Visible Raman Spectra Research Articles

Influence of temperature on the vibration and electron absorption spectra of all-trans-β-carotene

The effects of temperature on the visible absorption and Raman spectra of all-trans-β-carotene dissolved in dimethyl sulfoxide ranging from 81 to 18°C were determined. The bands of the visible absorption and Raman spectra of all-trans-β-carotene show red and blue shifts, respectively. Changes in the shape of the spectral feature are observed. Raman scattering cross-section increases as temperature decreases. The red shift of the absorption spectrum is attributed to the thermal conformational change-induced decrease in the effective conjugation length in all-trans-β-carotene chains. The molecular structure order increases and the π-electron delocalization extends as temperature decreases. The bandwidth of the electronic energy gap becomes narrow, which causes the slight shift of visible absorption spectrum towards longer wavelengths. An increase in effective conjugation length causes a blue shift of the Raman band. The decreasing difference between CC and CC bond lengths and longer vibrational relaxation time in low temperature makes the line width narrow. The formation of the triplet excited state of all-trans-β-carotene contributes to the asymmetrical growth in the shape of the spectral feature of the (CC bonds) stretching modes. The shoulder observed below 1520cm−1 shows a blue shift. The enhancement of coherent weakly damped CC stretching vibrations increases the Raman scattering cross-section.

Effect of (−)-epigallocatechin gallate on the fibrillation of human serum albumin

Human serum albumin (HSA), the most abundant plasma protein in the human body is known to form fibrils under partial denaturing conditions. Natural polyphenols are known to interact with HSA and some polyphenols have been shown to be potent inhibitors of amyloid fibrillation. (−)-Epigallocatechin gallate (EGCG), the major component of green tea is known to inhibit amyloid fibrillation. In this report, we have investigated the effect of EGCG on native HSA as well as on the fibrillation process of HSA from amide III band analysis of their respective visible Raman spectra. The differential role of the tryptophan (Trp214) residue present in domain II of HSA in the absence and presence of EGCG has been pointed out using fluorescence anisotropy and visible Raman spectroscopy.

Spatial correlation between chemical and topological defects in vitreous silica: UV-resonance Raman study.

A spatial correlation between chemical and topological defects in the tetrahedron network in vitreous silica produced by a fusion process of natural quartz crystals was found by synchrotron-based UV resonance Raman experiments. Furthermore, a quantitative correlation between these defects was obtained by comparing visible Raman and UV absorption spectra. These results indicate that in vitreous silica produced by the fusion process the topological defects disturb the surrounding tetrahedral silica network and induce further disorder regions with sub nanometric sizes.

Effect of pressure on electron-phonon coupling constants of all-trans-beta-carotene

The present paper cited that R Tubino and other people introduced a kind of electron-phonon coupling constants with dimension, which can establish the relation with the Huang-Rhys factor and calculate the electron-phonon coupling constants of every C-C bond vibration mode. There are many reports about the visible absorption and Raman spectra of all-trans-beta-carotene with pressure. But the study about the Raman scattering cross section and the Huang-Rhys factor with pressure have not been reported now. Visible absorption and Raman spectra of all-trans-beta-carotene were measured in carbon disulfide in the pressure range from 0. 04 to 0. 60 GPa. The results indicated that the visible absorption spectra of beta-carotene in nonpolar solvent carbon disulfide are red-shifted with pressure increasing, but the frequency shifts towards higher frequencies in the Raman spectra, the Raman scattering cross section decreases, Huang-Rhys factor increases, and the electron-phonon coupling constants of CC bond vibration modes increase. The mechanism is that all-trans-beta-carotene caused by compression and a decrease in the structurally ordered properties of the molecules leads to narrow energy gap of the pi, shortens effective conjugation length, hinders delocalization of pi-electron, decreases the Raman scattering cross section, and increases the Huang-Rhys factor and the electron-phonon coupling constants.

Distribution of Protein Ramachandran Psi (ψ) Angle Using Non-Resonance Visible Raman Scattering Measurements

Knowing the distribution of Ramachandran angles helps in understanding peptide and protein backbone conformation. Empirical relations are proposed to correlate the spectral profile of the amide III3 band, obtained from ultraviolet resonance Raman measurements (UVRR), with the Ramachandran dihedral psi angle distribution in small peptide and protein molecules, in different environmental conditions (Mikhonin et al. J. Phys. Chem. B 2006, 110, 1928-1943). It has also been used for more complicated structures, like large globular proteins and protein fibrils. In our work here, we use visible Raman spectra and available empirical relations to obtain similar correlations for human serum albumin, hen egg white lysozyme, and human gamma crystallin. We also report the dihedral angle distribution in fibrils and a denatured protein in an ethanol environment using the same spectroscopic technique.

Identification of Fe2(μ-O) and Fe2(μ-O)2 sites in Fe/ZSM-35 by in situ resonance Raman spectroscopy

The structure of the active iron site in Fe/ZSM-35 was investigated by in situ resonance Raman spectroscopy combined with Mössbauer spectroscopy and DFT calculations. In situ UV resonance Raman spectra coupled with 57Fe Mössbauer spectra suggest that the active Fe site for N2O decomposition is an Fe2(μ-O) site, characterized by a Raman band at 875cm−1. In situ visible resonance Raman spectra reveals the formation of an Fe2(μ-O)2 site with a feature Raman band at 730cm−1 upon N2O reacts with the Fe2(μ-O) site. The Raman band intensity at 730cm−1 is decreasing after exposing the Fe2(μ-O)2 site to CH4 due to the formation of methoxide species which mimics the biocatalysis of soluble methane monooxygenase (sMMO).

Temperature effects on structural order of all-trans-β-carotene

The effects of temperature on the visible absorption and Raman spectra of all-trans-β-carotene dissolved in dimethyl sulfoxide at temperatures ranging from 81 ℃ to 18 ℃ were determined. The bands of the visible absorption and Raman spectra of all-trans-β-carotene showed red blue shifts. The bandwidth of the Raman spectra becomes narrow. Raman scattering cross-section increases as the temperature decreases. The red shift of the absorption spectrum is attributed to the thermal conformational change-induced decrease in the effective conjugation length in all-trans-β-carotene chains. The molecular structural order increases and the π-electron delocalization range is extended as the temperature decreases. The red shift in all-trans-β-carotene can be also attributed to the decrease in the liquid density, and the concomitant decrease in the refractive index is shown by the Lorentz-Lorenz relation. The apparent behavior of the temperature-induced band broadening of CC bonds can be associated with the decrease of difference in C-C and C=C bond lengths, and the shorter vibrational relaxation time. The shoulder observed below 1520 cm-1 shows a red shift. The enhancement of coherent weakly-damped CC stretching vibrations may increase the Raman scattering cross-section.

UV Raman and XPS studies of hydrogenous diamond-like carbon films prepared by PECVD

The hydrogenous diamond-like carbon (DLC) films deposited on Si substrates using pulsed glow discharge method are investigated using Raman spectroscopy and X-ray photoelectron spectroscopy method. The UV Raman spectrum for excitation wavelength is 325 nm. UV Raman is particularly useful for hydrogenous DLC, as it gives clear measurements in the D and G peak spectral region even for highly hydrogenated samples, for which the visible Raman spectra are overshadowed by photoluminescence. The sp3 bonding of hydrogenous DLC film can be effectively studied by X-ray photoelectron spectroscopy method, and the data from the X-ray photoelectron spectroscopy method are compared with Raman results. It is found that G peak shows a shift to ward a higher wave under UV excitation. For the G peak, I(D)/I(G), G-FWHM and sp3, there exists a relationship among them.

Double Pulse Electrodeposition of Cu-Ga Precursor Layer for CuGaS2 Solar Energy Thin Film

A novel technique for synthesis of CuGaS2 solar energy thin film is presented. It is associated with double pulse electrodeposition of Cu-Ga precursor layer followed by thermal annealing treatment in sulfur atmosphere. The influence of several flexible parameters including pulse deposition potential and agitation rate on the compositions, crystal structure and morphology of the films were investigated. A relative negative shift of the higher pulse deposition potential results in the increasement of Ga content. A higher agitation rate results in higher Cu/Ga ratio and the emergence of CuS secondary phase after annealing in sulfur atmosphere. The crystal size increases with decreasing the higher pulse deposition potential. Several characterization methods including X-ray diffraction (XRD), scanning electron microscope (SEM), energy diffraction spectrum (EDS), ultraviolet–visible (UV–vis) spectra, impedance spectroscopy, and Raman spectrum are used to characterize the synthesized CuGaS2 polycrystalline thin films. Based on the experimental results, a probable formation mechanism of the CuGaS2 thin films was proposed and briefly discussed.

Effects of annealing temperature on the microstructure and p-type conduction of B-doped nanocrystalline diamond films

Annealing of different temperatures was performed on boron-doped nanocrystalline diamond (BDND) films synthesized by hot filament chemical vapor deposition (HFCVD). Effects of annealing temperature on the microstructural and electrical properties of BDND films were systematically investigated. The Hall-effect results show that smaller resistivity and Hall mobility values as well as higher carrier concentration exist in the 5000 ppm boron-doped nanocrystalline diamond film (NHB) as compared with those in 500 ppm boron-doped nanocrystalline diamond film (NLB). After 1000 ℃ annealing, the Hall mobility of NLB and NHB samples were 53.3 and 39.3 cm2·V-1·s-1, respectively, indicating that annealing increases the Hall mobility and decreases the resistivity of the films. HRTEM, UV, and visible Raman spectroscopic results show that the content of diamond phase in NLB samples is larger than that in NHB samples because higher B-doping concentration results in a greater lattice distortion. After 1000 ℃ annealing, the amount of nano-diamond phase of NLB and NHB samples both increase, indicating that a part of the amorphous carbon transforms into the diamond phase. This provides an opportunity for boron atoms located at the grain boundaries to diffuse into the nano-diamond grains, which increases the concentration of boron in the nano-diamond grains and improves the conductivity of nanocrystalline diamond grains. It is observed that 1000 ℃ annealing treatment is beneficial for lattice perfection of BDND films and reduction of internal stress caused by doping, so that the electrical properties of BDND films are improved. Visible Raman spectra show that the trans-polyacetylene (TPA) peak (1140 cm-1) disappears after 1000 ℃ annealing, which improves the electrical properties of BDND films. It is suggested that the larger the diamond phase content, the better lattice perfection and the less the TPA amount in the annealed BDND samples that prefer to improve the electrical properties of BDND films.

Evolution of thermal disorder in the absorption and Raman spectra of all-trans-β-carotene

The temperature-dependent visible absorption and resonant Raman spectra of all-trans-β-carotene extremely diluted in dimethyl sulfoxide are investigated to clarify the effects of temperature on conjugated polyenes. The visible absorption and Raman spectra are found to blueshift with increasing temperature. The blueshift in polyenes is attributed to the decrease in the liquid density and the concomitant decrease in the refractive index by the Lorentz–Lorenz relation. We demonstrate that visible absorption is reproduced well by simple Franck–Condon analysis using a single Huang–Rhys factor over a temperature range. The analysis reveals features of temperature dependence in terms of important spectral parameters, such as line width, Raman scattering cross section and Huang–Rhys factor.

Near-Infrared (NIR) Raman Spectroscopy of Precambrian Carbonate Stromatolites with Post-Depositional Organic Inclusions

Raman spectroscopy has promising potential for future Mars missions as a non-contact detection technique for characterizing organic material and mineralogy. Such a capability will be useful for selecting samples for detailed analysis on a rover and for selecting samples for return to Earth. Stromatolites are important evidence for the earliest life on Earth and are promising targets for Mars investigations. Although constructed by microorganisms, stromatolites are organo-sedimentary structures that can be large enough to be discovered and investigated by a Mars rover. In this paper, we report the Raman spectroscopic investigations of the carbonate mineralogy and organic layering in a Precambrian (~1.5 Gyr old) stromatolite from the Crystal Spring Formation of Southern California. Ultraviolet (UV: 266 nm), visible (514 nm, 633 nm), and near-infrared (NIR: 785 nm, 1064 nm) Raman spectra are presented. We conclude that 1064 nm excitation is the optimal excitation wavelength for avoiding intrinsic fluorescence and detecting organic carbon within the carbonate matrix. Our results confirm that NIR Raman spectroscopy has important applications for future Mars missions.

Morphology Dependence of Catalytic Properties of Ni/CeO2 Nanostructures for Carbon Dioxide Reforming of Methane

The comparative catalytic activity and coke resistance are examined in carbon dioxide reforming of methane over Ni/CeO2 nanorods (NR) and nanopolyhedra (NP). The Ni/CeO2–NR catalysts display more excellent catalytic activity and higher coke resistance compared with the Ni/CeO2–NP. The high resolution transmission electron microscope reveals that the predominantly exposed planes are the unusually reactive {110} and {100} planes on the CeO2–NR rather than the stable {111} one on the CeO2–NP. The prepared samples were also characterized by X-ray diffraction, transmission electron microscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, UV and visible Raman spectra, and oxygen temperature-programmed oxidation. The {110} and {100} planes show great superiority for the anchoring of Ni nanoparticles, which results in the existence of strong metal–support interaction effect (SMSI). The SMSI effect can be helpful to prevent sintering of Ni particles, which benefits to reduce the deactivation of catalytic activity. Besides, the oxygen vacancies and the mobility of lattice oxygen also show the morphology dependence. They can participate into the catalytic reaction and be beneficial to the activation of carbon deposition. In conclusion, the excellent catalytic activity and coke resistance of the Ni/CeO2–NR should be attributed to the SMSI effect and abundant oxygen vacancies.

Two-step photoionization of trans-stilbene in acetonitrile via an ion-pair precursor studied with picosecond time-resolved absorption and Raman spectroscopies

Picosecond time-resolved visible absorption and Raman spectra of trans-stilbene in acetonitrile have been measured. A new transient absorption band is observed at 440nm, whose decay time constant coincides with that of the rise of the radical cation. In addition to the known Raman bands of the radical cation, a new Raman feature showing a fast decay is found at 1599cm−1. We assign the 440nm absorption band and the 1599cm−1 Raman band to a precursor of the radical cation. The precursor may well be an ion pair that holds an ejected electron still around the cation.

The effect of nitrogen ion bombarding energy on the bonding structure of nitrogenated tetrahedral amorphous carbon film

The tetrahedral amorphous carbon (ta-C) films with more than 80% sp3 in fraction are deposited by the filtered cathode vacuum arc technique. Then the energetic nitrogen (N) ions are used to bombard the ta-C films to fabricate nitrogenated tetrahedral amorphous carbon (ta-C:N) films. The composition and the structure of the films are analyzed by visible Raman spectrum and X-ray photoelectron spectroscopy. The result shows that the bombardment of energetic nitrogen ions can form CN bonds, convert CC bonds into C＝C bonds, and increase the size of sp2 cluster. The CN bonds are composed of C＝N bonds and CN bonds. The content of C＝N bonds increases with the N ion bombardment energy increasing, but the content of CN bonds is inversely proportional to the increase of nitrogen ion energy. In addition, CN bonds do not exist in the films.

Effects of annealing time on the microstructural and electrochemical properties of B-doped nanocrystalline diamond films

The effects of annealing time under 1000 ℃ on the microstructural and the electrochemical properties of boron-doped nanocrystalline diamond (BDND) films are investigated by HRTEM, UV and visible Raman spectroscopy, and cyclic voltammetry measurements. The results show that the size of nano-diamond grain in the film decreases with annealing time increasing. When the annealing time is 0.5 h, the grain size decreases from about 15 nm in the unannealed sample to about 8 nm and the content of diamond phase increases. When the annealing time increases to 2.0 h, the diamond grain size decreases to 2-3 nm, and the content of diamond phase decreases with the grain boundary increasing. In the case of annealing time of 2.5 h, the grain size of nano-diamond and the content of diamond phase increase slightly. The variations of nano-diamond grain size and the content of diamond phase indicate that the transformation between the diamond phase and the amorphous carbon occurs under the annealing with different times. The visible Raman spectra show that the G-peak position and the ID/IG value exhibit similar variations with annealing time increasing, revealing that the ordering of the amorphous graphite phase is improved when sp2 carbon cluster increases in number or size. The reactions on the electrode surface are quasi-reversible when the annealing times are 0.5, 1.0, 1.5 and 2.0 h. On the contrary, the reactions are irreversible when the sample is unannealed or annealed for 2.5 h. It is observed that the annealing treatment is beneficial to the improvement of the electrode mass transfer efficiency of BDND film. When the annealing time is 0.5 h, the electrode mass transfer efficiency as well as the ability of catalytic oxidation of BDND film is best. The results suggest that the smaller size of nano-diamond grain, the higher content of diamond phase and the uniform distribution of the nanocrystalline diamond grains are conducible to the improvement of the reaction reversibility on the electrode surface and the ability of catalytic oxidation of BDND films.

Mega-electron-volt proton irradiation on supported and suspended graphene: A Raman spectroscopic layer dependent study

Graphene samples with 1, 2, and 4 layers and 1 + 1 folded bi-layers and graphite have been irradiated with 2 MeV protons at fluences ranging from 1 × 1015 to 6 × 1018 ions/cm2. The samples were characterized using visible and UV Raman spectroscopy and Raman microscopy. The ion-induced defects were found to decrease with increasing number of layers. Graphene samples suspended over etched holes in SiO2 have been fabricated and used to investigate the influence of the substrate SiO2 for defect creation in graphene. While Raman vibrational modes at 1460 cm−1 and 1555 cm−1 have been observed in the visible Raman spectra of substantially damaged graphene samples, these modes were absent in the irradiated-suspended monolayer graphene.

UV and visible Raman scattering of ultraheavily Ti implanted Si layers for intermediate band formation

We assess the degree of crystallinity by means of UV and visible Raman scattering measurements of Ti implanted Si layers with very high doses (1015–5 × 1016 cm−2) subsequently annealed by nanosecond pulsed laser melting (PLM). We obtain ultraheavily impurified Si layers with Ti concentrations six orders of magnitude above the solid solubility limit in a layer several tens of nanometers thick. The PLM annealing processes are needed to recover the crystal quality and to keep the high Ti concentration required to form an intermediate band (IB). The UV Raman analysis permits us to evaluate the lattice crystallinity of the different implanted doses probing only the implanted region and points out Ti interstitial location in the host lattice in agreement with theoretical predictions for IB formation. By contrast, visible Raman spectra are only sensitive to the presence of a fully amorphized implanted layer as in the rest of the crystalline layers the probing depth far exceeds the implanted layer thickness and the signal is dominated by the undamaged Si.

Raman Spectroscopy Using a Spatial Heterodyne Spectrometer: Proof of Concept

The use of a spatial heterodyne interferometer-based spectrometer (SHS) for Raman spectroscopy is described. The motivation for this work is to develop a small, rugged, high-resolution ultraviolet (UV) Raman spectrometer that is compatible with pulsed laser sources and that is suitable for planetary space missions. UV Raman is a particular technical challenge for space applications because dispersive (grating) approaches require large spectrographs and very narrow slits to achieve the spectral resolution required to maximize the potential of Raman spectroscopy. The heterodyne approach of the SHS has only a weak coupling of resolution and throughput, so a high-resolution UV SHS can both be small and employ a wide slit to maximize throughput. The SHS measures all optical path differences in its interferogram simultaneously with a detector array, so the technique is compatible with gated detection using pulsed lasers, important to reject ambient background and mitigate fluorescence (already low in the UV) that might be encountered on a planetary surface where samples are uncontrolled. The SHS has no moving parts, and as the spectrum is heterodyned around the laser wavelength, it is particularly suitable for Raman measurements. In this preliminary report we demonstrate the ability to measure visible wavelength Raman spectra of liquid and solid materials using an SHS Raman spectrometer and a visible laser. Spectral resolution and bandpass are also discussed. Separation of anti-Stokes and Stokes Raman bands is demonstrated using two different approaches. Finally spectral bandpass doubling is demonstrated by forming an interference pattern in both directions on the ICCD detector followed by analysis using a two-dimensional Fourier transform.

Effect of hydrogen flow on the properties of hydrogenated amorphous carbon films fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition

The hydrogenated amorphous carbon films (a-C:H, so-called diamond-like carbon, DLC) have exceptional physical and mechanical properties and have wide applications. In the present study, amorphous hydrogenated carbon films (a-C:H) have been deposited on a Si (100) substrate at different hydrogen flow using electron cyclotron resonance chemical vapor deposition (ECR-CVD). The flow of hydrogen changed from 10 sccm to 40 sccm and the flow of acetylene was fixed at 10 sccm. The microstructure and properties of the a-C:H were measured using visible Raman spectra, Fourier transform infrared (FTIR) spectroscopy, UV–VIS spectrometer,surface profilometer and nano-indentation. The results showed that the sp 3 content and sp 3–CH 2 structure in the amorphous hydrogenated carbon films increased with the hydrogen flow. The deposition rate decreased with the hydrogen flow. The residual stress and the nano-hardness of the amorphous hydrogenated carbon films increased with the hydrogen flow. Consequently, the a-C:H film become more diamond-like with the increase of hydrogen flow.