enhanced (the vicinity of the critical solution point). By accumulating such data, we found that the points of large structural fluctuation comprise a sheet that includes the extension line of the gas-liquid equilibrium line in the phase diagram of neat CO2 and the line connecting critical solution points of the two-component system at different temperatures. Interaction between benzene and CO2 molecules in the supercritical region is briefly discussed.

An opportunity for directly estimating the characteristics of zero-point dynamics in polyethylene crystals

For large polyethylene crystallites (100 × 60 × 60 nm), the width of the Raman band at 1129 cm−1 and the angular position of the x-ray equatorial 110 reflection were measured as a function of temperature over the range 5–300 K. It is found that the Raman bandwidth has an athermic (zero-point) component at low temperatures. This component is used to estimate the zero-point energies of torsional and bending vibrations of polyethylene molecules. These energies are close to those obtained from analyzing the x-ray diffraction data. It is concluded that the characteristics of zero-point dynamics can be determined directly from measuring the zero-point width of a Raman band.

Depth profiling of strain and defects in Si∕Si1−xGex∕Si heterostructures by micro-Raman imaging

We have reported depth and in-plane profiling of strain, Ge composition, and defects in strained-Si∕Si1−xGex∕Si heterostructures using micro-Raman imaging. Raman profiling in the depth direction was carried out with a depth resolution of ∼15nm using a small-angle beveled sample and ultraviolet (UV) excitation. Depth profiles of the Ge composition and Raman bandwidth clearly show that the defect density depends strongly on the Ge-grading rate in a compositionally graded Si1−xGex layer. The in-plane strain variation at a given depth in each layer has been evaluated. The in-plane strain variations in the Si1−xGex are closely related to clustering of misfit dislocations in the graded Si1−xGex layer. For the top strained-Si layer, two-dimensional UV-Raman images of the frequency and bandwidth of the Si band reveal that film crystallinity is correlated with the magnitude of in-plane strain. The close correlation between the frequency and bandwidth is attributed to inhomogeneous strain fields associated with misfit dislocation clusters, which induce complete relaxation of strain in constant composition Si1−xGex layers.

Enhanced Raman gain coefficients and bandwidths in P2O5 and WO3 added tellurite glasses for Raman gain media

The Raman gain coefficient and bandwidth of tellurite glasses have been tailored by systematically adding WO3 and P2O5 in a TeO2–BaO–SrO–Nb2O5 glass system. The Raman gain coefficients of the resultant glasses were obtained from spontaneous Raman scattering experiments using a 633nm laser. The glasses developed here showed the widest gain bandwidths so far achieved in tellurite glasses while maintaining higher gain coefficients. The gain bandwidths of these glasses were more than twice that of a conventional tellurite-based glass and 70% larger than that of the silica glass.

Vibrational relaxation studies in methyl acetate: Role of microenvironment and hydrodynamic forces

The Raman spectra were recorded for the C O stretching vibration of methyl acetate as solutions in various polar and non-polar solvents. The isotropic component was obtained and the vibrational relaxation rates were calculated. On the basis of dependence of isotropic Raman bandwidth on the hydrodynamic properties of the solute–solvent systems, the information was obtained on the microenvironment prevailing in the neighborhood of the C O stretching mode. Significant correlation is observed between vibrational relaxation rate and solvent parameters namely viscosity, density, refractive index and molecular radius. Microviscosity, involving the size of solute and solvent molecules, is found to be crucial in determining the bandwidth, hence the relaxation rate. The microenvironment appears to play an important role in the vibrational relaxation process.

Anisotropy shift and Raman bandwidth studies in carbonyl containing molecule o-chlorobenzaldehyde: Role of repulsive forces

The analysis of Raman anisotropy shift as a function of solvent concentration shows the weakening of pair interaction of the molecules due to the influence of solvent-induced perturbations. The present study deals with the effect of dielectric constant of the medium on the non-coincidence effect (anisotropy shift) and the role of van der Waals’ volume on the anisotropic Raman bandwidth. The C O stretching vibration of o-chlorobenzaldehyde (OCBD) molecule was studied in various polar and non-polar solvents namely CCl 4, CH 3CN, C 6H 5Cl and CH 3C 6H 5. The data on anisotropic bandwidth are interpreted using the van der Waals’ volume within the framework of lineshape theory of Bratos and Tarjus, while the Onsager–Fröhlich model on non-coincidence effect has been tested. Our study shows that the repulsive potential of the type e −αR is playing an important role in the OCBD–solvent interactions. The vanishing of anisotropy shift (non-coincidence effect) on dilution may be explained on the basis of repulsive forces playing a significant role in solute–solvent interactions.

Size and phonon-confinement effects on low-frequency Raman mode of anatase TiO 2 nanocrystal

Raman spectra of anatase TiO 2 nanocrystals with 2.2–25.5 nm grain sizes were measured at temperature range 83–293 K. The size dependences of the frequency, the bandwidth and the lineshape of the low-frequency mode agree well with those calculated on the basis of the phonon confinement model with the theoretical phonon dispersion relationships. The correlations of both Raman frequency and bandwidth to the grain size L satisfy a L −1.3 law. The contributions of three-phonon anharmonic processes to the frequency and bandwidth at various grain sizes were obtained from the temperature dependence of the Raman spectra, and the results show that the phonon coupling is increased in anatase TiO 2 nanocrystal.