Low-frequency Raman Research Articles

Nanostructures in glasses probed by low-frequency raman scattering

The interest of low-frequency Raman scattering for the study of materials at the nanometric scale is demonstrated. The linear dependence between the Raman shift and the inverse of the diameter of the nanostructures makes it a good tool to follow the kinetic of growth of crystalline inhomogeneities in semi-conductor quantum dots or in precursors of glass ceramics. In glasses it appears as one of the few ways to investigate medium-range order and suggests a non-continuous structure. Extension towards the study of phase transformations in semi-conductor nanostructures or the evolution of the medium range order structure of glass with fictive temperature is in progress (Chemarin et al., 1997).

Low-Frequency raman scattering and structural range order in Na2O–PbO–Bi2O3–P2O5 phosphate glasses

Systematic studies of the low-frequency Raman scattering (LFRS) in Na2O-PbO-Bi2O3-P2O5 phosphate glasses have been undertaken. In the continuum media approximation, these studies, permit one to find out the structural correlation range Rc, and to determine the structural correlation function. The estimated correlation lengths from the LFRS supports the concept that the scale for structural order in the studied glasses is ∼ 7 A.

Chain direction elastic modulus of PE crystal and interlamellar force constant ofn-alkane crystals from RAMAN measurements

Spectroscopic data can deliver force constants only if the exact chain conformation is known. For the longitudinal acoustic modes (LAM), however, simple linear chain models can be used to yield the effective longitudinal chain modulus from spectroscopic data of oligomer crystals. The model of p-coupled linear chain molecules with N masses and only nearest neighbor interactions was used to investigate the longitudinal acoustic modes with s nodes. The frequencies plotted versus s/N fall onto different branches for different s. The intermolecular coupling and the heavier endmasses shift the LAM branches to higher and lower frequencies, respectively. There exists a value x0 depending on the masses and force constants, where the branches cut the dispersion curve of the infinite molecule. For s/N ≥ x0 the effect of endmasses dominates. Low-frequency RAMAN spectra of n-alkanes (N = 20, …, 40 C atoms) were recorded and analyzed. The LAM1 branch runs clearly above a smooth fit through all other LAM data and the origin. This fit approximates to first order the dispersion curve of the infinite PE molecule in an ideal crystal. Its curvature exceeds that of the dispersion curve of the simple linear chain, but is somewhat smaller than that of the dispersion curve of the planar zig-zag chain with rigid bonds. The slope at the origin yields the limiting elastic modulus Ec = 315 GPa in chain direction of crystalline polyethylene. From our measurements on n-alkanes we obtained the frequency shift of LAM1 due to the interlayer coupling and the heavier endmasses. Calculation of the intermolecular coupling constant of the model of a long row of linear chain molecules with the same frequency shift yield the mean value fl = 2.5 N/m. This value decreases with increasing chain length. The relevance and applicability of the model is discussed. © 1997 John Wiley & Sons, Inc.

Effects of resonance on low-frequency raman scattering from semiconductor nanocrystals

Abstract An investigation of Raman scattering in CdSe nanocrystals embedded in oxide glass matrix under resonant excitation has been accomplished. First we observe the dependence of both the longitudinal optical phonon and the low frequency scattering energies with the excitation wavelength which is explained in terms of size selective excitation. A peculiar attention is given to the behaviour of low-frequency spectra and selection rules due to resonance effects are reported. Most of the first harmonics of the different predicted vibration modes have been observed and a qualitative attempt has been made to link the observed modes with the excited electronic levels.

Order-disorder-liquid transition of KNO3studied by raman scattering

Abstract Low-frequency Raman scattering spectra of potassium nitrate, KNO3 are observed as a function of temperature in a range from room temperature up to 130 K above the melting point Tm (606 K), including its order-disorder phase transition point at 403 K (Tc ). A central peak grows drastically with increasing temperature below and above Tm . Numerical analysis of the spectra reveals two spectral components; one is characteristic of the molten state even in the solid state below Tm , and the other is very sensitive for melting process. The former is caused by an orientationally disordered motion and the latter by a translational displacement motion of cation and anion indicating pre-melting phenomenon in the solid state phase by anomalous increase of damping.

Evidence of quantum‐size effect and electron–phonon interactions in resonance Raman scattering spectra of semiconductor nanocrystals

AbstractRaman spectra of II–VI semiconductor nanocrystals embedded in silicate glass matrices with near‐resonance and resonance excitation in the range of electron transitions between size‐quantized energy levels were studied. It is shown that only the transitions with angular momentum l = 0, 2 contribute to the resonance Raman enhancement. The influence of the electron–phonon interaction on the Raman excitation profiles of the LO phonons and elastic vibrations of nanocrystals is analysed. The effect of the matrix on the intensities and frequencies of the low‐frequency Raman (LFR) bands and the possibilities of determining the particle size determination using LFR spectra are discussed.

Low frequency raman modes in polypyrrole polymers

Low frequency Raman scattering from fractal vibrational modes in polypyrrole is investigated. The polypyrrole was prepared by the chemical and electrochemical method, and the polypyrrole obtained was characterized by the infrared spectrum and X-ray diffraction. The experimental results show the broad band distribution between 30 and 140 cm −1 and the Raman peak at 65,77,116 cm −1 for exciting line with 5145 Å were observed. According to the fractal theory, we point out for the first time that the low frequency Raman spectra may be from localized fractal vibrational mode in polypyrrole molecule chian with the intensity of the Raman light scattering expressed as a function of frequency shift, fractal and spectral dimensions. The fraction dimension is estimated according to the experimental data. The Raman spectra are well explained in terms of a fraction description of localized vibrations.

Interactions in macromolecular solutions manifested by the mobility of solvent molecules in the low-frequency raman range

The results of investigations on the effect of macromolecular interactions in dilute solutions upon the mobility of solvent molecules, observed in the low frequency Raman range ( 8 cm −1 < δ v 50 cm −1 ), are reported. Both polarized (VV) and depolarized (VH) components of the scattered light were measured in order to detect the joint effect of the correlated anisotropy fluctuations and intermolecular vibrations. Three frequency ranges were observed in the spectra, characterized by different relaxation times attributed to different types of the solvent molecules mobility. The effect of the structure of polymer side groups on the increase in the relaxation time, τ 1, measured in the range 8 < δ v < 30 cm −1 was observed. These interactions are considerably weaker in solutions of polyetherester with a rigid backbone than those occurring in solutions of flexible macromolecules with mesogenic side groups.

Effect of annealing temperature on TiO2 monolayer thin films as studied by waveguide raman spectroscopy and electron microscopy

The crystallographic form of TiO 2 is only anatase in the temperature range studied. The very low-frequency Raman scattering provided the mean diameter of the particles, which correspondded with electron microscopy results. The progression of this mean diameter is demonstrated.

Низкочастотные спектры КР некоторых метилзамещенных компонентов нуклеиновых кислот: 9-метилпроизводные пуриновых оснований

Низкочастотные спектры КР некоторых метилзамещенных компонентов нуклеиновых кислот: 9-метилпроизводные пуриновых оснований

Низкочастотные спектры КР некоторых метилзамещенных компонентов нуклеиновых кислот: 1-метилпроизводные пиримидиновых оснований

Низкочастотные спектры КР некоторых метилзамещенных компонентов нуклеиновых кислот: 1-метилпроизводные пиримидиновых оснований

Низкочастотные фононные спектры КР света компонентов нуклеиновых кислот: пиримидиновые основания

Низкочастотные фононные спектры КР света компонентов нуклеиновых кислот: пиримидиновые основания

A unique low frequency raman band associated with metal binding to metallothionein

We find that the low frequency Raman spectrum of Zn(II) metallothionein has a single prominent band at 138 cm-1 which is absent from the Raman spectrum of the metal-free protein. This feature is also found for Cd(II) binding to both of the independent metallothionein domains and the metallothionein from Neurospora crassa. TcO(III) coordination to metallothionein results in a similar Raman band which is also found for the complex (Ph4As)[ReO(SCH2CH2S)2]. By comparing these results to literature data for metal-thiolate complexes, this feature is identified as a bending vibration which appears to be characteristic of metal ion coordination by the metallothionein cysteines. Two likely assignments are a symmetric metal-centered mode (delta S-M-S) or a bending mode of the metal-coordinated cysteine thiolates (delta M-S-C).

Low-frequency raman scattering on surface vibrational modes of microcrystals

Low-frequency peaks have been observed in Raman spectra of nucleated glasses. A phenomenological model is proposed for their explanation. The data obtained from the analysis of Raman spectra are compared with the results of small-angle X-ray scattering. It is shown that the low-frequency Raman spectra permit to determine conditions at the boundaries, sizes and concentrations of structure microinhomogeneities in disordered materials.

Hydrogen bonding in liquid amides studied by low frequency raman spectroscopy.

Low frequency Raman spectra (10–400 cm −1) in the R( ν )-representation are used to investigate N-ethylformamide in the liquid state. Polarization measurements are performed. Spectra are also obtained of Nd0ethylformamide. The results are compared to similar investigations of formamide, N-methylformamide and N,N-dimethylformamide, acetamide, N-methylacetamide and N,N-dimethylacetamide. A band observed around 100 cm −1 is assigned to vibrations of atoms in intermolecular hydrogen bonds of chain-like species. An approximate description of this mode is given.

Pressure dependence of the low-frequency raman spectra of 4,4'-difluorobenzophenone and 4,4'-dibromobenzophenone

The low-frequency Raman spectra as a function of hydrostatic pressure for 4,4'-difluorobenzophenone and 4,4'-dibromobenzophenone are presented. The change observed in some of the Raman bands suggests that the pressure induces changes in the crystal structure.

Low frequency raman scattering of As 2S xSe 3−x

Low frequency (< 60 cm −1) Raman spectra have been measured for a series of chalcogenide glasses and crystals of the form As 2S xSe 3−x. Comparison of the spectra of x = 0 and x = 0.5 of the crystals clearly establishes the rigid layer (RL) mode character of the peaks near 21 and 31 cm −1 and the admixture of RL and intralayer modes for the series of peaks near 50 cm −1. The observed lineshape of the glasses is interpreted in terms of a density of states of optic modes.

ChemInform Abstract: OBSERVATION OF TWO OXYGEN‐ISOTOPE SENSITIVE BANDS IN THE LOW‐FREQUENCY RESONANCE RAMAN SPECTRUM OF OXY(PHTHALOCYANATO)IRON(II)

Chemischer InformationsdienstVolume 16, Issue 11 Physical Organic Chemistry ChemInform Abstract: OBSERVATION OF TWO OXYGEN-ISOTOPE SENSITIVE BANDS IN THE LOW-FREQUENCY RESONANCE RAMAN SPECTRUM OF OXY(PHTHALOCYANATO)IRON(II) K. BAJDOR, K. BAJDORSearch for more papers by this authorH. OSHIO, H. OSHIOSearch for more papers by this authorK. NAKAMOTO, K. NAKAMOTOSearch for more papers by this author K. BAJDOR, K. BAJDORSearch for more papers by this authorH. OSHIO, H. OSHIOSearch for more papers by this authorK. NAKAMOTO, K. NAKAMOTOSearch for more papers by this author First published: March 19, 1985 https://doi.org/10.1002/chin.198511044AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue11March 19, 1985 RelatedInformation

Low frequency raman scattering in plastic crystals

In this paper we were concerned with the informations provided by the analysis of the low frequency Raman scattering in plastic crystals involving two aspects of the rotational dynamics : The librational dynamics and the reorientational dynamics. Three typical behaviours of low frequency Raman spectra are given. A comparison with neutron scattering data is made.

Experimental studies of long life phonons in molecular crystals by high resolution raman spectroscopy

Using an interferometer-spectrometer in tandem with a limiting resolution of 0.005 cm-1 we have measured the band profiles of some low frequency Raman active phonons of monoclinic tetracyanoethylene (TCNE) and α-glycine at low temperature. In this latter case we obtained by deconvolution of the observed profiles residual bandwidths at T = 0 K as small as 0.004 cm-1 for two lattice phonons.The observed bandwiths are interpreted in terms of three-phonon decay processes and the most important relaxation mechanisms are determined. Correlation of the bandwidths with the one-and two-phonon density of states is used to localize the frequency range where decay into two acoustic phonons of the same energy is the dominant relaxation process.The present results are compared with those obtained previously for other molecular crystals such as naphthalene, anthracene and l-alanine. It is shown that at a given frequency the phonon bandwidths of the hydrogen bonded crystals are at least one order of magnitude smaller than those of the normal Van der Waals crystals. This effect is interpreted as due to the different anharmonicity of the intermolecular potential in the two cases.The evolution with temperature of the phonon bandwidths has been followed for α-glycine in the range 5-50 K. An excellent fit of the experimental data is obtained assuming a maximum of two preferential up-conversion decay mechanisms.