Raman-active Bands Research Articles

Synthesis and photovoltaic property characterization of CeO2 film deposited on ITO substrate for dye sensitized solar cell

The photoanodes of the dye sensitized solar cell (DSSC) were designed using nanocrystalline cerium oxide (CeO2) film. In this study the CeO2 photoanodes were obtained on ITO substrate using two different growth times such as 12 and 24 h by hydrothermal process. The prepared photoanodes and their characteristic performances towards solar energy conversion to electric power have been investigated. The grown photoanodes exhibited the cubic fluorite crystal structure with (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (4 0 0) planes and the corresponding selected area electron diffraction ring pattern of the HR-TEM confirms the growth of high purity nanocrystalline CeO2 films. The room temperature LASER Raman spectrum indicates the formation of cubic phase at 456 cm−1, the Raman active F2g band. From HR-SEM analysis agglomerated sphere particles in Ce-24 h and individual spherical particles in Ce-12 h infers the degree of super saturation which plays an important role in crystal nucleation and growth time. The DSSC assembled with dye sensitized CeO2 photoanodes have shown 1.201 and 0.931% of conversion efficiency at 1Sun (100 mW/cm2) AM1.5G solar illumination for Ce-12 h and Ce-24 h samples respectively. In our study the Ce-12 h photoanode exhibit efficiency greater than Ce-24 h due to increased dye absorption over the CeO2 nanoparticle surface.

Characterisation of the Chemical Composition and Structural Features of Novel Antimicrobial Nanoparticles.

Three antimicrobial nanoparticle types (AMNP0, AMNP1, and AMNP2) produced using the TesimaTM thermal plasma technology were investigated and their compositions were determined using a combination of analytical methods. Scanning electron micrographs provided the morphology of these particles with observed sizes ranging from 10 to 50 nm, whilst FTIR spectra confirmed the absence of polar bonds and organic impurities, and strong Raman active vibrational bands at ca. 1604 and 1311 cm−1 ascribed to C–C vibrational motions were observed. Carbon signals that resonated at δC 126 ppm in the solid state NMR spectra confirmed that sp2 hybridised carbons were present in high concentration in two of the nanoparticle types (AMNP1 and AMNP2). X-ray powder diffraction suggested that AMNP0 contains single phase Tungsten carbide (WC) in a high state of purity and multiple phases of WC/WC1-x were identified in both AMNP1 and AMNP2. Finally, X-ray photoelectron spectral (XPS) analyses revealed and quantified the elemental ratios in these composite formulations.

Tracking Intramolecular Vibrational Redistribution in Polyatomic Small-Molecule Liquids by Ultrafast Time–Frequency-Resolved CARS

Selective excitation of C-H stretching vibrational modes, detection of intramolecular vibrational energy redistribution (IVR), and vibrational modes coupling in the electronic ground state of benzene are performed by using femtosecond time- and frequency-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy. Both of the parent modes in the Raman-active bands are coherently excited by an ultrafast stimulated Raman pump, giving initial excitations of 3056 cm-1 (A1g) and 3074 cm-1 (E2g) and subsequent IVR from the parent modes to daughter modes of 1181 and 992 cm-1, and the coherent vibrational coupling of the relevant modes is tracked. The directionality and selectivity of IVR and coherent coupling among all of the relevant vibrational modes are discussed in the view of molecular symmetry.

Temperature-induced strain release via rugae on the nanometer and micrometer scale in graphene monolayer

Wrinkles are one possible rugae phase that can be observed in two-dimensional crystals. Those topographic features, with dimensions ranging from nanometers to micrometers, can be identified in single-layer graphene transferred onto various substrates. When the temperature of the sample is varied, the different thermal expansion coefficients of graphene and its supporting substrate lead to reconstruction of the graphene's topography, which results in spatially inhomogeneous strain and doping. Using Raman spectral mapping, we investigated in situ the temperature dependence (50–300 K) of topographic features in a graphene monolayer grown by chemical vapor deposition (CVD) and transferred onto a Si/SiO2 substrate. We find that the temperature-induced strain follows the temperature variation of the cubic lattice parameter of the Si substrate. Furthermore, the temperature-induced strain has an unambiguous relation to the topographic reconstruction of the graphene monolayer. We focused on the behavior of two types of rugae: 1) large wrinkles with dimensions that are larger than the laser spot size and can be traced directly and 2) nanoscale wrinkles and ripples, which can be identified by changes in the parameters of the principal Raman active bands of the graphene monolayer. In addition, we observed that temperature-induced reconstructions are accompanied by local variation of doping.

Critical slowing of quantum atomic deuterium/hydrogen with features of multiferroicity in the geometrically frustrated system Co2(OD)3Cl/Co2(OH)3Cl

An extensive study of hydroxyl salts $\mathrm{C}{\mathrm{o}}_{2}{(\mathrm{OD})}_{3}\mathrm{Cl}/\mathrm{C}{\mathrm{o}}_{2}{(\mathrm{OH})}_{3}\mathrm{Cl}$ utilizing muon-spin-relaxation (\ensuremath{\mu}SR), nuclear magnetic resonance (NMR), and Raman spectroscopy, supplemented by dielectric constant and magnetic susceptibility measurements, has revealed a unique multiferroic system with deuterium-order-type ferroelectricity and geometrically frustrated magnetism. Through the temperature-dependent dynamics of the nuclear fields probed by \ensuremath{\mu}SR, the deuterium atoms in $\mathrm{C}{\mathrm{o}}_{2}{(\mathrm{OD})}_{3}\mathrm{Cl}$ were found to be rapidly fluctuating in the paraelectric phase. Upon cooling, they showed a critical slowing down toward the ferroelectric transition at ${T}_{c}\phantom{\rule{4pt}{0ex}}={T}_{\ensuremath{\varepsilon}}=230\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, below which eight new Raman-active phonon bands appeared as a result of symmetry breaking due to deuterium ordering. Meanwhile, the hydrogen atoms in $\mathrm{C}{\mathrm{o}}_{2}{(\mathrm{OH})}_{3}\mathrm{Cl}$ became quasistatic at a reduced temperature near 210 K, wherein only one new Raman band appeared with a broad dielectric anomaly, suggesting incomplete ordering. Furthermore, the \ensuremath{\mu}SR, NMR, Raman spectroscopy, and the magnetic susceptibility all suggested an increase in magnetic couplings below $\ensuremath{\sim}250\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in both $\mathrm{C}{\mathrm{o}}_{2}{(\mathrm{OD})}_{3}\mathrm{Cl}$ and $\mathrm{C}{\mathrm{o}}_{2}{(\mathrm{OH})}_{3}\mathrm{Cl}$, demonstrating a multiferroic feature for $\mathrm{C}{\mathrm{o}}_{2}{(\mathrm{OD})}_{3}\mathrm{Cl}$. This work presents a new and unique multiferroic system with an exceptional high ${T}_{\mathrm{c}}$. It also demonstrates that conventional \ensuremath{\mu}SR can be an effective tool for studying ferroelectrics.

Enthalpy Differences of the n-Pentane Conformers.

The energy and enthalpy differences of alkane conformers in various temperature ranges have been the subject for both experimental and theoretical studies over the last few decades. It was shown previously for the conformers of butane [G. Tasi et al., J. Chem. Theory Comput. 2012, 8, 479-486] that quantum chemical results can compete with spectroscopic techniques and results obtained even from the most carefully performed experiments could be biased due to the improper statistical model utilized to evaluate the raw experimental data. In the current study, on one hand, the experimental values and their uncertainties for the enthalpy differences for pentane conformers are re-evaluated using the appropriate statistical model. On the other hand, a coupled-cluster-based focal-point analysis has been performed to calculate energy and enthalpy differences for the conformers of pentane. The model chemistry defined in this study includes contributions up to the perturbative quadruple excitations augmented with further small correction terms beyond the Born-Oppenheimer and nonrelativistic approximations. Benchmark quality energy and enthalpy differences for the pentane conformers are given at temperatures 0 and 298.15 K as well as for the various temperature ranges used in the gas-phase experimental measurements. Furthermore, a slight positive shift for the experimental enthalpy differences is also predicted due to an additional Raman active band belonging to the gauche-gauche conformer.

High-pressure X-ray diffraction and Raman spectroscopy of CaFe2O4-type β-CaCr2O4

In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic studies of orthorhombic CaFe2O4-type β-CaCr2O4 chromite were carried out up to 16.2 and 32.0 GPa at room temperature using multi-anvil apparatus and diamond anvil cell, respectively. No phase transition was observed in this study. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields a zero-pressure volume of V 0 = 286.8(1) A3, an isothermal bulk modulus of K 0 = 183(5) GPa and the first pressure derivative of isothermal bulk modulus K 0′ = 4.1(8). Analyses of axial compressibilities show anisotropic elasticity for β-CaCr2O4 since the a-axis is more compressible than the b- and c-axis. Based on the obtained and previous results, the compressibility of several CaFe2O4-type phases was compared. The high-pressure Raman spectra of β-CaCr2O4 were analyzed to determine the pressure dependences and mode Gruneisen parameters of Raman-active bands. The thermal Gruneisen parameter of β-CaCr2O4 is determined to be 0.93(2), which is smaller than those of CaFe2O4-type CaAl2O4 and MgAl2O4.

Effect of crystallite size, Raman surface modes and surface basicity on the gas sensing behavior of terbium-doped SnO2 nanoparticles

In the present work, we report the structural, optical and gas sensing properties of Tb3+-doped SnO2 nanoparticles. XRD results confirmed tetragonal rutile structure of both undoped and Tb3+-doped SnO2 nanoparticles which was further confirmed from Raman results. The increase of dopant concentration resulted in decrease in crystallite size which has been confirmed from XRD and TEM results. Raman spectra exhibited bands positioned at 562 and 487cm−1 whose contribution has been found to increase with decrease in crystallite size. The shifting and broadening of Raman active bands has been explained by well-known phonon confinement model. EDS analysis inveterate presence of terbium in the doped SnO2 nanoparticles. It has been observed that 3% doped samples exhibited optimum sensor response towards ethanol vapor. The optimum operable temperature of doped samples has been reduced as compared to undoped samples. The enhanced sensor response of doped nanoparticles is attributed to the small crystallite size, high surface basicity and enhanced contribution of Raman surface vibration modes of nanoparticles.

Adsorption configuration of sodium 2-quinoxalinecarboxylate on iron substrate: Investigation by in situ SERS, XPS and theoretical calculation

The adsorption geometry of sodium 2-quinoxalinecarboxylate (2-QC) on iron surface was investigated by in situ surface-enhanced Raman scattering spectroscopy (SERS) and X-ray photoelectron spectroscopy (XPS) measurements. The density functional theory (DFT) calculations predicted that 2-QC ion was a highly efficient inhibitor and N as well as O atoms were the possible adsorption centers, and theoretically offered the Raman-active band position and intensity. Potential-dependent SERS results suggested that the 2-QC strongly bonded to the iron surface via the lone pair electrons of the two O atoms of the carboxylate group in a bidentate configuration with a vertical orientation at more positive potentials; However, at −1.0V, only one O atom of the carboxylate and the neighboring N1 atom (or very close to surface) adsorbed on the iron surface forming an unidentate configuration with a titled orientation. The ions did not remain on the iron surface at more negative potentials.

Structure and microwave dielectric properties of Ca0.66La0.387Ti0.88O3 ceramics

Ca0.66La0.387Ti0.88O3 microwave dielectric ceramics were prepared via a mixed oxide solid state sintering route and characterized. X-ray diffraction revealed the formation of single phase Ca0.66La0.387Ti0.88O3 ceramics with orthorhombic (Pbnm) symmetry within the detection limit of the in-house XRD facility. Raman spectroscopy revealed the presence of seven Raman active bands evident of orthorhombic symmetry, in agreement with the present X-ray diffraction results. The microstructure of sintered samples appeared almost dense with some occasional pores. Ca0.66La0.387Ti0.88O3 exhibited reasonable relative permittivity (~71.5) and quality factor (~13,407 GHz); however, its temperature coefficient of resonance frequency was high (~136.4 × 10−6/°C) for commercial applications and requires further optimization.

The assessment of the photocatalytic activity of magnetically retrievable ZnO coated γ-Fe2O3 in sunlight exposure

The photocatalytic activity of magnetically retrievable ZnO@γ-Fe2O3, synthesized by coating γ-Fe2O3, with ZnO in 5:1 and 10:1 ratio, was assessed for the mineralization of chlorophenol derivatives (2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-tri chlorophenol) and compared with that of pure ZnO in natural sunlight exposure. The diffuse reflectance spectroscopy revealed the composite nature of the synthesized catalysts with the existence of dual band edges representing ZnO and γ-Fe2O3. The decreased emission intensity in the photoluminescence (PL) spectra rendered the contributory role of γ-Fe2O3 in suppressing the charge carrier annihilation. The growth of Raman active bands of ZnO was observed with increasing density of coated layers. The morphology and structural changes were examined by XRD and FESEM. The cyclic voltammetric (CV) and electrochemical impedance spectroscopy (EIS) measurements, in the dark and under illumination, verified the elimination of photocorrosion and better trapping of the excited states in the synthesized coated catalysts as compared to pure ZnO. A noticeable increase in the degradation/mineralization ability, in comparison to pure ZnO, was observable for the ZnO coated on γ-Fe2O3 support. The progress of the photocatalytic degradation process was monitored by HPLC while the mineralization ability of the synthesized catalysts was estimated by TOC and measuring the release ions by ion chromatography (IC). Based on repeated precise weight measurements, a 99% and 85% magnetic retrieval of 5:1 (ZnO@γ-Fe2O3) and 10:1 (ZnO@γ-Fe2O3) catalysts was established. The synthesized catalysts exhibited excellent stability and reproducibility in the photocatalytic performance.

Raman Scattering Characterization of Mo<sub>x</sub>W<sub>1-x</sub>S<sub>2</sub> Layered Mixed Crystals

A systematic study of a series of MoxW1-xS2 layered mixed crystals, with 0 ≥ x ≤ 1, grown by the chemical vapor transport method were carried out by using Raman scattering measurements. The peaks of the two dominant first-order Raman-active modes, A1g and E2g1 , and several second-order bands have been observed in the range of 150-500 cm-1. The peaks corresponding to A1g mode show one-mode type behavior while the peaks of E2g1 mode demonstrate two-mode type behavior for the entire series. The results can be explained on the basis of the atomic displacements for each mode. For A1g mode only sulfur atoms vibrate and this give rise to a one-mode type behavior for the mixed crystals. For E2g1 mode metal atoms also vibrate as well as sulfur atoms, the mass difference of the vibrating Mo and W cations causes the two-mode type behavior of E2g1 mode. In addition, the observation of largest asymmetry and broadening of A1g mode for Mo0.5W0.5S2 has been attributed to random alloy scattering.

Optical properties of ultra-high molecular weight polyethylene (UHMWPE): A material of choice for total joint applications

Abstract In this study optical spectroscopic investigation (from 360 nm to 850 nm) of UHMWPE has been performed using double integrating sphere (DIS) setup. The results revealed that ~9.6% of reference light signal transmitted without interaction i.e. collimated transmitted light was found ~10%. Major portion of reference signal was found to be absorbed, while ~4% of light at each wavelength reflected back from UHMWPE surface. However, de-convolution of absorbance curve having goodness of fit value >98% showed five main absorption peaks at 390 nm, 460 nm, 500 nm, 532 nm and 632 nm, respectively. The absorption peaks at 390 nm and 460 nm belonged to the strong absorption at surface of UHMWPE due to lower penetration depth at these wavelengths, and the peaks at 532 nm and 650 nm might be due to Raman active bands of PE. In addition, maximum collimated transmittance and almost negligible diffuse transmittance of reference signal showed that scattering was total forward directed which revealed the anisotropic nature of UHMWPE.

Speciation of MEA-CO2 Adducts at Equilibrium Using Raman Spectroscopy

Abstract Among a number of initiatives proposed for capturing CO2, the post-combustion technology is attractive as it offers fewer problems to be dealt with and does not require massive reconstruction of the existing power plants, thus reducing the economic penalty. In this paper, we present new vapor liquid equilibrium data for the solubility of CO2 in MEA at 30, 40 and 50 wt% at a temperature of 40 oC. The data are compared with establish data obtained from literature and showed a close agreement. The ability of Raman spectroscopy to quantify the species present during the reaction is explored in this paper. First, calibration plots of carbonate, bicarbonate and carbamate are constructed based on the Raman active bands at 1065 cm-1, 1019 cm-1 and 1034 cm-1, respectively. A detailed analysis of the species present during the reaction of aqueous MEA and CO2 using Raman spectroscopy is discussed in this paper.

Employing microspectroscopy to track charge trapping in operating pentacene OFETs

Ultrathin pentacene films resemble benchmark and model materials for organic field-effect transistors (OFETs). We employ scanning transmission X-ray microspectroscopy (STXM) and confocal Raman microspectroscopy as highly resolving probes to obtain insight into the correlation of morphology and charge transport in pentacene OFETs. By combining the operation-induced intensity increase in Raman-active bands with micromorphology, we are able to visualize charge-induced effects, in particular charge trapping in pentacene OFETs during operation. The high sensitivity and specificity of Raman microscopy allows to distinguish between orientation and charge-induced effects and thus to locate the trapped charges at grain boundaries.

Photocatalytic performances of BiFeO3 particles with the average size in nanometer, submicrometer, and micrometer

Three different synthesis routes were taken to successfully prepare the BiFeO3 particles with the different morphologies and average size in 50, 500nm, and 15μm, respectively. The crystal structure was recognized to be a distorted rhombohedral one with the space group R3c. With the decrease in particle size, obvious decrease in peak intensity and redshift in peak position were observed for the Raman active bands. The narrow band gap was determined from the UV–vis absorption spectra, indicating the semiconducting nature of the BiFeO3. For photodegradation of dyes under visible irradiation in the presence of BiFeO3, the photocatalytic efficiency increased quickly with the decrease in size which may attribute to more surface active catalytic-sites and shorter distances carriers had to migrate to the surface reaction sites.

Quantum Mechanical Interpretation of Intermolecular Vibrational Modes of Crystalline Poly-(R)-3-Hydroxybutyrate Observed in Low-Frequency Raman and Terahertz Spectra

Low-frequency vibrational bands observed in the Raman and terahertz (THz) spectra in the region of 50-150 cm(-1) of crystalline powder poly-(R)-3-hydroxybutyrate (PHB) were assigned based on comparisons of the Raman and THz spectra, polarization directions of THz absorption spectra, and their congruities to quantum mechanically (QM) calculated spectra. This combination, Raman and THz spectroscopies and the QM simulations, has been rarely adopted in spite of its potential of reliable assignments of the vibrational bands. The QM simulation of a spectrum has already been popular in vibrational spectroscopies, but for low-frequency bands of polymers it is still a difficult task due to its large scales of systems and a fact that interactions among polymer chains should be considered in the calculation. In this study, the spectral calculations with the aid of the Cartesian-coordinate tensor transfer (CCT) method were applied successfully to the crystalline PHB, which include the explicit consideration of an intermolecular interaction among helical polymer chains. The agreements between the calculations and the experiments are good in both the Raman and THz spectra in terms of spectral shapes, frequencies, and intensities. A Raman active band at 79 cm(-1) was assigned to the intermolecular vibrational mode of the out-of-plane C═O + CH(3) vibration. A polarization state of the corresponding far-infrared absorption band at ∼82 cm(-1), perpendicular to the helix-elongation direction of PHB, was reproduced only under the explicit correction, which indicates that this polarized band originates from the interaction among the polymer chains. The calculation explored that the polarization direction of this band was along the a axis, which is consistent with the direction in which weak intermolecular hydrogen bonds are suggested between the C═O and CH(3) groups of two parallel polymer chains. The results obtained here have confirmed sensitivity of the low-frequency vibrational bands to the weak hydrogen bonds among the polymer chains.

Microwave-Hydrothermal Synthesis of Transition Metal Tungstates with Nanosized Particles

Microwave-hydrothermal processing was employed to synthesize Mn and Co tungstates under environmentally friendly conditions. X-ray diffraction showed that crystalline, single-phase materials were produced. Incipient crystallized compounds were also obtained in some conditions, as verified by TEM. For these samples, nanostructured regions could be observed inside the amorphous matrix. Sintered solid-solutions of Mn1-xCoxWO4 compounds were produced to investigate the morphological and structural changes in the resulted ceramic. Raman spectroscopy was used to obtain a reliable set of spectra containing all the Raman-active bands predicted by group-theory calculations.

Synthesis, growth and vibrational spectroscopic study of a novel coumarinoylthiazole

An efficient route was developed for the synthesis of novel 3-(2-morpholinyl-4-phenylthiazol-5-oyl)coumarin (MPTC). FT-IR spectrum of MPTC was recorded and analyzed. The crystal structure data are also described. The vibrational wavenumbers were computed theoretically using the Gaussian03 package of programs using HF/6-31G(d) and B3LYP/6-31G(d) levels of theory. The data obtained from vibrational wave number calculations are used to assign vibrational bands observed in the infrared spectra of MPTC. The first hyperpolarizability, infrared absorption band intensities and intensities of raman active bands are reported. The calculated first hyperpolarizability is comparable with the values reported for compounds of similar structure. The structural parameters of MPTC obtained from XRD studies are in agreement with the calculated values. The unit cell parameters of crystals of MPTC are: a=8.6017(10)Å, b=9.9735(5)Å, c=13.3870(13)Å, α=111.123(6)°, β=90.102(9)°, γ=110.246(6)°, and Z=2,1.397Mg/m3.

Calorimetric and vibrational spectroscopic investigations of phase transitions in crystalline [Cr(OS(CH3)2)6](BF4)3

Two phase transitions – one sharp at T1=247.4K and the other very broad at T2∼135K – were observed for [Cr(OS(CH3)2)6](BF4)3 by adiabatic calorimetry. They are of the order–disorder type, and their transition entropies are 28.4 and 8.3JK−1mol−1, respectively. IR absorption and Raman scattering spectroscopy measurements revealed distinct changes in the molecular dynamics of both CH3 groups and BF4− anions at T1 and reduced symmetry of the [Cr(OS(CH3)2)6]3+ complex cations and OS(CH3)2 ligands below T2. The spectral width of an IR and Raman active band associated with the δas(FBF)F2 mode yielded an activation energy (Ea)∼9kJmol−1 for the reorientation of BF4− anions, which is comparable with that obtained for other coordination compounds with BF4− anions.