Raman Scattering Cross Sections Research Articles

Orbital wave in the Raman scattering cross section of LaMnO3

We calculated the polarization-dependent Raman scattering cross section spectra of LaMnO3 below the A-type magnetic ordering temperature. Two strong peaks appear around the MnO6 octahedra stretching phonon frequency. One mode shows Ag symmetry, while the other mode shows Bg symmetry. We found that the Ag symmetry peak is a Jahn-Teller phonon coupled to the orbital wave and the Bg symmetry peak is an orbital wave coupled to a Q2 phonon mode via the Jahn-Teller electron phonon coupling.

Validity of Measuring Metallic and Semiconducting Single-Walled Carbon Nanotube Fractions by Quantitative Raman Spectroscopy.

Although it is known that the Raman spectroscopic signature of single-walled carbon nanotubes (SWCNTs) is highly chirality dependent, using Raman spectroscopy with several laser excitations as a tool for quantifying fraction of either metallic or semiconducting nanotubes in a sample has become a widely used analytical method. In this work, using the electron diffraction technique as a basis, we have examined the validity of Raman spectroscopy for quantitative evaluation of metallic fractions (M%) in single-walled carbon nanotube samples. Our results show that quantitative Raman spectroscopic evaluations of M% by using several discrete laser lines, either by using integrated intensities of chirality-associated radial breathing modes (RBMs) or, as has been more commonly utilized in recent studies, by statistically counting the numbers of RBMs can be misrepresentative. Specifically, we have found that the occurrence numbers of certain types of RBMs in Raman spectral mapping depend critically on the diameter distribution, resonant coupling between transition energies and excitation laser energy, and the chirality-dependent Raman scattering cross sections rather than simply on the metallic and semiconducting SWCNT fractions. These dependencies are similar to those observed in the integrated intensities of RBMs. Our findings substantially advance the understanding of the proper use of Raman spectroscopy for carbon nanotube quantification, which is important for carbon nanotube characterization and crucial to guide research in SWCNT growth and their applications.

Influence of Intermolecular Coupling on the Vibrational Spectrum of Water.

Raman multivariate curve resolution (Raman-MCR) spectra obtained from pure and isotopically dilute water are used to probe the influence of intermolecular resonance couplings on water OH and OD stretch band shapes and intensities, in the absence of intramolecular coupling. Intermolecular resonant coupling is found to broaden and red-shift the OH stretch band of water, in qualitative agreement with the predictions of Yang and Skinner. The influence of intermolecular coupling is found to increase with decreasing temperature, and to increase the Raman scattering cross section of the OH stretch, but decrease the OD stretch cross section. Moreover, we find that intermolecular coupling slightly perturbs the vibrational spectra of water molecules surrounding HOD.

All-trans-β-carotene absorption shift and electron-phonon coupling modulated by solvent polarizability

Absorption, resonance Raman spectra are reported on all-trans-β-carotene dissolved in different polarizability solvents. The absorption spectra of all-trans-β-carotene are analyzed by Franck-Condon principle and the Huang-Rhys factors are calculated. With the increasing solvent polarizability, the Huang-Rhys factor and the electron-phonon coupling constant decrease, while the Raman scattering cross section increases. The red-shift of absorption would leads to an increasing spectral overlap with the laser excitation leading to an enhanced resonance effect. Through electron-phonon coupling, the ground state structure of all-trans-β-carotene will be modulated by the electronic transition and is assumed to lead to a modulation of energy flow. Results present insights on the solvent's polarizability dependence on electron-phonon coupling of carotenoid. This work is expected to be helpful for exploring the surrounding medium effects on the electronic transition and carbon‑carbon vibrations.

Minimum possible laser pulse duration for SRS

The minimum laser pulse duration for transient stimulated Raman scattering is shown to be limited as a consequence of nonlinear phase modulation of the laser and Stokes waves. It is determined by the ratio of the nonlinear refractive index to the spontaneous Raman scattering cross section.

Raman spectroscopic quantification of sulfur species in aqueous fluids: Ratios of relative molar scattering factors of Raman bands of H2S, HS−, SO2, HSO4−, SO42−, S2O32−, S3− and H2O at ambient conditions and information on changes with pressure and temperature

We determined ratios of relative molar scattering factors J (or j) of Raman bands of sulfur species in aqueous solutions at 22°C, 0.1MPa, specifically those of H2S(aq) at ~2590cm−1 (J2590), HS−(aq) at ~2570cm−1 (J2570), SO2(aq) at ~1150cm−1 (J1150), HSO4−(aq) at ~1050cm−1 (J1050), SO42−(aq) at ~980cm−1 (J980), and S2O32−(aq) at ~445cm−1 (J445) and of water (i.e. the bending mode at ~1640cm−1 (J1640) and the O–H stretching band at ~3400cm−1 (J3400)). From experiments at elevated temperatures using a hydrothermal diamond-anvil cell, we further estimated ratios of the relative molar scattering factor of the Raman band of S3−(aq) at ~535cm−1 (J535) for excitation at wavelengths of 473 and 532nm, and discussed the effect of the blue coloration caused by S3− on Raman spectroscopic analysis of sulfur speciation. Another experiment suggested a significant decrease in the Raman scattering cross section of the band of HSO4−(aq) at ~1050cm−1 with temperature. A systematic study on integrated ν1(SO4) and νS(OH) intensities and their ratio as function of temperature to 600°C and pressure to 2.02GPa for a 2.33mNa2SO4 solution revealed a relationship between hydrogen bonding and νS(OH) Raman scattering efficiency. Moreover, it demonstrated that the integrated νS(OH) intensity can be used with reasonable accuracy as internal standard but only if corrected for the response function of the spectrometer, the frequency and scattering factor and the theoretical temperature dependence of the Raman scattering efficiency from the Bose-Einstein factor. The results of our study can be used to obtain the sulfur speciation in Raman spectroscopic studies on aqueous fluids in natural samples and experiments.

Quantitative Determination of the Differential Raman Scattering Cross Sections of Glucose by Femtosecond Stimulated Raman Scattering.

Femtosecond stimulated Raman spectroscopy (FSRS) is a vibrational spectroscopy technique that has been used in a wide variety of applications: from transient vibrational signature tracking to amplifying weak normal Raman scattering signals. Presented here is an application of FSRS to quantify the differential Raman scattering cross sections (DRSCs) of glucose. In using FSRS to determine the DRSCs of multiple glucose vibrational modes, we demonstrate the applicability of both stimulated Raman loss (SRL) spectroscopy and stimulated Raman gain (SRG) FSRS. Using the two analogous FSRS techniques, SRG and SRL, we determine that the DRSCs of glucose excited at 514.5 nm range from a low of 5.0 ± 1.1 × 10-30 to a high of 8.9 ± 0.9 × 10-30 cm2 molecule-1 sr-1. This work establishes both the compatibility of SRL for measuring DRSCs and values for the DRSC of multiple vibrational modes of glucose.

Raman Under Water - Nonlinear and Nearfield Approaches for Electrochemical Surface Science.

Electrochemistry is re‐gaining attention among scientists because the complex interplay between electronic and chemical interfacial processes lies at the bottom of a broad range of important research disciplines like alternative energy conversion or green catalysis and synthesis. While rapid progress has been made in recent years regarding novel technological applications, the community increasingly recognizes that the understanding of the molecular processes that govern macroscopic device properties is still rather limited – which hinders a systematic and more complete exploration of novel material and functionality space. Here, we discuss advanced Raman spectroscopies as valuable analysis tools for electrochemists. The chemical nature of a material and its interaction with the environment is contained in the label‐free vibrational fingerprint over a broad energy range so that organic species, solid‐state materials, and hybrids thereof can be investigated alike. For surface studies, the inherently small Raman scattering cross sections can be overcome with advanced nonlinear or nearfield‐based approaches that provide signal enhancements between three and seven orders of magnitude, sufficient to detect few scatterers in nano‐confined spaces or adsorbate (sub)monolayers. Our article highlights how advanced Raman techniques with extreme chemical, spatial and temporal resolution constitute valuable alternative surface analysis tools and provide otherwise inaccessible information about complex interfacial (electro)chemical processes.

SERS Chemical Enhancement of Water Molecules from Halide Ion Coadsorption and Photoinduced Charge Transfer on Silver Electrodes

The surface-enhanced Raman scattering (SERS) signal of water is hard to be measured due to its very small Raman scattering cross section and weak adsorption on coinage metals, only electrochemical SERS spectra of water have been observed in electrode/electrolyte interfaces so far. Our present work focuses on the chemical enhancement from halide ions on SERS signals of water adsorbed on silver electrodes, by combining the metallic cluster model and hybrid density functional theory (DFT) calculations. The interfacial structures, binding interactions and the anion effect from different halides including chloride, bromide, and iodide ions have been analyzed and compared with experimental measurements in literatures. Then the excited states of halide ions modified active sites on roughened silver electrodes have been discussed. In particular, our time-dependent DFT (TD-DFT) calculations predicted that halide ions can form low-lying excited states of surface complexes, like the photon-induced charge transfer (P...

Energy scaling and extended tunability of terahertz wave parametric oscillator with MgO-doped near-stoichiometric LiNbO3 crystal.

A widely tunable, high-energy terahertz wave parametric oscillator based on 1 mol. % MgO-doped near-stoichiometric LiNbO3 crystal has been demonstrated with 1064 nm nanosecond pulsed laser pumping. The tunable range of 1.16 to 4.64 THz was achieved. The maximum THz wave output energy of 17.49 μJ was obtained at 1.88 THz under the pump energy of 165 mJ/pulse, corresponding to the THz wave conversion efficiency of 1.06 × 10-4 and the photon conversion efficiency of 1.59%, respectively. Moreover, under the same experimental conditions, the THz output energy of TPO with MgO:SLN crystal was about 2.75 times larger than that obtained from the MgO:CLN TPO at 1.60 THz. Based on the theoretical analysis, the THz energy enhancement mechanism in the MgO:SLN TPO was clarified to originate from its larger Raman scattering cross section and smaller absorption coefficient.

Temperature effect on the resonance Raman spectra of all-trans-β-carotene in iodine solution

The resonance Raman spectra of the fundamental, combination, and second harmonic modes around the carbon–carbon single and double bonds stretches of all-trans-β-carotene in 1, 2-dichloroethane with iodine solution are obtained in the range of 293–83K. The Raman scattering cross section of the fundamentals in the liquid (293–213K) and solid phases (188–83K) increases as temperature decreases and the Raman bandwidths decreases. An intriguing phenomenon is that the Raman scattering cross section of the carbon-carbon single and double bonds in solution with iodine decreases and the Raman bandwidths increases, compared with the one without iodine. These phenomena are analyzed using the coherent weakly damped electron - lattice vibration mode.

Raman Imaging in Cell Membranes, Lipid-Rich Organelles, and Lipid Bilayers.

Raman-based optical imaging is a promising analytical tool for noninvasive, label-free chemical imaging of lipid bilayers and cellular membranes. Imaging using spontaneous Raman scattering suffers from a low intensity that hinders its use in some cellular applications. However, developments in coherent Raman imaging, surface-enhanced Raman imaging, and tip-enhanced Raman imaging have enabled video-rate imaging, excellent detection limits, and nanometer spatial resolution, respectively. After a brief introduction to these commonly used Raman imaging techniques for cell membrane studies, this review discusses selected applications of these modalities for chemical imaging of membrane proteins and lipids. Finally, recent developments in chemical tags for Raman imaging and their applications in the analysis of selected cell membrane components are summarized. Ongoing developments toward improving the temporal and spatial resolution of Raman imaging and small-molecule tags with strong Raman scattering cross sections continue to expand the utility of Raman imaging for diverse cell membrane studies.

Enhancement of Raman scattering from molecules placed near metal nanoparticles

Large Raman scattering cross sections from molecules on surfaces of metallic nanoparticles are described within a renormalization-group theory. In this approach the valence electrons of the molecules are embedded in an effective medium described by a dielectric function, which integrates out the effect of the plasmonic excitations of the metallic nanoparticles. The source of the enhanced photon inelastic scattering is produced by the resonant excitation of surface plasmons at the metallic nanoparticles. A similar theory has been successfully used to explain the resonant x-ray inelastic scattering and the behavior of nonlinear susceptibilities at the x-ray edges.

Temperature and salinity effects on the Raman scattering cross section of the water OH-stretching vibration band in NaCl aqueous solutions from 0 to 300 °C

Water is often used as an internal standard in quantitative Raman spectroscopic measurements of dissolved species in aqueous solutions containing salts at varying temperatures. However, the effects of temperature and dissolved ions on the relative differential Raman scattering cross section (RSCS) of the OH-stretching vibration band of water at elevated temperatures and salinities are not well defined quantitatively. In this study, the Raman spectra of NaCl solutions with different salinity (from 0 to 5 mol NaCl/kg · H2O) at 20 °C at atmospheric pressure and from 0 to 300 °C at 30 MPa were studied. The relative RSCS of the OH-stretching vibration band of liquid water (σ(mNaCl, T, 30 MPa)/σ(Pure water, 20 °C, 30 MPa)) as a function of temperature (T, in °C) and salinity (mNaCl, in mol/kg · H2O) was established: σmNaCl,T,30MPa/σ(Pure water,20oC,30MPa)=fT,mNaCl=aT−20+b where a = 0.000089 × mNaCl1/2 − 0.001164; b = 0.0355 × mNaCl + 1; The RSCS of the OH-stretching vibration band of water in pseudo back-scattering geometry decreases linearly with increasing temperature, but increases with the addition of dissolved NaCl within the whole temperature range. The enhancement factor of the RSCS by dissolved NaCl increases with temperature. Such effects of temperature and salinity should be considered in quantitative Raman spectroscopic study of species concentration in aqueous solution at high temperature when using water as internal standard. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of Fermi resonance of ν1 and 2ν2 on the Raman scattering of fundamental mode ν2 from liquid carbon disulfide

Raman scattering from liquid carbon disulfide has been studied for different concentrations in benzene. Modes ν1 (656cm−1) and 2ν2 (796cm−1) are allowed bands of carbon disulfide, while ν2 (396cm−1) is forbidden by the selection rules. However, a weak band has been observed along with the strong allowed totally symmetrical stretching mode ν1. The observation is ascribed to the effects of the vibrational anharmonicity of free molecule and intermolecular interaction potential. The ν1 and 2ν2 Fermi resonance can be influenced by the external conditions. The effects of the ν1 and 2ν2 Fermi resonance on the Raman frequency and relative intensity are discussed and the Raman scattering cross section of ν2 is studied for different concentration of carbon disulfide in benzene. The second-order perturbation quantum theory is introduced to explain the results that the Raman scattering of ν2 is influenced by 2ν2 and its Fermi resonance with ν1.

Determination of the thickness and orientation of few-layer tungsten ditelluride using polarized Raman spectroscopy

Orthorhombic tungsten ditelluride (WTe2), with a distorted 1T structure, exhibits a large magnetoresistance that depends on the orientation, and its electrical characteristics changes from semimetallic to insulating as the thickness decreases. Through polarized Raman spectroscopy in combination with transmission electron diffraction, we establish a reliable method to determine the thickness and crystallographic orientation of few-layer WTe2. The Raman spectrum shows a pronounced dependence on the polarization of the excitation laser. We found that the separation between two Raman peaks at ∼90 cm−1 and at 80–86 cm−1, depending on thickness, is a reliable fingerprint for determination of the thickness. For determination of the crystallographic orientation, the polarization dependence of the A1 modes, measured with the 632.8 nm excitation, turns out to be the most reliable. We also discovered that the polarization behaviors of some of the Raman peaks depend on the excitation wavelength as well as thickness, indicating a close interplay between the band structure and anisotropic Raman scattering cross section.

Water vapor pressure over molten KH2PO4 and demonstration of water electrolysis at ∼300 °C

A new potentially high-efficiency electrolyte for water electrolysis: molten monobasic potassium phosphate, KH2PO4 or KDP has been investigated at temperatures ∼275–325°C. At these temperatures, KH2PO4 was found to dissociate into H2O gas in equilibrium with a melt mixture of KH2PO4K2H2P2O7KPO3H2O. The water vapor pressure above the melt, when contained in a closed ampoule, was determined quantitatively vs. temperature by use of Raman spectroscopy with methane or hydrogen gas as an internal calibration standard, using newly established relative ratios of Raman scattering cross sections of water and methane or hydrogen to be 0.40±0.02 or 1.2±0.03. At equilibrium the vapor pressure was much lower than the vapor pressure above liquid water at the same temperature. Electrolysis was realized by passing current through closed ampoules (vacuum sealed quartz glass electrolysis cells with platinum electrodes and the electrolyte melt). The formation of mixtures of hydrogen and oxygen gases as well as the water vapor was detected by Raman spectroscopy. In this way it was demonstrated that water is present in the new electrolyte: molten KH2PO4 can be split by electrolysis via the reaction 2H2O→2H2+O2 at temperatures ∼275–325°C. At these temperatures, before the start of the electrolysis, the KH2PO4 melt gives off H2O gas that pressurizes the cell according to the following dissociations: 2KH2PO4↔K2H2P2O7+H2O↔2KPO3+2H2O. The spectra show however that the water by virtue of hydrogen-bonding has a high affinity for remaining in the melt. The formed hydrogen and oxygen gasses were detected by means of the characteristic Raman gas-phase spectra.

Identification of Multiple Water-Iodide Species in Concentrated NaI Solutions Based on the Raman Bending Vibration of Water.

The influence of aqueous electrolytes on the water bending vibration was studied with Raman spectroscopy. For all salts investigated (NaI, NaBr, NaCl, and NaSCN), we observed a nonlinear intensity increase of the water bending vibration with increasing concentration. Different lasers and a tunable frequency-doubled optical parametric oscillator system were used to achieve excitation wavelengths between 785 and 374 nm. Focusing on NaI solutions, the relative enhancement of the water bending vibration was found to increase strongly with excitation photon energy, in line with a preresonance effect from the iodide-water charge-transfer transition. We used multivariate curve resolution (MCR) to decompose the measured Raman spectra of NaI solutions into three interconverting spectral components assigned to bulk water and water molecules interacting with one (X···H-O-H···O) and two (X···H-O-H···X) iodide ions (X = I(-)). The Raman spectrum of solid sodium iodide dihydrate supports the assignment of the latter. Using the MCR results, relative Raman scattering cross sections of 4.0 ± 0.6 and 14.0 ± 0.1 were calculated for the mono- and di-iodide species, respectively (compared to that of bulk water set to unity). In addition, it was found that at relatively low concentrations each iodide ion affects the Raman spectrum of roughly 22 surrounding water molecules, indicating that the influence of iodide extends beyond the first solvation shell. Our results demonstrate that the Raman bending vibration of water is a sensitive probe, providing new insights into anion solvation in aqueous environments.

Carbon Nanodot-Decorated Ag@SiO2 Nanoparticles for Fluorescence and Surface-Enhanced Raman Scattering Immunoassays.

A novel immunoassay protocol was demonstrated by the combination of fluorescent carbon nanodots (CNDs) and Ag@SiO2 surface-enhanced Raman scattering (SERS) tag nanoparticles into ensembles for a bifunctional nanoplatform. The CND-decorated Ag@SiO2 nanoparticles were constructed for sensitive fluorescence and SERS immunoassays. The silica shell thickness and amount of Ag@SiO2 nanoparticles were optimized for availability of strong fluorescence emission. The considerably large Raman scattering cross section of in situ-generated actual Raman reporter, 4,4'-dimercaptoazobenzene, from the apparent reporter p-aminothiophenol modified on the surfaces of Ag nanoparticles upon illumination of laser compensated for the reduction of SERS signals resulting from silica coating to a great degree. The antibody-modified bifunctional nanoparticles were captured by antibody-modified quartz slides in the presence of antigens in the sandwich structures for fluorescence and SERS immunoassays. The bifunctional nanoparticles could be used not only as bimodal probes for biodetection but also as bimodal tracers for bioimaging.

Frequency pulling and line-shape broadening in graphene Raman spectra by resonant Stokes surface plasmon polaritons

This Rapid Communication reports on the modulation of the position and linewidth of the $G$ and $2D$ Raman bands for monolayer graphene through coupling to surface plasmon polaritons (SPPs). It is shown that gold nanoresonators tuned to the graphene Stokes emission frequency, not the laser pump, broaden the $G$ and $2D$ peaks and shift them to lower wave numbers, in addition to enhancing the Raman scattering cross section. The variation of the band displacement and broadening with the SPPs' frequency demonstrates a strongly dispersive phenomenon, ruling out chemical, mechanical, and thermal mechanisms. It is believed that strong graphene-SPP coupling is responsible for the frequency pulling and line-shape broadening.