Strong Raman Lines Research Articles

Structural, morphological, and optical studies of sol–gel spin coated TiO2 thin films

Nanoporous mesostructured Titanium dioxide [TiO2] thin films were deposited on a glass substrate by sol–gel spin coating method using Titanium tetra isopropoxide as a precursor. One set of the prepared samples was annealed at 300 °C for an hour and another set at 400 °C for an hour. The study of structural, morphological, and optical characterizations of these films was carried out using X-ray diffraction (XRD), Raman spectroscopy, FESEM, and UV–vis spectroscopy. The XRD pattern confirms the formation of the anatase phase of TiO2 nanostructured thin films. The strong Raman line at around 144 cm−1 confirms the anatase phase of the synthesized TiO2. FESEM images show plate-like TiO2 particles from micrometer to sub-micrometer size in the grown thin films. The size of the particles was found to be bigger in dimension in the 400 °C annealed TiO2 thin films than in 300 °C annealed TiO2 thin films. The UV–visible optical absorption studies show high optical absorption in TiO2 thin films in the visible region of the electromagnetic spectrum.

Electronic and optical properties of XN-ynes (X = B, Al, Ga): A first-principle study with many-body effects

This study aims to engineer electronic and optical properties of newly designed ‘graphyne with XN at hexagonal ring’ (labeled as XN-ynes, where X = B, Al, Ga). Except BN-yne, all XN-ynes are indirect band gap semiconductors, having larger gap than pristine graphyne. The Raman and IR spectra of XN-yne exhibit quite distinct feature with respect to pristine graphyne and strong Raman and IR line shows regular dependence on group IIIA element, thus may help to detect them during synthesis. The optical band gap calculated by G0W0 and Bethe-Salpeter equation (BSE) approach indicates the possibility of their usage as UV light absorber. The optical band gap is arises from π to π* transition. Not only optical band gap but also the strong absorption peak lies in UV region of electromagnetic spectra that also suggesting their possible use as UV light absorber. This study proposes an important initial step towards the applications of these newly designed XN-ynes.

Revealing Low-Radiative Modes of Nanoresonators with Internal Raman Scattering

Revealing hidden non-radiative (dark) of resonant nanostructures using optical methods such as dark-field spectroscopy often becomes a sophisticated problem due to a weak coupling of these modes with a far-field radiation, whereas methods of dark-modes spectroscopy, e.g. cathodoluminescence or elastic energy losses, are not always convenient in use. Here, we suggest an approach for experimental determining the mode structure of a nanoresonator basing on utilizing intrinsic incoherent Raman scattering. We theoretically predict the efficiency of this approach and realize it experimentally for silicon nanoparticle resonators possessing strong Raman line at 520 cm^-1. With this method, we studied a silicon nanoparticle placed on a gold substrate and reveal the spectral position of a low-radiative magnetic quadrupole mode which is hardly observable with common dark-field optical spectroscopy.

Profiling of CH<sub>4</sub> background mixing ratio in the lower troposphere with Raman lidar: a feasibility experiment

Abstract. We present the results of methane profiling in the lower troposphere using LILAS Raman lidar from the Lille University observatory platform (France). The lidar is based on a frequency-tripled Nd:YAG laser, and nighttime profiling up to 4000 with 100 m height resolution is possible for methane. Agreement between the measured photon-counting rate in the CH4 Raman channel in the free troposphere and numerical simulations for a typical CH4 background mixing ratio (2 ppm) confirms that CH4 Raman scattering is detected. The mixing ratio is calculated from the ratio of methane (395.7 nm) and nitrogen (386.7 nm) Raman backscatters, and within the planetary boundary layer, an increase of the CH4 mixing ratio, up to a factor of 2, is observed. Different possible interfering factors, such as leakage of the elastic signal and aerosol fluorescence, have been taken into consideration. Tests using backscattering from clouds confirmed that the filters in the Raman channel provide sufficient rejection of elastic scattering. The measured methane profiles do not correlate with aerosol backscattering, which corroborates the hypothesis that, in the planetary boundary layer, not aerosol fluorescence but CH4 is observed. However, the fluorescence contribution cannot be completely excluded and, for future measurements, we plan to install an additional control channel close to 393 nm, where no strong Raman lines exist and only fluorescence can be observed.

Vibrational spectroscopy of a crystallographically unsettled uranyl carbonate: Structural impact and model

Room-temperature vibrational and photoluminescence (PL) spectra of a natural, rare hydrated calcium copper uranyl carbonate mineral, voglite (Ca2Cu(UO2)(CO3)4·6H2O) are recorded and discussed in details. Vibrational spectroscopy gives information about the structure of voglite, which is still missing due to its unknown crystallographic features. By comparison with other uranyl carbonates and sulfates, a strong Raman line occurring at 834 cm−1 is assigned to the ν1(UO2)2+ symmetric stretching vibration rather than to the ν2(CO3)2− out-of-plane bending vibration. The ν3(UO2)2+ antisymmetric stretching vibration is tentatively identified at 897 cm−1 from infrared (IR) spectroscopy. Several well resolved bands found at 1074,1092, 1381, 1566 cm−1 in the Raman and 1046, 1114, 1145, 1376, 1426, 1510, 1561 cm−1 in the IR are ascribed to symmetric and antisymmetric stretching motions of the carbonate units. The presence of all these intense vibrational bands points to different CO bond lengths. The infrared water band is well structured, suggesting a few different OH moieties in the crystal. Original micro-PL spectra show a manifold of vibronic features whose energy spacing is close to the frequency of the symmetric OUO stretching vibration and confirms the uranium origin of the most intense Raman band. The study suggests that voglite structure has no inversion centers, a low symmetry, and contains molecular units similar to those of the parent phases, andersonite or liebigite, like uranyl tricarbonate clusters (UTC). The existence of these UTCs in voglite is confirmed by density functional theory calculations. A new assignment of all vibrational modes is proposed.

Defect and Optical Properties of Sb doped and hydrogenated BaSnO3

Polycrystalline undoped and Sb doped BaSnO3 powder samples, BaSn1−xSbxO3 (0 ≤ x ≤ 0.1) have been prepared by hydrogen peroxide assisted method. Hydrogen is incorporated into BaSn1−xSbxO3 to tune the defect and optical properties of the parent oxide. Three localized vibrational modes at 2800–3000 cm−1 in Fourier transform infrared spectra originate from positive and neutral charge states of hydrogen. The observation of strong Raman lines indicate a local structural distortion in a cubic phase of BaSnO3. X-ray photoelectron studies indicate Sn4+ and Sb5+ oxidation states of Sn and Sb in doped samples. The replacement of Sn4+ by Sb5+ enhances the optical band gap from 3.14 ± 0.24 eV in undoped to 3.25 ± 0.20 eV in the 10% Sb-doped sample. Hydrogen impurities act as electron donors and also increase the optical band gap. The overall band gap enhancement has been explained by the Burstein-Moss band filling effect. Two electron paramagnetic resonance signals, corresponding to two kinds of oxygen vacancy centres, are strongly influenced by Sb and hydrogen dopants.

Linear carbon chains inside multi-walled carbon nanotubes: Growth mechanism, thermal stability and electrical properties

Linear carbon chains (LCCs) consisting of sp-hybridized carbon atoms are considered a fascinating 1D system and could be used in the fabrication of the next-generation molecular devices because of its ideal linear atomic nature. A large portion of long LCCs inside multi-walled carbon nanotubes (MWCNTs) were synthesized by atmospheric arc discharge in the presence of boron. Closed-end growth of MWCNTs in the arc process is suggested as a critical condition for the simultaneous growth of LCCs within the inner cores of carbon nanotubes. The strong Raman line around 1850 cm−1 was used to characterize the degree of filling as well as their structural stability under high temperature thermal treatments. We observed a distinctive change in the electrical conductivity of the MWCNT assembly before and after the disappearance of LCCs due to the expected strong coupling interaction between the LCCs and the innermost tube. This work demonstrates for the first time the enhanced effect of confined linear carbon chains on the overall electrical conductivity of MWCNT assemblies.

Silicon-gold-silica lamellar structures for sample substrates that provide an internal standard for Raman microspectroscopy.

Crystalline silicon, widely used in the electronic industry, is also a very popular material for calibrating Raman spectrometry instruments. Silicon chips cut or cleaved from commercially available silicon wafers are low-cost monolithic monocrystalline materials that give a strong Raman line at 521 cm(-1) with almost no background. Such chips have at least one optically flat surface and can be used in place of glass microscope slides as sample substrates that provide an internal calibration standard during Raman measurements. The Raman signal intensity from the silicon can be selectively attenuated by depositing a gold layer on top of the silicon surface with variable thickness such that the far-field silicon Raman signal is comparable with the Raman signal of an investigated material adjacent to this structure. This gold layer provides the additional advantage of increased sensitivity of the spectral signal from the sample due to the reflectivity of the gold surface, which allows forward and backscattered analyte Raman excitation and signal collection. An additional thin encapsulating overlayer of SiO2 provides a protective and biocompatible surface to facilitate Raman microspectroscopic investigation of live cells.

A new μ3-oxo-centered tri-nuclear carboxyl bridged iron (III) complex with thio-methyl groups in the periphery: Structural, spectroscopic and electrochemical studies

A tri-nuclear iron (III) complex [Fe3(μ3-O)(O2CC6H4SCH3)6(Py)3]FeCl4 has been synthesized and characterized by X-ray crystallography, Surface enhanced Raman Scattering (SERS), Fourier Transform Infra Red (FT-IR), Ultraviolet–Visible (UV–Vis) spectroscopy and Thermogravimetric analysis (TGA)/Differential scanning calorimetry (DSC). The functionalized thio-methyl groups around the periphery of the complex 1 may provide binding sites to the surface of some specific materials, such as noble metals. The Ag sols and complex 1-Ag sol had been characterized by SERS and UV–Vis spectroscopy. The complex 1 were also self-assembled on gold electrode by AuS bond, exhibiting an irreversible process at E1/2=0.967V (ΔE=0.525V). Meanwhile the Raman spectra were compared with FT-IR, and the results indicated that the strong Raman lines either correspond to weak Infrared absorptions or are absent in the Infrared spectra.

Application of resonance raman microscopy to in vivo carotenoid.

The high antioxidant activity of astaxanthin has been attracted considerable attention in these days. One of the major antioxidant activities of this carotenoid is anti-photoaging. We have been focusing our attention on this particular issue. The anti-photoaging activity should be functioning in inner skin. In this study we tried to find out the fact that astaxanthin that has been swabbed on the outer surface of the skin has really passed through and reached to the inner skin. For this purpose resonance Raman microscopy was applied to the rat skin sample on which astaxanthin was swabbed on its outer surface. Astaxanthin gives rise to a unique Raman spectrum that is characteristic of its molecular structure. Therefore, we can easily identify the presence or absence of astaxanthin in the area of the rat skin that is subjected to this spectroscopic measurement. We used 532 nm laser light for probing the resonance Raman scattering of astaxanthin. Astaxanthin shows three strong Raman lines at 1508, 1145, and 993 cm(-1). These three lines are ascribable to the C=C stretching, C-C stretching, and C-CH(3) in-plane rocking vibrational modes, respectively. We have constructed confocal Raman microscope that has the spatial resolution of ca. 500 nm. Three-dimensional mapping of the Raman spectrum of astaxanthin has been performed in order to determine its distribution in the rat skin.

Carbonyl-Functionalized Quaterthiophenes: A Study of the Vibrational Raman and Electronic Absorption/Emission Properties Guided by Theoretical Calculations

This work investigates the evolution of the molecular, vibrational, and optical properties within a family of carbonyl-functionalized quaterthiophenes: 5,5'''-diheptanoyl-2,2':5',2'':5'',2'''-quaterthiophene (1), 5,5'''-diperfluorohexylcarbonyl-2,2':5',2'':5'',2'''-quaterthiophene (2), and 2,7-[bis(5-perfluorohexylcarbonylthien-2-yl)]-4H-cyclopenta[2,1-b:3,4-b']-dithiophene-4-one (3). The analysis is performed by Raman and UV/Vis absorption/excitation/fluorescence spectroscopy in combination with density functional calculations. Theoretical calculations show that substitution with carbonyl groups and perfluorohexyl chains induces progressive quinoidization of the π-conjugated backbone in comparison to the carbonyl-free compound 5,5'''-dimethyl-2,2':5',2'':5'',2'''-quaterthiophene (DM-4T) used as reference. Raman spectra are dominated by a strong Raman line which mainly corresponds to a combination of C-C/C=C stretching vibrations spreading over the whole thiophene core. This band undergoes a remarkable downshift as a consequence of the structural changes induced by the electron-withdrawing groups on the π-conjugated backbone. The band splitting on incorporation of a central carbonyl bridge evidences the formation of two structural domains in the molecule. The excitation and fluorescence spectra recorded at low temperature show well-resolved vibronic structures associated with the most intense collective C-C/C=C stretching mode. Optical absorption and fluorescence bands exhibit remarkable bathochromic dispersion on carbonyl functionalization, indicative of extension of π conjugation. TDDFT calculations enable a detailed description of the trends observed in the absorption spectra. Resonance Raman spectra reflect the structural changes predicted for the S(0)→S(1) electronic transition and evidence the cross-conjugated character that the central carbonyl group confers on 3.

Spontaneous Raman scattering spectra of ADP and DADP crystals in different polarization schemes

Spontaneous Raman-scattering spectra of light in ADP and DADP crystals were obtained in four polarization schemes, the widths of some Raman lines were measured. The presence of a strong and sharp Raman line corresponding to the totally symmetric vibration of the phosphate group and a strong diffuse Raman satellite corresponding to the totally symmetric vibration of the ammonium group in the spontaneous scattering spectra of both (ADP and DADP) crystals was observed. According to the theory, such lines are preferable for the stimulated Raman scattering.

Tetrathiafulvalene-Based Materials for Organic Field Effect Transistors. Inspection of Their Semiconductor Properties by Means of Molecular Spectroscopy and Quantum Chemistry

The absorption and emission electronic and vibrational Raman spectra of a series of tetrathiafulvalene compounds have been recorded, assigned with the guide of density functional theory calculations, and interpreted according to their chemical nature of the introduced modifications of the tetrathiafulvalene unit. It turns out that the highest occupied molecular orbital energy can be stabilized while the lowest unoccupied molecular orbital energy is much less affected by substitution of TTF. Importantly, the substitution of tetrathiafulvalene leads to organic materials more resistant to oxidation and operational degradation. The vibrational Raman spectra have been also compared with that of the tetrathiafulvalene unit mainly focusing on the molecular structures. A vibrational splitting in the main lines of the spectra of these derivatives has been recognized and interpreted. The most prominent Raman lines of the spectra combined with the geometrical neutral → cation evolution have been related with the vibrational reorganization energy. These vibrational reorganization energies have been calculated and the trend identified with the behavior of the main Raman lines of the solid-state spectra. Relationships between the strongest Raman lines, the modes with the highest Frank−Condon activities and the vibrational modes with the main contributions to the inner-sphere reorganization energy (i.e., molecular mechanism for relaxing or dissipating energy excess or excitations) have been established. The realization of the connection among these magnitudes supposes a novelty in the field.

First-order Raman spectra ofAB1∕2′B1∕2″O3double perovskites

First-principles computations of Raman intensities were performed for the perovskite-family compound $\mathrm{Ca}{\mathrm{Al}}_{1∕2}{\mathrm{Nb}}_{1∕2}{\mathrm{O}}_{3}$ (CAN). This compound features NaCl-type ordering of Al and Nb superimposed onto the ${b}^{\ensuremath{-}}{b}^{\ensuremath{-}}{c}^{+}$ octahedral tilting. Raman tensor for CAN was computed using the package for first-principles computations ABINIT (URL http://www.abinit.org). Computations performed for both untilted cubic $(\mathit{Fm}\overline{3}m)$ and tilted monoclinic $(P{2}_{1}∕n)$ CAN structures showed that the strongest Raman lines are associated with the ordering of Al and Nb. The computed spectrum agreed qualitatively with the experimental data measured on powder (CAN is available in polycrystalline form only). The effect of cation disorder on the Raman intensities was considered using a phenomenological theory of light scattering in the vicinity of a phase transition. We suggest that, for certain modes, the corresponding Raman intensities depend primarily on the average long-range order whereas, for other modes, the intensities are determined by the fluctuation of the order parameter.

Understanding spectroscopic phonon-assisted defect features in CVD grown 3C-SiC/Si(1 0 0) by modeling and simulation

New phonon-assisted defect features are observed using photoluminescence (PL) and Raman scattering spectroscopy on 3C-SiC/Si(1 0 0) films grown by chemical vapor deposition (CVD) technique. The ultraviolet excitation room-temperature (RT) PL-Raman spectra show a luminescence band near 2.3 eV due to RT recombination over the 3C-SiC indirect band gap. In addition to the strong Raman lines characteristic of Si substrate and 3C-SiC we also observed weaker impurity modes near 620, 743 and 833 cm −1. These frequencies are compared with the results of Green's function simulations of impurity modes with plausible defect structures to best support the observed Raman features as well as modes of some prototypical defect center.

Raman spectroscopy of small-diameter nanotubes

Results based on Raman measurements of small-diameter nanotubes (NTs) are presented and discussed in this paper. The NTs with diameters from 1 nm down to 0.4 nm were produced either as the inner tubes in the double-wall carbon NTs (DWCNTs) or as tubes embedded in the channels of the zeolite crystals. While analysing the Raman spectra attention was paid to the radial breathing mode (RBM), the D line and the G band. For both NT systems the RBM frequency was found to follow the same functional diameter dependence as the tubes with larger diameters. However, in contrast to the latter, the diameters of the thin tubes obtained from density functional theory calculations must be taken into account to explain satisfactorily the observed line positions. The resonance behaviour of the RBM intensities was recorded for the tubes in zeolites. It allows us to ascribe a position of the RBM to a particular NT. This result also demonstrates the breakdown of a simple tight-binding approach to the electronic structure but agrees with predictions from ab initio calculations. The D line of the outer tubes in DWCNTs is dispersive, similar to the single-wall carbon NTs. However, the rate of dispersion is reduced for the inner tubes in DWCNTs. This is attributed to the fact that the inner and outer tubes are probed with the same laser excitation. The linear shift due to the increasing laser energy is compensated by the negative shift due to the NT diameter. The latter is smaller for the inner NTs which leads to a stronger compensation of their dispersive behaviour. This effect is even stronger for the NTs in zeolites. In the extreme case, the strong Raman lines are not dispersive at all. This unexpected behaviour was explained by the detailed ab initio calculation of the phonon structure. The G bands of the inner semiconducting tubes were observed as new features in the Raman spectra of DWCNTs. On the other hand, no lines of metallic inner tubes were found. G bands of semiconducting as well as metallic NTs were detected for the zeolite samples. In either case, Raman lines due to the recently proposed Peierls-like mechanism for the thin metallic tubes were not indentified. This mechanism must therefore cause a significant reduction in Raman intensity.

Raman selection rules in the presence of an electric field gradient

Most of the Raman work (except NSOM) performed near metal surfaces has been concerned with SERS. We do not comment on SERS models here, but note which peaks not normally seen in Raman are expressed. We discuss elsewhere [4] the SERS work on benzene, several cyanides, and C 60 . Here we concentrate on pyrazine, which is a benzene ring with two opposing carbons replaced with N. It has been studied extensively since it is complicated enough to have several vibration modes (with D 2h symmetry), but simple enough that the bulk vibrations are either Raman or IR active, but not both. It has been studied on Ni, Cu, Au, and Ag. [5-7] When shifts of the usual Raman lines between bulk or solution and surface Raman are used as a gauge of substrate interaction, the pyrazine reacts most with Ni, then Au and Cu, and least with Ag. [5] We therefore concentrate on the Ag results. The strong IR line at1484 cm -1 is the strongest new line in the various papers, but with intensity comparable to the normally allowed modes in some studies [6, 7], and much reduced from them in others. [5] Another strong IR line at 1418 cm -1 is often nearly as strong as the 1484 cm -1 line, [5, 7] but absent in other studies [6] and for studies involving the strongly interacting metals. [5] The strong IR – strong new Raman lines analogy for GFR holds, but the irreproducibility is troublesome. Perhaps the orientation of the molecules, which matters in GFR, depends strongly on sample preparation. The intensity of these lines is sensitive to electrochemical potential, [7] and the orientation of pyrazine on Ni does change with concentration, lying flat at low concentrations and on-end at higher concentrations. [5] This could explain why these in-plane (so not GFR affected for flat orientation) vibrations are not completely reproducible. In NSOM, a sharpened optical fiber is coated with aluminum to form an aperture. The probe is positioned near the surface under lateral force feedback. The NSOM is used in illumination mode, with 514 nm Ar ion laser light coupled into the fiber probe. Reflected light is collimated with a 0.50 NA lens, passed through a holographic filter, focused into a Czerny-Turner spectrometer, and finally collected onto a cooled (-45 C) CCD camera. A near field spectra of KTP is shown in Fig. 1. The general shape is typical of the spectra at various distances from the sample. This region of the Raman spectrum contains vibrations primarily from TiO 6 stretching modes in the KTP. The near-field peak shown in green in figure 1 is the strong totally symmetric, A1, vibration mode, which has been observed before in both near- and far-field measurements. [3] The changes observed as the probe approaches the surface are rather small, so we resort to comparative spectra. Several spectra taken far from the surface were averaged and subtracted from single spectra acquired closer to the surface. Two peaks at different energies than the original peaks are observed: the B1 peak (not allowed in the

Observation of Strained PdO in an Aged Pd/Ceria-Zirconia Catalyst

A model automotive-exhaust catalyst, Pd on Zr-rich ceria–zirconia, was characterized by X-ray diffraction, optical and electron microscopies, and micro-Raman spectroscopy following high-temperature aging. A broad bimodal distribution of Pd, introduced amongst the 10-μ m spherical particles of support material during catalyst preparation, was found to persist upon aging, and strained PdO was detected predominantly in those particles containing the higher concentration of Pd. The strain, approximately -1% by volume, was determined from the shift of the strong PdO Raman line at 650 cm-1 and the Grüneisen parameter, which was measured in a separate experiment in a diamond-anvil cell. The origin of the compressive stress that gives rise to this strain is believed to be the same as in the previously known phenomenon of Pd–metal encapsulation, but the Pd particles involved here are apparently not highly constrained within the sintered ceria–zirconia matrix prior to their oxidation.

Structure and the nonlinearity of lithium triborate studied by Raman and infrared reflectivity spectroscopy

Raman and infrared measurements of the LiB3O5 (LBO) crystals were completed. The experimental results shown here are more and stronger Raman lines and infrared absorption peaks, which implies that the external vibrations of the trigonal (BO3)3− and tetrahedral (BO4)5− ions, especially the former, in the six-membered boron–oxygen rings at the low wave number are strong and the internal vibrations of the (BO4)5− ions above 200 cm−1 are stronger than those of the (BO3)3− ions if compared with the Raman spectra of BaB2O4 crystals. These are caused due to the slope and distortions of the B3O7 rings and their BO3 and BO4 units in LBO, which change the structural rigidity of the crystals, intensify the long-range electrostatic force and short-range molecular force, and shorten the ultraviolet absorption edge.

Vibrational assignment of acetylacetone

The infrared and Raman spectra of acetylacetone and its deuterated analogues have been analyzed by the aid of ab initio calculations at post Hartree–Fock level and considering the spectral behavior upon deuteration. By deconvolution of the infrared spectra of acetylacetone and d 6-acetylacetone at 1600 cm −1 region a broad and strong band is found and correlated with the strong Raman lines observed for these compounds in this region. The broadness of this infrared band at room temperature and it's splitting at low temperature is attributed to free rotation of methyl group attached to carbonyl group at room temperature. Furthermore it is found that all ring modes in 1200–1600 cm −1 region more or less are mixed with the OH in plane bending motion.