Showing papers on "Raman spectroscopy published in 1988"

The Raman spectra of Co3O4

Abstract: The Raman spectra of single-crystal Co3O4 have been measured at 312 K. Five Raman-active modes were found and identified at 194, 482, 522, 618 and 691 cm-1.

Raman scattering characterization of carbon bonding in diamond and diamondlike thin films

Abstract: The atomic bonding configurations of carbon bonding in diamond and diamondlike thin films are explored using Raman scattering. The general aspects of Raman scattering from composites are presented. Effects are discussed due to crystalline or amorphous structures, large versus microcrystalline domains, and strong optical absorption and transparent regions. The Raman scattering from diamondlike films shows several features which are attributed to microcrystalline graphitelike structures which all originate from the same region in the sample. In contrast, the spectra of diamond films show features attributed to different components of a composite film. Components identified are crystalline diamond, and disordered and microcrystalline graphitic structures. The presence of precursor microcrystalline or amorphous diamond structures is also suggested.

The formation of hydrogen passivated silicon single‐crystal surfaces using ultraviolet cleaning and HF etching

Abstract: We have tried to develop a new procedure to prepare the clean surface of a silicon single crystal. We successfully prepared the contamination free bare silicon surface with ultraviolet cleaning followed by HF dipping with low concentration HF obtained by dilution by organic free ultrapure water, at room temperature under the atmospheric condition. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet photoelectron spectroscopy measurements proved thus prepared surface has a hydrogen monoatomic layer terminating the dangling bonds of silicon. The hydrogen termination was found to have remarkable passivation effect against surface oxidation reaction. A silicon thin‐film epitaxially grown on the prepared surface was confirmed to have perfect crystal structure and high‐purity level by scanning electron microscopy, reflection high‐energy electron diffraction, Raman spectroscopy and secondary ion mass spectroscopy.

Experimental determination of the nanocrystalline volume fraction in silicon thin films from Raman spectroscopy

Abstract: The effect of crystallite sizes L smaller than 100 nm on the integrated Raman cross section Σc of the transverse optical (TO) mode of fcc silicon was studied experimentally in fully nanocrystallized thin films. The Σc/Σa (amorphous) ratio of this mode is shown to be 1 up to L=30 A, and to decay exponentially down to 0.1 at larger L. A systematic procedure taking into account both this effect and the experimental optical absorption coefficient αexp at the excitation wavelength is then proposed for the determination of the crystalline volume fraction in mixed phase (amorphous/nanocrystalline) silicon systems by Raman measurements.

High rate synthesis of diamond by dc plasma jet chemical vapor deposition

Abstract: This letter describes the first successful attempt at synthesizing diamond by chemical vapor deposition with the use of a dc plasma jet. A plasma jet, formed by the dc arc discharge of CH4 diluted with H2, was sprayed onto a water‐cooled substrate. The growth rate of the diamond film was 80 μm/h. The crystallinity measures well in terms of x‐ray diffraction and Raman spectroscopy. The quenching effect of the thermal plasma is discussed in relation to the high growth rate obtained.

Raman spectra of diamondlike amorphous carbon films

Abstract: Raman spectra of diamondlike amorphous carbon (a‐C) films prepared under atmosphere with various hydrogen gas content have been measured as a function of excitation wavelength. The Raman spectral profiles vary with excitation wavelength depending on electronic absorption spectra associated with π‐π* electronic transitions. Dependence of Raman spectra on excitation wavelength is interpreted in terms of π‐π* resonant Raman scattering from aromatic rings with various sizes rather than polyene chains. The relative intensity of a 1400 cm−1 band against a 1530 cm−1 band is found to decrease with an increase of sp3 content in a‐C films. It is shown that the relative intensity can be used as a parameter for sp3 content.

Characterization of individual tryptophan side chains in proteins using Raman spectroscopy and hydrogen-deuterium exchange kinetics

Abstract: Two Raman bands at 880 and 1350 cm/sup -1/ of tryptophan (Trp) side chains have been found useful in structural studies of the side chains in proteins. The frequency of the 880-cm/sup -1/ band reflects the strength of H bonding at the N/sub 1/H site of the indole ring: the lower the frequency is, the stronger the H bonding is. The intensity of the 1360-cm/sup -1/ band, on the other hand, is a marker of the hydrophobicity of the environment of the indole ring: particularly strong in hydrophobic environments. It is also demonstrated that a combination of stepwise deuteriation of the tryptophan side chains and difference spectrum techniques is useful to observe these marker bands due to each side chain separately. The states of six tryptophans in lysozyme revealed by the Raman spectroscopic method in solution are compared with those by X-ray diffraction in crystal. The Raman data on the outer four Trp's are consistent with the X-ray structure, whereas significant differences between solution and crystal are suggested for the strength of H bonding of the most and second most buried Trp's. Characterization of four Trp's in ..cap alpha..-lactalbumin shows that the two outer Trp's are moderately H bonded tomore » solvent water and closely surrounded by aliphatic side chains while the inner two are not H bonded nor closely surrounded by aliphatic side chains.« less

NMR confirmation of strained “defects” in amorphous silica

Abstract: Solid state 29 Si magic angle sample spinning nuclear magnetic resonance spectroscopy and Raman spectroscopy were used to investigate the local silicon environment and siloxane ring vibrations in amorphous silica gels. Our results unambiguously relate the 608 cm −1 Raman “defect” in a-SiO 2 with reduced SiOSi bond angles indicative of strained 3-membered rings of silicate tetrahedra.

Raman spectroscopy of low-dimensional semiconductors

Abstract: Raman spectroscopy is widely used to study the vibrational and structural properties of single crystals. More recently, in the fields of chemistry, physics, and engineering, interest in the properties of small objects has arisen. Small objects include microcrystalline materials, artificially layered semiconductor structures, and colloidal suspensions. The reason for this recent interest is that these objects often display unique electronic properties which may find applications in devices. Since Raman spectroscopy is a convenient nondestructive tool, it is not surprising that it has been used to characterize such objects. In this review, we consider almost exclusively results obtained with semiconductors.

Combustion diagnostics: Planar imaging techniques

Abstract: New measurement techniques based on planar (2-d) imaging of scattered light provide a powerful complement to single-point laser-based diagnostics, with significant potential to impact combustion research. Though still in an early stage of development, these imaging methods offer prospects for non-invasive, spatially and temporally resolved measurements of species concentrations and moler fractions, temperature, density, velocity, and pressure. Imaging processes encompassed in this review include laser-induced fluorescence and Raman, Mie and Rayleigh scattering. Extensions of these 2-d techniques to new flowfield variables and species, and to 3-d imaging by rapid scanning of the illumination plane, are already in progress.

Diamond crystal growth by plasma chemical vapor deposition

Abstract: We have grown diamond crystals and polycrystalline diamond films from CH4/H2/O2 gas feeds in a simple, high‐power density, 2450‐MHz discharge tube reactor. Single‐crystal growth rates over 20 μm/h have been achieved. The material has been analyzed using Raman spectroscopy, Auger spectroscopy, and x‐ray diffraction. Control of nucleation is a major problem for growing sound films, and the high temperatures currently required for growth will limit applications. Oxygen additions were necessary to deposit diamonds over the range of feed composition we studied.

Spectroscopy of surfaces

Abstract: Structure and Orientation in Thin Films: Raman Studies with Integrated Optical Techniques Surface Rules for Surface-Enhanced Raman Spectroscopy The Application of Surface- Enhanced Raman Scattering to Biochemical Systems Static SIMS for Surface Analysis Inelastic Electron Tunnelling Spectroscopy in Chemistry Electron-Excited Surface Spectroscopies Electron Energy Loss Spectroscopy Infrared Reflection-Absorption Spectroscopy of Adsorbed Molecules.

UV resonance Raman studies of molecular structure and dynamics: applications in physical and biophysical chemistry

Abstract: A fundamental understanding of molecular structure and dynamics requires a close coupling between theory and experiment. One ultimate objective is to utilize the understanding of molecular structure and dynamics to predict both molecular properties such as chemical reactivity and bulk properties such as phase behavior and material strengths. Often the major driving force for progress in science is the development of new experimental techniques capable of incisive glimpses into simple phenomena in complex systems. This is especially important for studies of large polyatomic molecules, and is crucial for the macromolecules studied in biology and biochemistry that control life processes. This review outlines the recent progress in the development of UV resonance Raman spectroscopy (UVRR) as a new technique for the study of molecular structure and dynamics for both small molecules and larger molecules such as polypeptides and proteins. This recent work follows the pioneering UV Raman nucleic acid studies in 1975, which used frequency doubled Ar laser excitation at 257 nm (1-4), and Ziegler & Albrecht’s pioneering nitrogen-dye laser preresonance Raman benzene derivative studies, which set the stage for true resonance Raman investigations of benzene derivatives and other aromatics (5-8). This work was followed

Characterization of Redox States of Nickel Hydroxide Film Electrodes by In Situ Surface Raman Spectroscopy

Abstract: Thin films of nickel hydroxide deposited on gold electrodes have been characterized in detail by in situ surface Raman spectroscopy in conjunction with electrochemical techniques. Raman spectra were obtained for film thicknesses varying from less than one equivalent monolayer to several hundred monolayers, as determined from the faradaic charge for the cyclic voltammetric oxidation of . For the thinnest films, Raman bands at 455 cm−1 and at 480 and 560 cm−1were obtained for the reduced and oxidized films, respectively, using 647.1 nm excitation at roughened gold. These signals, identified with Ni‐OH and Ni‐O vibrations from deuterium isotope data, were diagnosed as arising from surface‐enhanced Raman scattering (SERS) in view of their absence for the reduced film when using smooth gold surfaces and/or green/blue laser excitation. Raman spectra were obtained using the latter conditions for thicker oxidized films, which were consistent with resonance Raman scattering (RRS). Analysis of the dependence of the band intensities as a function of film thickness under conditions where SERS or RRS predominates enables the relative contributions of these mechanisms as well as the influence of film absorbance to be assessed quantitatively. Raman spectra were also obtained in air and after "film aging" by potential cycling or heating. The spectral changes following the latter treatments support the evolution of a less hydrogen‐bound film structure, i.e., the transformation of . By combining cyclic voltammetry with analysis of the dissolved film using atomic absorption spectroscopy, the effective oxidation state of nickel in the oxidized films is determined to be . On the basis of the spectroscopic and electrochemical measurements, the most likely structure for the oxidized film is a hydrated form of , where M is the supporting electrolyte cation.

Is bound carbonyl linear or bent in heme proteins? Evidence from resonance Raman and infrared spectroscopic data.

Abstract: The vibrational data on heme-CO complexes are analyzed with a view toward elucidating the structural evidence for distorted FeCO units in heme proteins. The effects of FeCO distortion on the vibrational frequencies are attributable to back-bonding changes, as evidenced by the correlation of vF& with vCo. Steric restraint of perpendicular binding increases Fe CO back-donation slightly. This is opposite to the direction expected if the FeCO unit is bent but is consistent with the expected effect of two other distortion coordinates, FeCO tilting and porphyrin buckling. Larger effects on back-bonding are attributable to polar interactions of distal residues with the bound CO, especially H bonding. Substantial FeCO bending is inconsistent with the relatively small frequency separation between vFeC and dFeCO observed in all adducts so far examined; this separation is calculated to increase strongly with the bending angle due to mixing of the modes. For a given displacement of the 0 atom from the heme normal, the energy required for the three distortion coordinates is calculated to increase in the order tilting < buckling < bending. The energy is minimized, as are the individual angular displacements, if all three contribute to the actual molecular distortion, and the small net change may result from the opposing effects of bending and of tilting and buckling in vFcc. This concerted model of FeCO distortion is not inconsistent with the available X-ray crystal structure data. It is inconsistent with EXAFS analysis of MbCO at 4 K, which has yielded a small value, 127 f 4O, for the FeCO angle from the attenuation of second-shell scattering relative to a protein-free model. This attenuation might be due instead to other changes in second-shell scattering, e.g. due to porphyrin buckling. functional role in lowering the C O affinit;, thereby raising ;he threshold for CO poisoning. Whether the CO affinity is actually (2) (a) Peng, S. M.; Ibers, J. A. J . Am. Chem. SOC. 1976, 98, 8032. (b) Scheidt. W. R.; Haller. K. J.: Fons. M.: Fashiko. T.: Reed. C. A. Biochemistrv (1) (a) Kuriyan, J.; Wiltz, S.; Karplus, M.; Petsko, G. J . Mol. Bid . 1986, 192, 133-154. (b) Hanson, J. C.; Schoenborn, B. P. J . Mol. Biol. 1981, 153, 117. (c) Baldwin, J. M.; Chothia, C. J . Mol. Biol. 1979, 129, 175. (d) Baldwin, J. M. J . Mol. Biol. 1980, 136, 103. (e) Steigeman, W.; Weber, E. J . Mol. B i d . 1979, 127, 309. (0 Tucker, P. W.; Philipps, S. E. V.; Perutz. M. F.; Houtchens, R. A.; Caughey, W. S. Proc. Natl. Aidd. Sci. U S . A . 1978, 75, 1076. (g) Heidner, E. J.; Ladner, R. C.; Perutz, M. F. J. Mol. Bid . 1976, 104, 707. (h) Norvell, J. C.; Nunes, A. C.; Schoenborn, B. P. Science (Washington, D.C.) 1975, 190, 568. ( i ) Padlan, E. A.; Love, W. E. J . Biol. Chem. 1974,249,4067. (j) Huber, R.; Epp, 0.; Formanek, H. J . Mol. Biol. 1970, 52, 349. 1981, 20, 3653. (c) Caron, C.; Mitschler, A,; Riviere, G.; Ricard, L:; Schappacher, M.; Weiss, R. J . Am. Chem. SOC. 1979, 101, 7401. (3) (a) Collman, J. P.; Brauman, J. I.; Halbert, T. R.; Suslick, K. S. Proc. Natl. Acad. Sci. U.S.A. 1976, 73, 3333. (b) Collman, J. P.; Brauman, J. I.; Everson, B. L.; Sessler, J. L.; Morris, R. M.; Gibson, Q. H. J. Am. Chem. SOC. 1983, 105, 3052. 0002-7863/88/1510-6024$01.50/0

Resonant impulsive-stimulated Raman scattering on malachite green.

Abstract: We have studied in the femtosecond regime the transient dynamics of dichroism (anisotropic absorption), birefringence, and frequency shift induced by an intense femtosecond pump beam in the dye malachite green in solution. Vibrational quantum beats were observed superimposed on the saturated absorption and dispersion signals and quantitatively explained in terms of impulsive-stimulated Raman scattering close to an electronic resonance. The selectivity for observation of the vibrations in the two electronic states is described for the different experimental schemes. We discuss the access to vibrational and electronic dynamics in both ground and excited electronic states and compare the possibilities to those of previous techniques.

A surface enhanced hyper‐Raman scattering study of pyridine adsorbed onto silver: Experiment and theory

Abstract: This paper presents a combined experimental and theoretical study of the hyper‐Raman spectrum of pyridine adsorbed onto roughened silver electrodes. The surface enhanced hyper‐Raman spectra (SEHRS) were measured using a focused cw mode‐locked Nd:YAG laser with a peak power density of approximately 107 W/cm2 . Dominant bands in the pyridine spectra are the same (totally symmetric) bands as have been seen in the corresponding Raman (SERS) spectrum, although the relative intensities are different. To interpret these spectra, we present a semiempirical molecular orbital method for determining excitation energies, polarizability derivatives, and hyperpolarizability derivatives that is based on the π‐electron Pariser–Parr–Pople (PPP) method. An empirical molecular force field is used to derive vibrational information, and the accuracy of the spectra is assessed by comparison with normal Raman spectra for liquid pyridine and with SERS spectra. The resulting SEHRS spectra are in good agreement with the measured s...

Raman scattering studies of chemical-vapor-deposited cubic SiC films of (100) Si

Abstract: Raman scattering studies for a series of CVD-grown cubic SiC single-crystal films with film thickness from 600 A to 17 microns are discussed. The results suggest that the crystalline orientations of the Si substrate and the 3C-SiC film are the same. It is found that the Si 522/cm phonon from a Si wafer is enhanced in intensity by a factor of 2-3 due to a CVD overlayer of cubic SiC, and that the 3C-SiC longitudinal optical phonon at the Gamma point from SiC/Si samples is enhanced by a factor of two or three following the removal of the Si substrate. The variation of the Raman spectrum with incident power is investigated, and a method for determining the Raman cross section for 3 C-SiC is proposed.

Vibrational spectra and normal-coordinate analysis of tris(bipyridine)ruthenium(II)

Abstract: The infrared and resonance Raman spectra of the tris-bipyridine ruthenium(II) complex and several of its deuterated analogues are reported; specifically, those of the complexes of 3,3'-dideutero-2,2'-bipyridine, 6,6'-dideutero-2,2'-bipyridine and perdeutero-2,2'-bipyridine. Multiple excitation lines are employed to obtain the resonance Raman spectra in order to facilitate observation of all A/sub 1/ fundamental vibrations associated with the ligand framework. Normal coordinate calculations are carried out employing a systematic procedure based on a modified valence force field which is comparable to those used previously for aromatic molecules. The resultant (30 force constant) field reproduces observed frequencies with an average error of approx.2%. 28 refs., 3 figs., 3 tabs.

Coherent molecular vibrational motion observed in the time domain through impulsive stimulated Raman scattering

Abstract: Femtosecond time-resolved observations of coherent molecular vibrations are carried out through impulse-stimulated Raman scattering (ISRS). Individual cycles of vibrational oscillation, as well as vibrational dephasing, are time resolved. ISRS therefore provides a means through which time-resolved spectroscopy of vibrationally distorted molecules can be carried out. Several experimental configurations involving either crossed excitation pulses or a single excitation pulse are discussed theoretically and demonstrated experimentally. >

Fission of optical solitons induced by stimulated Raman effect.

Abstract: Fission of optical solitons in a glass fiber induced by the stimulated Raman effect is demonstrated by a theory, simulations, and experiments. The solitons born by fission retain the amplitudes predicted by inverse-scattering calculations. For n = 2 solitons, fission occurs within a distance of 15 km for an initial pulse width of 10 psec.

High pressure solid phases of benzene. I. Raman and x‐ray studies of C6H6 at 294 K up to 25 GPa

Abstract: Crystalline benzene has been investigated at room temperature as a function of pressure up to 25 GPa in diamond anvil cells by Raman scattering and powder x‐ray diffraction techniques. The concomitant spectroscopic and crystallographic results show the existence of numerous pressure‐induced phases. Changes in the profiles of the Raman spectra and in the x‐ray diffraction patterns, as well as changes in the variations of the Raman frequencies and the cell parameters with pressure indicate two first‐order phase transitions at 1.4±0.1 and 4±1 GPa and a second‐order one at 11±1 GPa. At 24 GPa the x‐ray diffraction pattern seems to indicate the existence of a new phase. Two monoclinic structures are proposed for the phases above 1.5 GPa, in addition to the already known one. From these data, molar volume has been determined as a function of pressure and the Gruneisen parameters have been inferred in the different phases. Their pressure dependences are analyzed in the light of theoretical predictions. Arguments are given for a phase transformation at normal pressure and below 140 K or at room temperature below 1 GPa. A schematic P–T phase diagram is suggested and a controversy on the nature of the triple points located on the melting curve is clarified.