UV Raman Spectra Research Articles

EPR and UV-Raman study of BPSG thin films: structure and defects

Borophosphosilicate glass (BPSG) films produced by Sub-Atmospheric Pressure Chemical Vapor Deposition (SACVD) with different B and P concentrations have been investigated by ultra-violet (UV) Raman and electron paramagnetic resonance (EPR) spectroscopies. We observe a correlation between the main feature of the UV-Raman spectra in the as deposited films, the line at 1326(2) cm −1 attributed to the stretching vibrations of the PO double bond, and the spin resonance signals attributed to the stable phosphorus–oxygen-hole-center (POHC) created after room temperature X-ray irradiation. The intensity of the PO line as well as the intensity of the POHC EPR signal depend on the B content. The metastable configuration, POHC m , has been also observed by EPR. The B content does not affect significantly the concentration of this paramagnetic defect.

UV Raman spectroscopic study on the synthesis mechanism of zeolite X

The synthesis of zeolite X is characterized by UV Raman spectroscopy, NMR spectroscopy, and X-ray diffraction. UV Raman spectra of the liquid phase of the synthesis system indicate that Al(OH) 4 − species are incorporated into silicate species, and the polymeric silicate species are depolymerized into monomeric silicate species during the early stage of zeolite formation. An intermediate species possessing Raman bands at 307, 503, 858 and 1020 cm −1 is detected during the crystallization in the solid phase transformation. The intermediate species is attributed to the β cage, the secondary building unit of zeolite X. A model for the formation of zeolite X is proposed, which involves four-membered rings connecting to each other via six-membered ring to form β cages, then the β cages interconnect via double six-membered rings to form the framework of zeolite X.

Resonant Raman studies of tetrahedral amorphous carbon films

Resonant Raman scattering has been used to study the tetrahedral amorphous carbon films deposited by the filtered cathodic vacuum arc technique. The excitation wavelengths were 244, 488, 514 and 633 nm, corresponding to photon energies of 5.08, 2.54, 2.41 and 1.96 eV, respectively. In the visible Raman spectra only vibrational modes of sp2-bonded carbon (G and D peaks) are observed, while a wide peak (called the T peak) can be observed at approximately 1100 cm−1 by UV-Raman spectra which is associated with the vibrational mode of sp3-bonded carbon. Both the position and the width of the G peak decrease almost linearly with increasing excitation wavelength, which is interpreted in terms of the selective ππ* resonant Raman scattering of sp2-bonded carbon clusters with various sizes. The G peak position in the UV-Raman spectra, the T peak position and the intensity ratios of ID/IG and IT/IG all exhibit maximum or minimum values at the carbon ion energy of 100 eV. The changes of these spectral parameters are discussed and correlated with the sp3 fraction of carbon atoms in the films.

The active sites in different TS-1 zeolites for propylene epoxidation studied by ultraviolet resonance Raman and ultraviolet visible absorption spectroscopies

The titanium species in four kinds of titanium-containing MFI zeolites have been studied by ultraviolet (UV)-Raman and ultraviolet visible (UV-Vis) absorption spectroscopies and by the epoxidation of propylene with diluted H2O2 solution (30%). UV-Raman spectroscopy is proved to be a suitable means to estimate qualitatively the framework titanium in TS-1 zeolites. Based on the comparison of the relative intensity ratio I1125/I380 of UV-Raman spectra, the TS-1(conv.) sample synthesized hydrothermally by the conventional procedure shows the highest amount of framework titanium. UV-Vis spectroscopy reveals that besides minor anatase, titanium species are mainly tetrahydrally coordinated into the framework for TS-1(conv.) or the Ti-ZSM-5 sample prepared by gas–solid reaction between deboronated B-ZSM-5 and TiCl4 vapor at elevated temperatures. For the TS-1(org.) and TS-1(inorg.) samples synthesized hydrothermally using tetrapropylammonium bromide (TPABr) as template and tetrabutylorthotitanite (TBOT) and TiCl3 as titanium source, respectively, the presence of mononuclear and isolated TiOx species which are proposed to bond to the zeolite extraframework is observed. In addition to the framework titanium species, these isolated TiOx species are assumed to be also active for propylene epoxidation.

A Novel Fluidized Bed Technique for Measuring UV Raman Spectra of Catalysts and Adsorbates

A novel “fluidized bed” (FB) technique for measuring UV Raman spectra of catalysts and adsorbates has been developed to minimize thermal degradation and possible photodecomposition of adsorbates by UV radiation. UV Raman spectra were measured for naphthalene, benzene, and pyridine adsorbed in zeolite H-USY. When measurements were performed on samples in the form of a stationary or spinning disc, the Raman spectra show the presence of “coke,” a typical end product of heating and photochemistry. In contrast, the Raman peaks of the unreacted adsorbates dominate spectra measured using the FB apparatus. An in situ FB reactor was constructed and the UV Raman spectrum of n-heptane in zeolite H-ZSM-5 was measured. These results indicate that the FB technique is a promising method for measuring UV Raman spectra of catalysts and adsorbates.

Disappearance of the LO-Phonon Line in the UV-Raman Spectrum of 6H-SiC

Disappearance of the LO-Phonon Line in the UV-Raman Spectrum of 6H-SiC

Ultraviolet and visible Raman studies of nitrogenated tetrahedral amorphous carbon films

Nitrogenated, tetrahedral amorphous carbon (ta-C) films prepared by the filtered cathodic vacuum arc (FCVA) technique have been studied using ultraviolet (UV, 244 nm) and visible (514 nm) micro-Raman scattering. The nitrogen ions were produced by a RF ion-beam source with a nitrogen flow-rate varying from 0 to 10.0 sccm, which results in a nitrogen content from 0 to 10.8 at.% in the deposited films. In the visible Raman spectra, only vibrational modes of sp 2-bonded carbon (G and D peaks) are observed, while a new wide peak, called the T peak, located at 1090–1320 cm −1, associated with the vibrational mode of sp 3-bonded carbon, appears in the UV-Raman spectra. In the visible Raman spectra, the G-peak width (100–113 cm −1) and the intensity ratio I D/ I G (0.34–0.94) are both sensitive to the structural changes induced by N incorporation. In the UV-Raman spectra, the G-peak position almost linearly decreases from 1665 to 1610 cm −1, and the T-peak position increases tremendously from 1095 to 1314 cm −1 with increasing N content. The G-peak position and width, and the T-peak position, are all sensitive to the bonding structure of the films.

Study on the induction period of methane aromatization over Mo/HZSM-5: partial reduction of Mo species and formation of carbonaceous deposit

The induction period of dehydrogenation and aromatization of methane over Mo/HZSM-5 was studied by combining a pulse reaction method with TPSR, UV laser Raman, and 13C CPMAS NMR techniques. BET and XRD results showed that Mo species were well dispersed on/in the zeolite. TPSR in CH4 stream revealed that Mo species were reduced in at least two different stages before the formation of benzene. TPR results were in agreement with TPSR results. The two stages might be attributed to the reduction of two kinds of Mo6+ species to low valence Mo species. One was polymolybdate MoO3, and the other was crystalline MoO3. UV Raman spectra showed the existence of octahedrally coordinated polymolybdate species. XRD, however, did not detect any crystalline MoO3, possibly because they were too small to be detected with this technique. Pulse reaction results indicated that pre-reduction of the catalyst and formation of carbonaceous deposit could shorten the induction period. It is concluded that the formation of active sites during the induction period via partial reduction of Mo6+ species and formation of carbonaceous deposit on partially reduced Mo species is of significance for methane aromatization over Mo/HZSM-5.

Resonance Raman examination of the two lowest amide ππ* excited states

The UV Raman spectra of N-methylacetamide (NMA) were measured in H2O and D2O between the visible spectral region and the UV region down to 184 nm. The Raman excitation profiles indicate that all of the amide bands are resonance enhanced by the first dipole-allowed π→π* transition at 190 nm. The Raman excitation profile data indicate the presence of destructive interference from the second allowed transition at ca. 165 nm. For example, the amide I and amide I′ bands disappear in the 184 nm UV Raman spectra and the relative intensities of the amide II and III bands change. The first allowed electronic transition at ca. 190 nm occurs to an excited ππ* state where the major geometry change, relative to the ground state, involves a dominating C—N bond elongation, with smaller C—C and N—C bond contractions, and a more modest C=O bond elongation. The C—N ground-state double bond character may decrease to the point where free rotation may occur. This may explain the previously observed monophotonic photoisomerization of trans-NMA to cis-NMA. The second allowed transition at ca. 165 nm occurs to an excited state whose major geometry change involves C=O bond elongation. © 1998 John Wiley & Sons, Ltd.

The status and future of diamond thin film FED

Abstract Field emission displays have emerged as a leading contender of low-power flat panel applications. As one of the promising field emission cathodes (FEC), diamond thin film has some unique advantages over its conventional microtip counterpart because of the superlative physical and chemical properties of diamond and the simplicity of cathode manufacturing. Over the last year, FEPET, Inc., one of the leading organizations in developing FEC, has made tremendous progress in its cathode emission performance, film processing, and understanding of the emission mechanism. Currently, an emission site density (ESD) of 2×10 5 sites per cm 2 and current density of 100 mA/cm 2 have been achieved at an extraction field of about 10 V/μm. We also developed a novel patterning process that allows emission patterning without applying any post-deposition processing to the film to degrade its emission properties. The improvement in film emission properties is found closely related to a diminishing diamond peak and a strongly accentuated graphitic or amorphous carbon shift in the UV-Raman spectra. High-resolution atomic force microscopy (AFM) analysis also showed an association of the emission sites with conductive–insulating–conductive regions of the surface. With the achievable ESD today, diamond film FEC can already find many practical applications such as low- to medium-resolution displays and backlights for liquid crystal display (LCDs). For high-resolution color displays, significant improvement in emission site density is still necessary, and a glass substrate with high-quality surface becomes indispensable. The use of high-temperature glass applied for polysilicon active matrix LCDs (AMLCDs) or a low-temperature diamond thin film deposition process needs, therefore, to be developed.

Uv Studies of Tetrahedral Bonding in Diamondlike Amorphous Carbon

We report ultraviolet (uv) Raman scattering studies of hydrogen-free, diamondlike amorphous carbon thin films with a wide range of tetrahedral bonding. The uv Raman spectra are shown to provide direct evidence for the presence of sp 3 -bonded C atoms in these materials. The experimental results are found to be in excellent agreement with theoretical predictions and contribute to an improved understanding of the mechanism by which the diamondlike fraction develops within the amorphous carbon network. [S0031-9007(97)03420-0] For over a decade, diamondlike amorphous carbon (DLC) has stimulated great interest from both scientific and industrial perspectives. Hydrogen-free DLC has interesting and useful properties [1], such as high hardness, chemical inertness, thermal stability, wide optical gap of ,2 eV, and negative electron affinity. Therefore, this material is important for coating technology and electronic device applications. Typically, it is produced by vacuum arc [2,3] or pulsed laser deposition [4] methods. In contrast to conventional amorphous carbon (a-C) prepared by evaporation or sputtering which consists mostly of threefold or sp 2 -bonded atoms, DLC contains significant fractions (up to 80 at. %) of fourfold or sp 3 -bonded C atoms. In spite of extensive experimental work on DLC, evidence for the presence of sp 3 C atoms is somewhat indirect and measurements of the sp 3 C content tend to be empirical in nature. Although neutron [5] and electron diffractions studies [3] of DLC have been performed, information about the sp 3 C bonding cannot be readily extracted from the measurements. Estimates of the sp 3 C fraction in DLC are usually made by transmission electron energy loss spectroscopy (EELS) which relies on the loss of transitions from the 1s level to the empty p p states [2,6] associated with the presence of sp 2 C atoms. While vibrational spectroscopies in principle can probe changes in bonding more directly, most of the available experimental techniques have not been successful in studies of DLC. Nuclear magnetic resonance (NMR) can detect sp 3 C atoms [7,8] but requires thick samples which are rather difficult to make in the case of DLC due to the high stress and consequent delamination. Inelastic neutron scattering also requires very thick samples. Typically, Raman scattering is a convenient tool for vibrational characterization of amorphous solids, in which case it represents the phonon density of states (PDOS), weighted by a coupling parame

Raman microprobe investigation of sulphur-doped alkali borate glasses

Coloured as well as colourless binary sodium and potassium borate glasses (20–30 mol% Na 20 and 5–35 mol% K 2O) doped with sulphur in various concentrations (0.3–6 wt%) were prepared by melting together the appropriate weights of sodium and potassium carbonates, boric acid and sulphur. Melting was carried out in platinum–2% rhodium crucibles in an electrically heated furnace at 1000°±10°C for 2 h. The glasses were annealed at, depending on alkali content, temperatures in the range 300–350°C for 1 2 h and slowly cooled at the rate of 2°C/min to room temperature to release strain. The Raman microprobe spectra of the glasses prepared were measured in the range of 200 to 1600 cm −1 using the green line of an argon laser (514.5 nm) for Raman spectral excitation. The Raman data obtained in this study were compared with Raman spectral data of known sulphur states stable in sulphur-containing solids and solutions to identify the different states of sulphur formed in the glasses studied. A comparison was also made with published data for similar glass compositions using other spectral techniques. The Raman data obtained were found to support and complement published results of the UV and visible absorption and Raman spectra of sulphur doped glasses of similar compositions.

Ultraviolet Raman spectroscopy characterization of sulfated zirconia catalysts: fresh, deactivated and regenerated

Ultraviolet Raman spectroscopy (UVRS) has been demonstrated to be a powerful new tool for catalysis and surface science studies. UVRS can successfully avoid the surface fluorescence which frequently occurs in normal Raman spectra of many catalysts. Fresh, deactivated and regenerated sulfated-zirconia catalysts have been characterized using this new method. The UV Raman spectrum of the fresh sample is dominated by the tetragonal phase, however, the spectrum of deactivated sulfated zirconia is nearly identical to that of the monoclinic phase of pure zirconia. A regeneration of the deactivated catalyst restores the spectrum back to that of the fresh sample. In addition, a new band at 750 cm−1 associated with the fresh sample attenuates with the deactivation process. This band is tentatively assigned to the surface [ZrO4]4− unit which is assumed to bond to the surface sulfate group. The results indicate that the surface phase of sulfated zirconia is reconstructed from tetragonal to monoclinic phase during the deactivation process while the bulk remains in the tetragonal phase after the deactivation. It is proposed that the surface tetragonal phase is stabilized by sulfate groups, and is associated with the catalytic activity.

MFI-Type Ferrisilicate Catalysts for the Oxidative Dehydrogenation of Alkanes

The influence of extra-framework Al via AlCl3 deposition on the structure of the active Fe sites in Fe/ZSM-35 was investigated by 29Si MAS NMR, UV–visible diffuse reflectance spectroscopy, infrared spectroscopy, UV Raman spectroscopy, and 57Fe Mössbauer spectroscopy combined with catalytic decomposition of N2O. It is found that high-temperature treatment considerably modifies the iron speciation. UV–visible diffuse reflectance spectra and in situ infrared spectra of NO adsorption show that a significant amount of clustered and cationic Fe species is transformed into extra-framework Fe–O–Al mixed oxide species by high-temperature treatment. UV Raman spectra and 57Fe Mössbauer spectra suggest the generation of a binuclear Fe site stabilized by extra-framework Al species with a feature Raman band at 875 cm−1, which is associated with the high activity of N2O decomposition. A possible explanation is that the addition of extra-framework Al species is beneficial for the formation of binuclear active Fe sites bound to extra-framework Al.

UV raman spectroscopy of H2-air flames excited with a narrowband KrF laser

Raman spectra of H2 and H2O in flames excited by a narrowband KrF excimer laser are reported. Observations are made over a porous-plug, flat-flame burner reacting H2 in air, fuel-rich with nitrogen dilution to control the temperature, and with a H2 diffusion flame. Measurements made from UV Raman spectra show good agreement with measurements made by other means, both for gas temperature and relative major species concentrations. Laser-induced fluorescence interferences arising from OH and O2 are observed in emission near the Raman spectra. These interferences do not preclude Raman measurements, however.

Low temperature vibrational and vibronic spectra of adenine single crystals

Both polarized UV absorption and Raman spectra of adeninium sulphate single crystals were measured at 10 K on the same modular UV-VIS spectrometer. Sharp vibronic structure of the lowest-energy absorption band of N1,N7 diprotonated adenine is interpreted in terms of Herzberg-Teller theory. Slight change of adenine molecule geometry localized round the amino group, which is caused by the electronic excitation, and strong vibronic coupling of some vibrational modes with other electronic transitions have been found.

UV Resonance Raman Characterization of Polycyclic Aromatic Hydrocarbons in Coal Liquid Distillates

Ultraviolet resonance Raman spectroscopy has been used to characterize the polycyclic aromatic hydrocarbon composition of a series of distillates of coal-derived liquids. The UV Raman spectra easily monitor changes in the polycyclic aromatic hydrocarbon composition as a function of distillation temperature. Specific species, such as pyrene, can be determined by judicious choice of excitation wavelength.

Formation and reaction of polyenesulfonic acid. I. Reaction of polyethylene films with SO3

AbstractThe surface of polyethylene (PE) film was sulfonated by reaction with gaseous SO3. The structure of the sulfonated PE films was determined on the basis of spectroscopic data such as IR, UV, and resonance Raman spectra. It was confirmed that a PE film and SO3 gave unsaturated sulfonic acids and that, as the reaction proceeded, the elimination of sulfurous acids took place to form sulfonic acids having highly conjugated CC unsaturated bonds.

UV absorption and Raman spectra of the ground states and time-resolved resonance Raman spectra of the lowest excited triplet states of the E and Z isomers of 2,5-dimethyl-1,3,5-hexatriene. Indication of nonequilibration of excited rotamers in the lowest triplet state

UV absorption and Raman spectra of the ground states and time-resolved resonance Raman spectra of the lowest excited triplet states of the E and Z isomers of 2,5-dimethyl-1,3,5-hexatriene. Indication of nonequilibration of excited rotamers in the lowest triplet state