The structural independence of Raman scattering cross sections of ν1(NO3−) and ν(H2O)

The Raman scattering cross section (RSCS) is an important parameter in the applications of Raman spectroscopy to make quantitative analysis. To date, the dependence of the RSCS on concentration has remained unclear. Nitrate aerosols can easily achieve a supersaturated state, which provides a way to obtain the RSCS especially under this state. In this study, Raman spectra of NaNO₃ and Mg(NO₃)₂ solutions are obtained with molar water‐to‐solute ratios (WSRs) ranging from 84.2 to 2.30 and 93.8 to 7.32, respectively. With decreasing WSR, a shift to higher wavenumbers of the symmetric stretching band of nitrate ion, i.e. ν₁(NO₃⁻), is observed, indicating the formation of various ion pairs. Meanwhile, the area ratio between the strongly and weakly hydrogen‐bonded components of water O H stretching envelope, i.e. ν(H₂O), reduces as the WSR decreases, implying the transformation of water molecules from strong hydrogen‐bonding structures to the weak ones. However, a good linear relationship is revealed between the integrated intensity ratio of the ν(H₂O) band to ν₁(NO₃⁻) band and WSR. The results suggest that the RSCSs of NO₃⁻ and H₂O are insensitive to the structures of both ion pairs and hydrogen‐bonding structures. This observation points to the possibility of conducting quantitative analysis through the area ratio of the ν(H₂O) band to the ν₁(NO₃⁻) band with Raman spectra without considering the formation of ion pairs and the variation of the hydrogen‐bonding structure. Copyright © 2011 John Wiley & Sons, Ltd.     

Picosecond stimulated Raman scattering of BaWO4 crystal

In single-pass configuration, a picosecond pulse laser was used to investigate the stimulated Raman scattering in different BaWO₄ crystals. Using the thresholds for the first Stokes line along the a- and c-axis, the Raman gain coefficients of the BaWO₄ crystals were calculated along their respective direction. The higher Stokes (fourth) and anti-Stokes (third) lines were observed. Compared with other well-known Raman crystals, such as KGd(WO₄)₂ and Ba(NO₃)₂, BaWO₄ has favorable properties for scattering the pump radiation with picosecond pulse duration. The Raman gain coefficients of BaWO₄ are different, but do not vary for different transmission directions, which means that this Raman material can be selected more freely.     

RING EFFECT: IMPACT OF ROTATIONAL RAMAN SCATTERING ON RADIATIVE TRANSFER IN EARTH’S ATMOSPHERE

One significant limitation to the accuracy of the remote sensing of trace gas constituents in the atmosphere, using UV-visible spectroscopy and scattered sunlight, has often been a reliable knowledge of the so-called Ring effect. In this study it is demonstrated that the filling-in of Fraunhofer and gas absorption features, resulting from Rotational Raman scattering (RRS), explains to high accuracy the Ring effect. A radiative transfer model has been adapted to include RRS and carefully validated by comparison with Ring effect data by other models and from ground-based and satellite data. The analysis of the principle components of the simulated Ring spectra enabled the Fraunhofer and gas absorption filling-in to be separated. This yields a simple, and therefore computational fast, parameterization of the Ring effect suitable for trace gas retrievals. This approach was tested for the retrieval of NO₂ which is considered to be a worst case with respect to absorption feature filling-in for a trace gas retrieved from scattered light. Analysis of the errors in the vertical column of NO₂ derived using differential optical absorption spectroscopy (DOAS) technique indicate that they are dependent on the amount of NO₂ present in the atmosphere when regarding the experimental Ring spectra. This implies that calculated Ring spectra may be superior for DOAS retrievals, compared to the experimentally determined Ring spectra.     

镶嵌在SiO2薄膜中InAs纳米颗粒的Raman散射

对镶嵌在SiO₂薄膜中纳米InAs颗粒的Raman散射谱进行了研究.与大块InAs晶体相比,InAs纳米颗粒的Raman散射谱具有相似的特征,即由纵光学声子模和横光学声子模组成,但是散射峰宽化并红移.用声子限域效应解释了散射峰的红移现象,并结合InAs纳米颗粒的应力效应解释了红移量与理论值的差异. 关键词： 2薄膜')" href="#">SiO₂薄膜 InAs量子点 Raman散射     

Raman Scattering Intensities of the NO2 Symmetric Stretching Vibration Band of Some Aromatic Nitrocompounds (II)

The Raman scattering intensities of the NO₂ symmetric stretching vibration band were investigated experimentally for some para and meta substituted nitrobenzenes. The excitation profiles obtained with the six excitation wavelengths from 457.9 to 514.5 nm were presented. The results were examined in terms of the Albrecht-Hutley's theory, and the electronic states involved in the preresonance Raman intensity enhancement were suggested.     

Analysis of residual stresses in ternary electroconductive composites

Residual stresses in ceramic particle electroconductive composites were investigated by Raman microprobe spectroscopy and X-ray diffraction. The composites were ternary electroconductive ceramics in the system AlN+SiC+(ZrB₂,MoSi₂). Due to the poor definition of the reinforcing phase peaks, only the matrix residual stress could be evaluated by Raman spectroscopy, whilst the residual stress in the reinforcing phase was calculated by the equilibrium conditions. These calculated values were compared with those experimentally obtained by X-ray diffraction. The agreement between Raman and X-ray results was quite satisfactory. The values of residual stress calculated by the composite theory were in good agreement with those measured by Raman and X-ray diffraction for the MoSi₂-containing composite. For the ZrB₂-containing composite, the value calculated by the composite theory falls between the values measured by Raman and X-ray diffraction. PACS 81.05.Je; 87.64.Je; 87.64.Bx     

Synthesis of Ge nanocrystals by atom beam sputtering and subsequent rapid thermal annealing

Ge nanocrystals embedded in an SiO₂ matrix were prepared by the atom beam co-sputtering (ABS) method from a composite target of Ge and SiO₂. The as-deposited films were rapid thermally annealed at the temperatures 700 and 800 °C in nitrogen ambience. The structure of the films was evaluated by using X-ray diffraction (XRD) and Raman spectroscopy. XRD results reveal that as-deposited films are amorphous in nature whereas annealed samples show crystalline nature. Raman scattering spectra showed a peak of Ge–Ge vibrational mode shifted downwards to 297 cm^?1, presumably caused by quantum confinement of phonons in the Ge nanocrystals. Rutherford backscattering spectrometry has been used to measure the thickness and Ge composition of the composite films. Size variation of Ge nanocrystals with annealing temperature has been discussed. The advantages of ABS over other methods are highlighted.     

Dynamics of molecules excited by infrared laser radiation

The CF₂HCl and CF₂Cl₂ molecules upon multiphoton excitation are investigated by the method of Raman light scattering spectroscopy at frequencies of fundamental transitions. It is demonstrated that essentially nonequilibrium energy distribution of molecules is formed in the process of excitation. Physical parameters characterizing this distribution are determined.     

Evidence for oxygen abstraction from NO<Subscript>2</Subscript> upon thermal scattering from an Al(111) surface

Evidence is presented for the existence of a non-adiabatic reaction channel, namely the abstraction of an oxygen atom from a nitrogen dioxide molecule upon scattering from an aluminium(111) surface. This reaction channel was studied by exposing the sample to an NO₂ molecular beam and subsequently analysing the scattered flux using REMPI spectroscopy. In these experiments, a considerable amount of NO emitted from the surface was detected. The emitted NO has a rotational temperature of ca. 260 K that increases only slowly with surface temperature. In summary, these results provide first evidence for the abstraction reaction NO_2(g)NO_(g)+O_(a) upon NO₂/Al(111) scattering, which may arise when two electrons are rapidly transferred to the incoming molecule while it is unfavourably oriented for concurrent adsorption of both fragments. PACS 82.65.+r; 68.43.-h     

Electronic state of MgB2 superconductor

Thanks to the high quality single crystals of MgB₂, we have measured various physical properties to extract important features of the electronic state in this superconductor. The electron density maps calculated from a precise X-ray diffraction analysis and the band dispersions determined by the angle-resolved photoemission spectroscopy demonstrate that the boron orbitals play a central role, just as predicted by the band theory. The strong coupling of the high frequency optical phonon with the boron bands is indicated in resistivity and Raman scattering spectra. Although the multi-band structure significantly affects various normal state properties, no clear multi-gap feature can be observed in the Raman scattering spectra below T_c.     

Electric field modulated Raman scattering in CdS

We have observed electric field modulated Raman scattering by A₁ LO phonons in CdS. The field induced scattering is observed with a geometry in which Raman scattering by A₁ LO phonons is normally allowed. The interference of the field induced and allowed terms in the transition susceptibility leads to a modulated Raman scattering intensity proportional to the applied field. This is contrasted with data previously reported on field induced Raman scattering by E₁ LO phonons in a configuration in which the Raman scattering is normally forbidden and in which there is no interference between linear wavevector dependent and field induced terms in the transition susceptibility. Electric field effects on Raman scattering by TO phonons and by 2 LO phonons is also discussed.     

Luminescent properties of Yb-doped monoclinic yttrium polyphosphates

Yb³⁺-doped monoclinic yttrium polyphosphate Y(PO₃)₃ powder compounds were synthesized and were characterized by X-ray diffraction, IR absorption spectroscopy and Raman scattering spectroscopy.An attempt to use Yb³⁺ ion as structural probe is carried out to investigate the site occupation. Yb³⁺ emission and fluorescence decay studies were carried out both at low and room temperatures. The interpretation of electronic energy level positions has been done by using the comparison of emission spectra with those of vibronic sideband energy positions from Raman scattering spectroscopy.The spectroscopic results are discussed and correlated with the data of the already known monoclinic structure of Y(PO₃)₃ where four slightly different octahedral sites are available for the trivalent rare earth ion.     

Temporal characteristics of picosecond stimulated Raman scattering in oxide crystals

The temporal characteristics of stimulated Raman scattering (SRS) under 22-ps laser excitation were studied in eight oxide crystals with a T ₂ optical-phonon dephasing time variable by up to two orders of magnitude. The measured SRS pulse width was shortened from 13.8 ps for Ba(NO₃)₂ (T ₂ = 26.5 ps) to 4 ps for the LiNbO₃ (T ₂ = 0.38 ps) crystal. The dependence of SRS pulse width on the dephasing time was analyzed in the framework of the known SRS theory.     

Nonlinearity in Intensity versus Concentration Dependence for the Deep UV Resonance Raman Spectra of Toluene and Heptane

Abstract: The relation between Raman scattering, resonance Raman scattering, and absorption is reviewed to determine to what extent quantitative analysis can be applied in resonance Raman spectroscopy. In addition, it is demonstrated experimentally that normal Raman spectra can be dramatically inhibited by absorption and resonance Raman effects. Raman spectra of toluene and heptane mixtures—with progressively increasing concentrations of heptane—were measured using 229-nm laser excitation. The results show that the characteristic band intensities are not directly proportional to the relative concentrations of the compounds and deviate due to absorption resonance effects. An approximated mathematical model is developed to demonstrate that the intensities of the normal Raman scattering bands are suppressed. An inhibition coefficient K_i is introduced to describe the situation and determine the penetration depth. Most remarkably, it is shown that the intensity of the resonance Raman scattering bands can be constant even when the concentration ratios differ substantially in the sampled mixtures.     

Investigation of structural phase transition in polycrystalline SrTiO3 thin films by Raman spectroscopy

Polycrystalline SrTiO₃ thin films were prepared by pulsed laser deposition technique. The phonon properties and structural phase transition were studied by Raman spectroscopy. The first-order Raman scattering, which is forbidden in SrTiO₃ single crystal, has been observed in the films, due to the structural distortion caused by strain effect and oxygen vacancies. The Fano-type line shape of TO₂ phonon reveals the existence of polar microregions in the STO thin films. The evolution of TO₂ and TO₃ phonons with temperature shows the occurrence of a structural phase transition at 120 K related to the formation of polar macroregions in the films.     

Resonant Raman scattering in the superconducting cuprates: Frozen-phonon versus perturbational approach

We consider in detail Raman scattering by vibration of the apical oxygen ions in the RBa₂Cu₃O₇ superconducting cuprates. The scattering intensity is very sensitive to the ratio of diagonal and off-diagonal matrix elements of electron-phonon coupling, bandstructure, and carrier concentration. Our results show a large quantitative difference between the results of frozen-phonon and perturbational approach to the Raman process. The discrepancy becomes especially large when interband transitions to the states near the Fermi level are close to resonance with the incident light. The calculation of phonon-induced ion charge fluctuations shows an analogous discrepancy. The reason for these effects is the possibility of carrier redistribution between different parts of the Fermi surface arising in the frozen-phonon approximation. Our results show that Raman scattering in superconducting superlattices is very sensitive to the properties of the states near the Fermi level. For this reason experiments performed on the superlattices can help to resolve the discrepancy. Received 8 December 1999     

Hydrothermal synthesis of 3D Cu0.45Mn0.55O2 nanostructures; lattice vibrations and novel photoluminescence properties

In this paper, Novel 3D Cu_0.45Mn_0.55O₂ nanoarchitectures self-assembled by interconnecting densely stacked nanosheets have been successfully synthesized by facile hydrothermal growth method. The crystalline phase, morphology, particle size and component of the as-prepared nanomaterial were characterized by X-ray diffraction, field-emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy and Raman spectroscopy. FESEM analysis shows that the size of 3D Cu_0.45Mn_0.55O₂ nanostructures is in the range of 1–1.5 μm, and the thickness of interconnected nanosheets is about 45 nm on the average. The structural features of as-synthesized Cu_0.45Mn_0.55O₂ nanostructures are studied to analyze the near-neighbor environment of oxygen coordination around manganese and copper cations reported for the first time using Raman scattering spectroscopy. Moreover, the novel photoluminescence spectra of the as-prepared Cu_0.45Mn_0.55O₂ nanostructures are reported exhibiting prominent emission bands located in red-violet spectral region.     

Photoluminescence of GeO<Subscript>2</Subscript> films containing germanium nanocrystals

Germanium nanocrystals were formed in a GeO₂ film during the process of germanium monoxide gas-phase deposition onto a sapphire substrate and studied by photoluminescence (PL) and Raman scattering spectroscopy. A PL peak in this heterosystem was observed in the visible region at room temperature. The sizes of Ge nanocrystals were estimated from the position of a Raman peak corresponding to scattering by localized optical phonons in germanium. The PL peak position calculated with allowance for the electron and hole size quantization in Ge nanocrystals coincides well with the experimentally observed position of this peak.     

Synthesis of DLC films by PLD from liquid target and dependence of film properties on the synthesis conditions

DLC (Diamond-like carbon films) were prepared by pulsed laser ablation of a liquid target at substrate temperatures from 18 to 600°C using 248 nm KrF excimer laser. The sp³ hybridization state carbon formation was additionally promoted by gaseous H₂O₂ flow through the reaction chamber and substrate excitation by the same laser beam. Deposited DLC films were characterised by Raman scattering spectroscopy and atomic force microscopy (AFM). Comparative AFM and Raman study shows that the increase in the content of sp³ type bonding in DLC is in correlation with the increase of the surface roughness of the samples prepared.