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Showing papers on "Raman spectroscopy published in 1991"


Book
22 Oct 1991
TL;DR: The -NH2, -NHR, and -NR2 groups as discussed by the authors are the most commonly used groups for double bonds containing Nitrogen Atoms, and the -C=N and -N=C groups.
Abstract: Alkanes. Halocompounds. Alcohols and Phenols. Ethers and Peroxides. Alkenes. Acetylenes. The -C=N and -N=C Groups. Compounds Containing the Carbonyl Group. Compounds Containing -NH2, -NHR, and -NR2 Groups. The Nitro Group. Double Bonds Containing Nitrogen Atoms. Cumulated Double Bonds. Organic Sulfur Compounds. Organosilicon Compounds. Organophosphorous Compounds. Aromatic and Heteroaromatic Rings. Selected Infrared and Raman Spectra. Appendices. Index.

3,927 citations


Journal ArticleDOI
TL;DR: In this paper, the average radius of the Ge microcrystals in SiO2 was determined by means of Raman spectroscopy and high resolution electron microscope, which is consistent with quantum confinement of electrons and holes.
Abstract: Ge microcrystals embedded in SiO2 glassy matrices were formed by a radio‐frequency magnetron cosputtering technique and then annealed at 800 °C for 30 min. The average radius of the Ge microcrystals in SiO2 was determined to be about 3 nm by means of Raman spectroscopy and high resolution electron microscope. The annealed sample showed a strong room temperature luminescence with a peak at 2.18 eV. This is consistent with quantum confinement of electrons and holes.

573 citations


Journal ArticleDOI
TL;DR: In this paper, the vibrational Raman and infrared spectra for chemically separated C 60 and C 70 fullerenes were reported and compared with the calculated spectrum for buckminsterfullerene.

554 citations


Journal ArticleDOI
TL;DR: Fang et al. as mentioned in this paper showed that if the methyl C-H peak is split by the methylene group, then the splitting is too small to detect in this experiment, thus weakening the trans bond.
Abstract: trans to the lone pair, thus weakening the trans bond. Similar effects have been seen previously in m e t h ~ l a m i n e ~ ~ and trimethylamine?’a If the methyl C-H peak is split by the methylene group, then the splitting is too small to detect in this experiment. Thus, in terms of overtone spectroscopy, the nitrogen lone pair significantly influences the methylene hydrogens but not the methyl hydrogens. In addition, the anisotropic environment that the methylene group provides for the methyl group apparently does not affect the methyl group absorption. The two-point harmonic frequencies and anharmonicities calculated for these absorptions compare well among analogous bonds in these molecules and with similar modes in other molecules. There are two N-H stretching peaks in the overtone spectrum, one a t higher frequency corresponding to the N-H trans to a methylene hydrogen and one at lower frequency corresponding to the N-H trans to the N-C bond. This agrees with earlier results on diethylamine and di~nethylamine.~~ The large number of C-H bonds in triethylamine makes detailed analysis of its spectra difficult, especially without accompanying data on deuterated analogues. There are a t least two C-H peaks in the overtone spectra, the one at higher frequency being a methyl absorption, while the one a t lower frequency is a methylene absorption. Data for both of these absorptions were fit to a BirgeSponer plot and the resulting parameters compare well to the data of Fang et al. for dieth~lamine.’~

485 citations


Journal ArticleDOI
01 Jan 1991
TL;DR: In this article, the C-T model for bacteriorhodopsin has been integrated into an explicit molecular model for proton pumping in the retinal chromophore of a retinal-containing protein that functions as a light-driven proton pump.
Abstract: Bacteriorhodopsin is a retinal-containing protein that functions as a light-driven proton pump. Resonance Raman and femtosecond dynamic absorption spectroscopy are being used to elucidate the molecular mechanism of bacteriorhodopsin. The primary photochemical process is atrans- to-cis isomerization about the C13=C14 bond of the retinal chromophore that has been directly observed using femtosecond dynamic absorption spectroscopy. The excited state isomerization dynamics can be quantitatively analyzed using a new theory for nonstationary state spectroscopy. Resonance Raman vibrational spectroscopy has been used to determine the structure of the chromophore in each of bacteriorhodopsin’s intermediates and to analyze the kinetics of the photocycle. These results are integrated into an explicit molecular model (the C-T Model) for proton pumping in bacteriorhodopsin.

450 citations


Journal ArticleDOI
TL;DR: In this article, surface Raman scattering is used to study self-assembled monolayers formed from a series of 1-alkanethiol s, CH3(CH2)^SH, where n = 3-5, 7, 8,11, and 17, at mechanically polished and electrochemically roughened Au surfaces.
Abstract: Surface Raman scattering is used to study self-assembled monolayers formed from a series of 1-alkanethiol s, CH3(CH2)^SH, where n = 3-5, 7, 8,11, and 17, at mechanically polished and electrochemically roughened Au surfaces. Defect structure in these films is investigated by use of the relative intensities of peaks due to trans and gauche conformations in the v(C-S) and P(C-C) frequency regions. Surface selection rules for Raman spectroscopy are used to estimate orientation of the alkanethiol layers at Au. The orientation proposed on the basis of the Raman spectral data is consistent with those previously reported on the basis of other measurements at Au surfaces. This orientation is compared to that previously determined for these films at Ag. Alkanethiols at Ag are found to have a chain tilt from the surface normal less than the 30° previously reported for Au. The C-S bond is found to be perpendicular to the Ag surface while it is largely parallel to the surface at Au. Differences in the spectra of short-chain alkanethiols from smooth and rough surfaces are attributed to disordering of the film at the roughened Au surface which occurs predominantly near the S end of the molecule on rough Au surfaces.

411 citations



Journal Article
TL;DR: The 29 Si and 23 Na NMR, Raman and infrared spectra of glasses quenched from liquids at pressures up to 12 GPa for three alkali silicate compositions (Na 2 Si 2 O 5, Na 2 Si 4 O 9, K 2 Si O 9 ) and silica (SiO 2 ) reveal systematic changes in the melt structure with pressure.
Abstract: The 29 Si and 23 Na NMR, Raman, and infrared spectra of glasses quenched from liquids at pressures up to 12 GPa for three alkali silicate compositions (Na 2 Si 2 O 5 , Na 2 Si 4 O 9 , K 2 Si 4 O 9 ) and silica (SiO 2 ) reveal systematic changes in the melt structure with pressure. The most novel change is the occurrence of [5] Si and [6] Si species at high pressures identified by peaks in the 29 Si MAS NMR spectra of the alkali silicate glasses. -from Authors

287 citations


Journal ArticleDOI
TL;DR: The frequency and line shape of the diamond Raman line are examined in detail for a series of microwave-plasma-assisted chemical-vapor-deposition films grown on Si and it is concluded that the observed shifts do notmore arise from phonon confinement alone and arise primarily from compressive stress.
Abstract: The frequency and line shape of the diamond Raman line are examined in detail for a series of microwave-plasma-assisted chemical-vapor-deposition films grown on Si. The Raman lines in the films appear at higher frequency (shifts of up to 3 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) than that of natural diamond and the observed lines are symmetric with broader linewidths than that of natural diamond, ranging from 5.7 to 17.1 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. In addition, the line frequencies and linewidths are correlated; the films with the highest vibrational frequencies have the largest linewidths. The data include single-point measurements on eight films grown under different conditions as well as 500 data points from different positions on a single film that were obtained in a spatially resolved Raman experiment. Several mechanisms for the frequency shift and the correlation of the linewidth with frequency are considered including phonon confinement, residual stress, and defect scattering. Contrary to the observations, Raman line shapes computed from the phonon-confinement model (which has been used successfully to model Raman scattering in microcrystalline Si and GaAs), using phonon-dispersion curves for diamond from the literature, are highly asymmetric at the linewidths observed. It is concluded that the observed shifts in the diamond Raman line do not arise from phonon confinement alone and arise primarily from compressive stress. The line broadening also is not produced by phonon confinement alone and may arise from decreasing phonon lifetime associated with scattering from defects or from an inhomogeneous stress distribution in the films. The observed correlation between Raman line frequency and width suggests that the degree of compressive stress may be associated with the density of microcrystalline defects.

258 citations


Journal ArticleDOI
TL;DR: In this article, far-infrared and Raman spectroscopic studies were performed on compounds of composition A2BCX4 (A = Cu, Ag; B = Zn, Cd, Hg, Mn, Fe, Co; C = Si,

251 citations


Journal ArticleDOI
TL;DR: In this paper, Raman and infrared spectroscopies have been employed to probe the continuous evolution of borate glass structures as a function of the nature and concentration of alkali oxide modifier.

Journal Article
TL;DR: In this paper, the spectral properties and changes with crystallinity of natural graphite were analyzed using Raman micro-spectroscopy, showing that the Raman spectrum is a sensitive monitor of changes in graphite crystallinity, reflecting conditions from greenschist-to granulite-facies metamorphism.
Abstract: This study demonstrates the usefulness of Raman microspectroscopy an evaluation of the crystallinity of graphite in natural samples. The sensitivity obtained is at least as good as that for X-ray diffractometry. Laser Raman microprobe analyses of graphite separates, mostly from suites of regionally metamorphosed carbon-bearing pelites (Grew 1974), show that l) the spectra oferaphite accurately reflect the degree of crystallinity in terms of the (001) inplane crystallite size, 2) the same spectral features and changes with crystallinity occur in the spectra of natural graphite as in those of synthetic samples, 3) the Raman spectrum is a sensitive monitor of changes in graphite crystallinity, reflecting conditions from greenschist- to granulitefacies metamorphism, 4) significant changes in the Raman spectral profile coincide with transitions in the metapelites that delineate the chlorite, biotite + garnet, staurolite -r. kyanite + andalusite, and sillimanite zones, and 5) the graphite stmcture apparently records only the peak metamorphic temperatures and does not recrystallize under retrograde conditions.


Journal ArticleDOI
TL;DR: In this article, the structure of glasses in the CaO�Al2O3SiO2 (CAS) and MgOAl 2O3-6-1 SiO2 systems have been studied using Raman and infrared (IR) reflectance spectroscopies.
Abstract: The structure of glasses in the CaOAl2O3SiO2 (CAS) and MgOAl2O3SiO2 (MAS) systems have been studied using Raman and infrared (IR) reflectance spectroscopies. Kramers-Kronig analysis was performed on the IR data. Two compositional series were chosen in each system, one which has a constant average polymerization of 1 non-bridging oxygen per tetrahedral cation, and the other in which silica content is constant at 50 mol%, but polymerization varies. The results indicate that the presence of alkaline earth network modifiers favors the formation of species with high negative charge density. In the NBO/T = 1 series this leads to the equilibrium 2Q3 = Q4 + Q2 (where the superscript is the number of bridging oxygens per tetrahedron) shifting to the right at low Al content and to the left at high Al/Si. In the fully polymerized, 50% silica Mg glass, there is evidence of clustering into Al-rich and Si-rich domains. Transformation of the IR data yields a well-resolved low-frequency band in the CAS spectra whose frequency depends on polymerization and whether Ca is acting as a network modifier or charge balancer. The analogous Mg band is apparently buried in the mid-frequency network mode.

Journal ArticleDOI
TL;DR: The pyrolysis of a PCS precursor has been studied up to 1600 °C through the analysis of the gas phase and the characterization of the solid residue by thermogravimetric analysis, extended X-ray absorption fine structure, electron spectrocopy for chemical analysis, transmission electron microscopy, Xray diffraction, Raman and Auger electron spectroscopy microanalyses, as well as electrical conductivity measurements.
Abstract: The pyrolysis of a PCS precursor has been studied up to 1600 °C through the analysis of the gas phase and the characterization of the solid residue by thermogravimetric analysis, extended X-ray absorption fine structure, electron spectrocopy for chemical analysis, transmission electron microscopy, X-ray diffraction, Raman and Auger electron spectroscopy microanalyses, as well as electrical conductivity measurements. The pyrolysis mechanism involves three main steps: (1) an organometallic mineral transition (550 < T p < 800 °C) leading to an amorphous hydrogenated solid built on tetrahedral SiC, Si02 and silicon oxycarbide entities, (2) a nucleation of SiC (1000 < T p < 1200 °C) resulting in SiC nuclei (less than 3 nm in size) surrounded with aromatic carbon layers, and (3) a SiC grain-size coarsening (T p > 1400 °C) consuming the residual amorphous phases and giving rise simultaneously to a probable evolution of SiO and CO. The formation of free carbon results in a sharp insulator-quasimetal transition with a percolation effect.

Patent
03 Apr 1991
TL;DR: In this article, the authors proposed a method for distinguishing between calcified atherosclerotic tissue and normal cardiovascular tissue using Fourier transform Raman spectrum, which is distinguishable from analagous spectra obtained from human aortic tissue.
Abstract: A method for distinguishing between calcified atherosclerotic tissue and either fibrous atherosclerotic tissue or normal cardiovascular tissue. The present method is based on the discovery that, when irradiated with a beam of monochromatic infrared light, calcified atherosclerotic human aortic tissue produces a Fourier Transform Raman spectrum which is distinguishable from analagous spectra obtained from fibrous atherosclerotic human aortic tissue and normal human aortic tissue. Some salient differences in the respective Raman spectra are the presence of five Raman bands at Raman shifts of 957, 1071, 1262-1300, 1445, and 1659 cm-1 (±4 cm-1 for all shifts) for the calcified tissue as compared to three Raman bands at Raman shifts of 1247-1270, 1453 and 1659 cm-1 (±4 cm-1 for all shifts) for the fibrous tissue and three Raman bands at Raman shifts of 1247-1270, 1449 and 1651 cm-1 (±4 cm-1 for all shifts) for the normal tissue. In addition, it was discovered that the ratios of intensities for the Raman bands at 1659 and 1453 cm-1 and at 1254 and 1453 cm-1 were 0.69 and 0.53, respectively, for the calcified tissue, 1.02 and 0.85, respectively, for the fibrous tissue and 1.2 and 0.83, respectively, for the normal tissue.

Book
01 Jan 1991
TL;DR: In this article, modern Raman Instrumentation and Techniques Experimental Considerations for Accurate Polarization Measurements Raman Spectroscopy of Inorganic Species in Solution Quantitative Analysis by Raman-Spectroscopy Characterization of Semiconductors by RMS by RRS and Synthetic Organic Polymers Anisotropic Scattering Properties of Uniaxially Oriented Polymers.
Abstract: Modern Raman Instrumentation and Techniques Experimental Considerations for Accurate Polarization Measurements Raman Spectroscopy of Inorganic Species in Solution Quantitative Analysis by Raman Spectroscopy Characterization of Semiconductors by Raman Spectroscopy Raman Spectra of Synthetic Organic Polymers Anisotropic Scattering Properties of Uniaxially Oriented Polymers: Raman Studies Organic and Petrochemical Applications of Raman Spectroscopy Raman Spectroscopy in Heterogeneous Catalysts Raman Spectroscopy for Biological Applications Chemical Applications of Gas-Phase Raman Spectroscopy.

Book
01 Jan 1991
TL;DR: In this paper, a comparison of electrodes and electrographs is presented for the study of Solid Ionic Conductors Ellipsometry as an In-Situ Probe for Study of Electrode Processes.
Abstract: STRUCTURE AND COMPOSITION OF ELECTRODES AND ELECTROLYTES: Techniques for the Study of Solid Ionic Conductors Ellipsometry as an In Situ Probe for Study of Electrode Processes In Situ Characterization of Electrode Processes by Photothermal Deflection Spectroscopy Surface X-Ray Absorption Spectroscopy, EXAFS and NEXAFS for the In Situ and Ex Situ Study of Electrodes Surface-Enhanced Raman Spectroscopy In Situ Characterization of Electrodes by Neutron Scattering Diffraction Techniques for Determining the Structure of Electrolytes in the Liquid Phase Moessbauer Spectroscopy Laser Interferometry Study of Mass Transport Limitation in Electro-Deposition of Metals/Polymers. ELECTROCHEMICAL MEASUREMENT TECHNIQUES: An Introduction to Electrochemistry in Molten Salts Application of Electrochemical Impedance Spectroscopy in Electrochemistry and Corrosion Science Electrochemical Impedance Spectroscopy (EIS)- Application in Corrosion Science and Technology Numerical Techniques for Modeling Current Distribution at Plane or Flow-By Electrodes Experimental Simulation of Porous Electrodes Techniques for Study of Nucleation during Metal Electrodisposition.

Journal ArticleDOI
TL;DR: In this paper, the growth of Ge microcrystals in SiO2-Ge mixture films prepared by an rf co-sputtering method was studied by Raman spectroscopy and electron microscopy.
Abstract: The growth of Ge microcrystals in SiO2-Ge mixture films prepared by an rf co-sputtering method was studied by Raman spectroscopy and electron microscopy. It was found that in the as-deposited films, Ge clusters about 2 nm in diameter are embedded in SiO2 matrices and they are grown to Ge microcrystals by thermal annealing. It is shown that annealing at 800°C is necessary to prepare well-grown microcrystalline samples. The microcrystalline size dependence of the Raman spectrum was investigated. The increase in the linewidth observed with decreasing the size can be well explained by the phonon confinement theory, while the downward shift of the peak frequency predicted from the theory was not observed, presumably due to the stress caused by SiO2 matrices.


Journal ArticleDOI
TL;DR: The most plausible explanation seems to be that the sample degradation is the result of photochemical reactions initiated by laser excitation at 514.5 nm of as yet unidentified sensitizer molecules or complexes present in chromosomes and cells but not in purified DNA and histone protein samples.

Journal Article
A. Chopelas1
TL;DR: In this paper, a single crystal Raman spectra of the fundamental modes offorsterite (Mg2Si04), olivine (M&.88,Feo.12), fayalite (Fe 2Si04, and monticellite (CaMgSi04) was presented.
Abstract: Polarized single crystal Raman spectra of the fundamental modes offorsterite (Mg2Si04), olivine (M&.88,Feo.12),fayalite (Fe2Si04), and monticellite (CaMgSi04) are presented. Seven low energy modes «450 cm-I) in forsterite differ from those of all previous studies. All modes predicted by symmetry for forsterite and monticellite were observed; 34 out of 36 modes were observed for fayalite. Assignment of the modes was determined by systematics in frequency changes resulting from cation substitution. Although the lattice modes are generally mixed, likely mode assignments are made using the following observations. The lowest energy modes are assigned to Si04 translations and appear to be mixed with the cation translations. The lattice modes between 330 and 435 cm-I in forsterite that changed the least with composition were assigned as Si04 rotations. The modes from 300 to 390 cm-I that showed the greatest variation with composition or showed signs of two-mode behavior in the olivine Mg88were assigned as M2 translations. The Si04 internal stretching and bending modes were assigned to the highest frequencies; they vary little from forsterite to monticellite to fayalite and appear to depend more on cation mass than volume. These assignments are consistent with previous single-crystal infrared studies of forsterite and fayalite and with mode Griineisen parameters 'Yimeasured vs. pressure in that the highest 'Yivalues should be associated with the M2 cations and the lowest with the Si04 internal modes. INTRODUCTION important modes are those below 450 cm-I, as the estiThe vibrational modes of olivines, important geophysmat~s of heat capacity and entropy vs. tem~~rature at ical and cosmochemical phases, have been studied extenambIent temperatures and below are very sensItIve to the sively by Raman spectroscopy (Iishi, 1978; Servoin and number of these mo~es and their distribution. These are, Piriou, 1973; Piriou and McMillan, 1983; Stidham et aI., h,owever, the most dIfficult to measure because of exten1976; Hohler and Funck, 1973; Chopelas, 1990), infrared ~IV~over~apping: breadth ofp~aks a~~ t~o-mode behavspectroscopy (Hofmeister, 1987. Tarte 1963. Paqueslor In sohd solutIons, and low IntensItIes In Raman specLedent and Tarte, 1973; Kovach 'et aI., 1'975; Hofmeister tra because ~f the low polarizabilities of the octahedral et aI., 1989; plus some references given above for Raman structural unIts. spectroscopy), inelastic neutron scattering (Rao et aI., T~e polarized ,Raman spectrum of forsterite has been 1988), and lattice dynamical calculations (Price et aI., prevl0.u~ly descnbe~ (~ohler and Funck, 1973; Servoin 1987a, 1987b). Study of these properties yields insight and Plnou, 1973; IIS~I, 1978), bu~ none, of the results into the interatomic forces within the crystal structure agree for the ~r~qUencies o,f the low IntensIty modes. The and a basis for understanding the effect of cation substionly other ohvlne for whIch a (nearly) complete singletutions on the thermodynamic properties. For example, crystal, Rama~ spectrum has been des~ribed is tephroi,te the heat capacity and entropy can be estimated to better (Mn2SI04) (StIdham et aI., 1976); partIal data are avallthan 50/0over a moderate temperature range (, , 500 K, a~l~ for Ca-beari~g phases (e.g., ~ohler and Funck, 1973; Kieffer, 1979) from the mode frequency information ob~lnou and McMIllan, 1983). ThIS study was prompted, tained by infrared and Raman spectroscopy. The accuIn part, by the general lack of Raman data in the low racy in estimating these quantities can increase to better frequency range for other olivines and, in part, by disthan 0.5% over a larger temperature range (> 1000 K) if crepancies with the previously reported data for forsterite all of the infrared and Raman modes are enumerated and (Chopelas, 1990). assigned to atomic motions. The detailed mode assignIn this study, single-crystal polarized Raman spectra of ments provide an accurate method for estimating the freforsterite, olivine (Mgo.88,Feo.12)2Si04,monticellite, and quencies of inactive or unobserved modes, thereby yieldfayalite are presented. Mode assignments to molecular ing more precise information on the frequency distribution motions are made by comparison of analogue modes in or density of states (see Hofmeister, 1987; Hofmeister these olivines and previous results of tephroite (Stidham and Chopelas, 1991a; Chopelas, 1990, 1991). The most et aI., 1976) and 'Y-Ca2Si04 (Piriou and McMillan, 1983). 0003-004X/91/0708-1101$02.0

Journal ArticleDOI
TL;DR: A review of the literature relating to the application of surfaceenhanced Raman scattering (SERS) and surface-enhanced resonance (SERRS) techniques to the study of biological molecules is presented in this paper.
Abstract: This review summarizes the literature relating to the application of surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) techniques to the study of biological molecules. The emphasis is on publications that have appeared during the period from 1985 to 1991. The review is divided into six major parts. First, a brief overview of the current understanding of the mechanistic aspects of SERS/SERRS is given, with an emphasis on the relationship between theoretical predictions and experimental results. The most common experimental systems (colloids, metal island films, and electrodes) are described. Studies of biological systems are described in the second (small molecules), third (DNA and proteins) and fourth (membranes proteins and membrane preparations) sections. In the fifth or conclusion section, the potential use of SERS or SERRS as a method for obtaining spectra of native biological molecules is evaluated. Finally, the sixth section describes advances in Raman instrumentation in terms of their possible impact on future applications of SERS/SERRS techniques to biological molecules.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the solid state Raman scattering spectra of a homologous series of linear polyenes, with the number of alternated double bonds varying from 3 to 12.
Abstract: We have measured the solid state Raman scattering spectra of a homologous series of linear polyenes, with the number of alternated double bonds varying from 3 to 12. While we find a linear dependence of the Raman shifts of resonantly coupled modes with inverse conjugation length, we have also followed the suggestion of previous work in examining the inverse square product of the several Raman frequencies as a function of the logarithm of the measured energy gap of the molecule. This provides a linear relationship, as found for trans‐polyacetylene, a result which is qualitatively consistent with the amplitude mode model of Horovitz and co‐workers. We also find, consistent with previous work on polyacetylene, a monotonic decrease in the ratios of oscillator strengths of the two strongest bands with conjugation length, as recently predicted by a series of molecular dynamics calculations. Suggested interpretations of a number of qualitative observations, including splitting of modes for shorter conjugation le...

Journal ArticleDOI
TL;DR: In this paper, the relationship between phonon Raman spectra and structure was established and illustrated with natural diamond, graphite, carbon, novel brilliants and novel ultrahard substances.

Journal ArticleDOI
TL;DR: In this article, the electronic contribution to surface+nhanced Raman scattering (SERS) is quantitatively separated from classical electromagnetic enhancement, and various experimental results for the chemical specificity and vibration selectivity of SERS are presented.
Abstract: Lehrstuhl ftir Oberflilchenwissenschaft (IPkM), Heinrich-Heine-Universitiit Diisseldo4,t000 Diisseldorf, Germany This review concentretes on the electronic contribution to surface+nhanced Raman scattering (SERS). This socalled .chemicel efrect' is quantitatively separeted from classical electromagnetic enhancement. It proceeds by increesed electrorphoton coupling at an atomicelly rough surface and by temporary charge transfer to edsorbate orbitals. These .oo".pt ".. roppo.ted by various experimental results. The model sccounb for the chemical specificity and vibrationel selectivity of SERS and (partty) for the 'SERS specificity' of vsrious metals.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the excitation is attributed to an electronically induced displacement of the ion equilibrium coordinates, rather than a direct Raman excitation mechanism is not responsible for coherent phonon generation.
Abstract: Coherent phonons in Sb, Bi, Te, and Ti2O3 can be generated impulsively, and detected in the time domain through reflectivity modulation using 60 fs pulses of laser light at 2 eV. Experimental data for these opaque solids suggest that a direct Raman excitation mechanism is not responsible for coherent phonon generation. Rather, the excitation is attributed to an electronically induced displacement of the ion equilibrium coordinates.

Journal ArticleDOI
19 Apr 1991-Science
TL;DR: A laser method based upon carbon ion implantation and pulsed laser melting of copper has been used to produce continuous diamond thin film, which confirmed the films to be defect-free single crystal over large areas of up to several square micrometers with no grain boundaries.
Abstract: A laser method based upon carbon ion implantation and pulsed laser melting of copper has been used to produce continuous diamond thin film. Carbon ions were implanted with ion energies in the range of 60 to 120 keV, and doses of 1.0 x 1018 to 2.0 x 1018 ions cm–2. The ion-implanted specimens were treated with nanosecond excimer laser pulses with the following parameters: energy density, 3.0 to 5.0 J cm–2; wavelength, 0.308 µm; pulse width, 45 nanoseconds. The specimens were characterized with scanning electron microscopy (SEM), x-ray diffraction, Rutherford backscattering/ion channeling, Auger, and Raman spectroscopy. The macroscopic Raman spectra contained a strong peak at 1332 cm–1 with full width at half maximum of 5 cm–1, which is very close to the quality of the spectra obtained from single-crystal diamond. The selected area electron diffraction patterns and imaging confirmed the films to be defect-free single crystal over large areas of up to several square micrometers with no grain boundaries. Low voltage SEM imaging of surface features indicated the film to be continuous with presence of growth steps.

Journal ArticleDOI
TL;DR: In this article, the authors used factor group analysis and correlating the bands by their intensities to assign the SiO4 internal motions, as a rotation, or to a type of translation.
Abstract: Infrared reflectance (IR) and Raman spectra were collected on small (ca. 500 micron) single crystals of 5 natural garnets with nearly end-member compositions: pyrope (98% Mg3Al2Si3O12), almandine (83% Fe3Al2Si3O12), spessartine (98% Mn3Al2Si3O12), grossular (97% Ca3Al2Si3O12), and andradite (99% Ca3Fe2Si3O12). Frequencies and symmetry assignments were determined for all 17 IR modes and all 25 Raman modes. By using factor group analysis and by correlating the bands by their intensities, bands were assigned to either one of the SiO4 internal motions, as a rotation, or to a type of translation. The assignments are supported by (1) the distinct trends of frequencies with cell size and cation masses for each of the different types of motion, (2) the similarity of garnet energies for each of the different types of motion to those of olivine with the same cation, and (3) the closeness of the T1u IR frequencies to the T2g Raman frequencies. Mode mixing appears to be weak. Correlations between frequencies and structural parameters suggests a direct dependence of force constants on lattice parameter. This relationship arises from bond lengths in the garnet structure being constrained by the size and compressibility of adjacent polyhedra through edge-sharing. Comparison of our endmember data with previous powder IR studies of intermediate garnets indicates that dodecahedral (X) and octahedral (Y) sites alone exhibit two-mode behavior for those solid solutions involving two ions with considerably different masses. However, for solid solutions involving cations of much different ionic radii, two-mode behavior is found for the translations of SiO4 groups. This is the first report of two-mode behavior that is unrelated to mass, and instead is due to significantly different force constants in the pyralspites compared to the ugrandites.

Journal ArticleDOI
TL;DR: In this paper, the FTIR and laser Raman spectra of benzimidazole have been recorded and the observed frequencies were assigned to various modes of vibrations on the basis of normal coordinate calculations, assuming C s point group symmetry.