Showing papers on "Raman spectroscopy published in 1983"

The structure of high-silica alkali-silicate glasses. A Raman spectroscopic investigation

Abstract: Normal Raman spectra of xM2O · (100 − x)SiO2 glasses (M = Li, Na, K, Rb, Cs and x = 0, 5, 10, 15, 20, 25, 30) and differential Raman spectra of the 5, 10, and 15% M2O glasses are presented. The Raman spectra reflect distinct structural differences in the silicate networks of these glasses caused by the presence of different alkali cation types. The structural origin and localization of vibrational modes producing characteristic spectral bands of these glasses are discussed. Bands in the 900–1200 cm−1 region of the spectra of the alkali-silicated glasses result from highly localized Si-nonbridging oxygen stretching modes and relative intensities of these bands may be used to determine alkali distributions around SiO4 tetrahedra. Comparison of the Raman Spectra of the alkali-silicate glasses has shown that smaller alkali cations exhibit a greater tendency than their larger counterparts to cluster in pairs around SiO4 tetrahedra in these glasses, even at low alkali contents. The high frequency spectral features at 1100 and 1150 cm−1 also indicate the presence of two distinct structural environments in which an SiO4 tetrahedron contains one nonbridging oxygen in all alkali-silicate glasses containing ⩽ 25% M2M except those containing lithium. Intensity of the low frequency spectral band at 440 cm−1 indicates that regional alkali clustering such as that required for phase separation is also more prevalent in glasses containing smaller alkali cations. It is proposed that modeling of the silicate structure in alkali-silicate glasses must account for both long-range and localized alkali cation distribution.

The enhancement of Raman scattering, resonance Raman scattering, and fluorescence from molecules adsorbed on a rough silver surface

Abstract: The enhancements of normal Raman scattering, resonance Raman scattering, and fluorescence from molecules adsorbed on identical, well‐characterized, silver‐island films are reported. The enhancement arises from the electromagnetic interaction between the molecules and the electronic plasma resonance of the silver islands. A hierarchy of enhancement ratios is found, with typical values of 105 for RS, 103 for RRS and 10−1 to 10 for fluorescence, depending on the quantum yield of the molecular fluorescence. A model, developed on heuristic grounds and substantiated using the density matrix formalism, describes the light scattering processes and the effects of the plasma resonance. This model presents a unified picture of the surface‐induced enhancement effects and is consistent with the experimental values. The comparison of all the forms of optical scattering leads to a complete determination of the role of the plasma resonances in the various portions of the scattering process. The excitation of the electronic plasma resonance results in an increased local field at the molecules leading to an increased excitation or absorption rate. Similarly, the excitation of the plasma resonance by the molecular emission dipole results in an increase in the radiative decay rate. However, the electromagnetic coupling of the molecule to the plasma resonance also adds an additional damping channel which can result in a reduction of the absorption or excitation rate as well as the emission yield. The resultant balance of these processes leads to the hierarchy in the measured enhancements. The hierarchy of enhancements is also shown to have important spectroscopic consequences.

Laser processing and analysis of materials

Abstract: 1 Lasers and Laser Radiation.- 1.1. Introduction.- 1.2. Laser Sources.- 1.2.1. Ruby Laser.- 1.2.2. Nd-YAG Laser.- 1.2.3. Nd-Glass Laser.- 1.2.4. Tunable Infrared Diode Lasers.- 1.2.5. Helium-Neon Laser.- 1.2.6. Argon and Krypton Ion Lasers.- 1.2.7. Helium-Cadmium Laser.- 1.2.8. CO2 Laser.- 1.2.9. Rare Gas Halide Lasers.- 1.2.10. Dye Lasers.- 1.2.11. Stimulated Raman Scattering.- 1.3. Laser Radiation.- 1.3.1. Monochromaticity.- 1.3.2. Beam Shape.- 1.3.3. Beam Divergence.- 1.3.4. Brightness.- 1.3.5. Focusing of Laser Radiation.- 1.3.6. Coherence.- 1.4. Lens Aberrations.- 1.4.1. Spherical Aberration.- 1.4.2. Coma.- 1.4.3. Astigmatism.- 1.4.4. Field Curvature.- 1.4.5. Distortion.- 1.5. Window Materials.- 1.6. Mirrors and Polarizers.- 1.7. Q-Switching.- 1.7.1. Acousto-Optical Q-Switches.- 1.7.2. Electro-Optical Q-Switches.- 1.7.3. Passive Q-Switching.- 1.8. Frequency Conversion.- 1.9. Mode Locking.- 1.10. Detectors and Power Meters.- 1.10.1. Power Meters.- 1.10.2. Radiation Detectors.- 2. Materials Processing.- 2.1. Absorption of Laser Radiation by Metals.- 2.2. Absorption of Laser Radiation by Semiconductors and Insulators.- 2.3. Thermal Constants.- 2.4. Laser Drilling: Heat Transfer.- 2.4.1. Heating without Change of Phase.- 2.4.2. Heating with Change of Phase.- 2.4.3. Experimental.- 2.5. Welding.- 2.5.1. Heat Transfer-Penetration Welding.- 2.5.2. Heat Transfer-Conduction Welding.- 2.5.3. Welding with Multikilowatt Lasers.- 2.5.4. Welding with Low-Power Lasers.- 2.5.5. Laser Spot Welding.- 2.6. Cutting.- 2.6.1. Heat Transfer.- 2.6.2. Cutting Metals.- 2.6.3. Cutting Nonmetals.- 2.6.4. Scribing and Controlled Fracture.- 2.7. Micromachining.- 2.7.1. Resistor Trimming.- 2.7.2. Machining of Conductor Patterns.- 2.7.3. Fabrication of Gap Capacitors.- 2.7.4. Image Recording.- 2.7.5. Laser Marking.- 2.7.6. Micromachining-Thermal Considerations.- 2.8. Surface Hardening.- 2.9. Surface Melting, Alloying, and Cladding.- 2.10. Surface Cleaning.- 2.11. Crystal Growth.- 2.12. Optical Fiber Splicing.- 2.12.1. Optical Fiber-End Preparation.- 2.12.2. Optical Fiber-Drawing.- 2.13. Laser Deposition of Thin Films.- 2.13.1. Evaporation.- 2.13.2. Electroplating.- 2.13.3. Chemical Vapor Deposition.- 2.13.4. Photodeposition and Photoetching.- 3 Laser Processing of Semiconductors.- 3.1. Introduction.- 3.2. Annealing.- 3.3. Annealing-CW Lasers.- 3.4. Recrystallization.- 3.5. Silicide Formation.- 3.6. Ohmic Contacts and Junction Formation.- 3.7. Device Fabrication.- 3.8. Electrical Connections on Integrated Circuits.- 3.9. Monolithic Displays.- 4 Chemical Processing.- 4.1. Introduction.- 4.2. Schemes for Laser Isotope Separation.- 4.3. The Enrichment Factor.- 4.4. Laser-Induced Reaction.- 4.5. Single-Photon Predissociation.- 4.6. Two-Photon Dissociation.- 4.7. Photoisomerization.- 4.8. Two-Step Photoionization.- 4.9. Photodeflection.- 4.10. Multiphoton Dissociation.- 4.10.1. Deuterium.- 4.10.2. Boron.- 4.10.3. Carbon.- 4.10.4. Silicon.- 4.10.5. Sulfur.- 4.10.6. Chlorine.- 4.10.7. Molybdenum.- 4.10.8. Osmium.- 4.10.9. Uranium.- 4.11. Selective Raman Excitation.- 4.12. Economics of Laser Isotope Separation.- 4.13. Laser-Induced Reactions.- 4.13.1. Infrared Photochemistry-Basic Mechanisms.- 4.13.2. Vibrationally Enhanced Chemical Reactions.- 4.13.3. Vibrationally Induced Decomposition.- 4.14. Isomerization.- 4.15. Lasers in Catalysis.- 4.16. Laser-Induced Reactions: UV-VIS Excitation.- 4.17. Processing via Thermal Heating.- 4.18. Polymerization.- 5 Lasers in Chemical Analysis.- 5.1. Introduction.- 5.2. Absorption Spectroscopy.- 5.2.1. Absorption vs. Other Techniques.- 5.2.2. Intracavity Absorption.- 5.3. Laser-Induced Fluorescence.- 5.3.1. Laser-Induced Fluorescence: Theory.- 5.3.2. Laser-Excited Atomic Flame Fluorescence.- 5.3.3. Laser-Excited Molecular Flame Fluorescence.- 5.3.4. Beam Diagnostics.- 5.3.5. Fluorimetry and Phosphorimetry.- 5.3.6. Selective Excitation of Probe Ion Luminescence.- 5.4. Laser-Enhanced Ionization Spectroscopy.- 5.5. Multiphoton Ionization.- 5.6. Raman Spectroscopy.- 5.6.1. Theory and Physical Principles.- 5.6.2. Experimental Techniques.- 5.6.3. Experimental Results.- 5.6.4. Coherent Anti-Stokes Raman Spectroscopy.- 5.7. Laser Magnetic Resonance.- 5.8. Laser Photoacoustic Spectroscopy.- 5.8.1. LPS of Gases.- 5.8.2. LPS of Liquids and Solids.- 5.8.3. Photoacoustic Imaging.- 5.9. Laser Microprobe.- 5.10. Atomic Absorption Spectrometry.- 5.11. Laser Microprobe Mass Spectrometer.- 5.12. Laser Raman Microprobe.- 5.13. Lasers in Chromatography.- 6 Lasers in Environmental Analysis.- 6.1. Propagation of Laser Radiation through the Atmosphere.- 6.2. Laser Remote Sensing of the Atmosphere.- 6.2.1. Absorption Measurements.- 6.2.2. LIDAR.- 6.2.3. Laser Remote Sensing of Wind Velocity.- 6.2.4. Raman LIDAR.- 6.2.5. Differential Absorption LIDAR (DIAL).- 6.2.6. Resonance Fluorescence.- 6.2.7. Heterodyne Detection.- 6.3. Laser Sampling of Aerosols.- 6.3.1. Particle Size and Distribution.- 6.3.2. Particle Composition.- 6.3.3. Interaction of High-Power Laser Radiation with Aerosol Particles.- 6.4. Laser Remote Sensing of Water Quality.- References.- Materials Index.

Dependence on volume of the phonon frequencies and the ir effective charges of several III-V semiconductors

Abstract: The mode Gr\"uneisen parameters of the LO and TO Raman phonons of AlN, BN, and BP, and the dependence of ${e}_{T}^{*}$ on lattice constant have been measured by Raman scattering in a diamond anvil cell. The results for ${e}_{T}^{*}$ are interpreted by means of pseudopotential calculations of ${e}_{T}^{*}$ versus lattice constant.

Raman spectroscopy of calcium aluminate glasses and crystals

Abstract: Solar furnace melting and fast-quench techniques have been used to prepare calcium aluminate glasses from 75 mol% CaO to 82 mol% Al2O3, which have been studied by Raman spectroscopy. The CaAl2O4 glass spectrum may be interpreted in terms of a fully-polymerized network of tetrahedral aluminate units, which is depolymerized on addition of CaO component analogous to binary silicate systems. The spectra of glasses with higher alumina content than CaAl2O4 may not be simply interpreted and a structural model is proposed which would be consistent with the glass spectra and with observed crystal structures along the CaAl2O4Al2O3 join. This model suggests formation of highly condensed aluminate tetrahedral on initial addition of alumina, with the appearance of aluminate polyhedra of higher average coordination at higher alumina content. Similar high coordination polyhedral are also suggested for a limited composition range along the CaOCaAl2O4 join. These interpretations are compared with the results of a previous study in the SiO2Al2O3 glass system.

Rare‐earth titanates and stannates of pyrochlore structure; vibrational spectra and force fields

Abstract: Infrared absorption and polarized Raman spectra of rare-earth titanates of pyrochlore structure Ln2Ti2O7 (Ln = Sm, Gd, Yb; Y) and Ln2Sn2O7 (Ln = La, Sm, Gd, Yb, Lu; Y) have been recorded. A valence force field calculation clearly supports the assignment of the frequencies. A comparison of the results with those of homologous zirconates and hafnates is presented.

High-pressure Raman study of zone-center phonons in PbTi O 3

Abstract: A complete study of the $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}=\stackrel{\ensuremath{\rightarrow}}{0}$ optical phonons of the ferroelectric tetragonal PbTi${\mathrm{O}}_{3}$ as a function of hydrostatic pressure has been carried out using Raman spectroscopy. The coalescence, to the same frequency, of the high-energy [${A}_{1}(\mathrm{TO})$, $E(\mathrm{TO})$] pairs of phonons in the ferroelectric phase and the disappearance of the first-order Raman lines in the cubic phase has enabled us to determine the transition pressure ${P}_{c}$, as well as the second-order character of the phase transition. Our results also suggest the existence of a tricritical point in the ($P$,$T$) phase diagram. Using the Liddane-Sachs-Teller relation we calculate the static dielectric constant as a function of pressure and compare the results with previous dielectric measurements. Moreover, we discuss the soft phonons, their damping, and their behavior near the phase transition. It is found that the soft $E(\mathrm{TO})$ phonon damping function is nearly constant over a wide frequency range and that it appears to diverge near the phase transition.

Surface-enhanced second-harmonic generation and Raman scattering

Abstract: Emission from a variety of surface optical processes is significantly increased at interfaces with roughened noble metals. A general formalism, applicable to any optical process, is used to predict the enhancement in the radiated power for second-harmonic generation and Raman scattering from an electrochemically reformed silver surface. Experimental results for these enhancements at different wavelengths are reported. The intensity of the second-harmonic radiation can be understood strictly in terms of the strong macroscopic electric fields produced at the roughened surface by resonant structures. For Raman scattering, part of the enhancement also arises from microscopic local-field effects and the direct chemical interaction of the adsorbate and substrate. The surface-enhanced second-harmonic and Raman signals are studied as the silver sample undergoes oxidation and reduction in an electrolyte containing cyanide ions. The behavior of these two easily measurable probes is described and correlated with the system's surface chemistry.

Surface Enhanced Raman Scattering by Metal Spheres. I. Cluster Effect

Abstract: An electromagnetic theory for the light absorption by a cluster of metal spheres and the Raman scattering by a molecule adsorbed on it is presented, which takes into account the retardation effect exactly and is applicable to an arbitrary cluster size. The theory is applied to a two-sphere cluster of Ag and Au. It is shown that the absorption spectrum is doubly peaked and the maximum enhancement factor of the Raman intensity amounts to 10 7 ∼10 8 when the distance between spheres is decreased. Absorption spectra of three- and four-sphere clusters are also calculated, which indicate that the essential features of the experimental observations are explained by the two-sphere cluster.

Characterization of DNA structures by Raman spectroscopy: high-salt and low-salt forms of double helical poly(dG-dC) in H2O and D2O solutions and application to B, Z and A-DNA.

Abstract: Raman spectra of poly(dG-dC) . poly(dG-dC) in D2O solutions of high (4.0M NaCl) and low-salt (0.1M NaCl) exhibit differences due to different nucleotide conformations and secondary structures of Z and B-DNA. Characteristic carbonyl modes in the 1600-1700 cm-1 region also reflect differences in base pair hydrogen bonding of the respective GC complexes. Comparison with A-DNA confirms the uniqueness of C = O stretching frequencies in each of the three DNA secondary structures. Most useful for qualitative identification of B, Z and A-DNA structures are the intense Raman lines of the phosphodiester backbone in the 750-850 cm-1 region. A conformation-sensitive guanine mode, which yields Raman lines near 682, 668, or 625 cm-1 in B (C2'-endo, anti), A (C3'-endo, anti) or Z (C3'-endo, syn) structures, respectively, is the most useful for quantitative analysis. In D2O, the guanine line of Z-DNA is shifted to 615 cm-1, permitting its detection even in the presence of proteins.

Normal‐coordinate analysis of β‐carotene isomers and assignments of the Raman and infrared bands

Abstract: Normal-coordinate calculations were performed for the all-trans, 7-cis, 9-cis, 13-cis, 15-cis, 9, 13-di-cis, 9,13′-di-cis, 9,15-di-cis and 13,15-di-cis isomers of β-carotene The Raman and infrared bands of the all-trans and 15-cis isomers in the solid state were assigned on the basis of the results of the normal-coordinate calculations The Raman excitation profiles of the main Raman bands of the above two isomers in cyclohexane solution reported previously were satisfactorily correlated with the calculated vibrational modes and the molecular structures in the excited electronic states The Raman bands of the 7-cis, 9-cis, 13-cis, 9,13-di-cis, 9,13′-di-cis, 9,15-di-cis and 13,15-di-cis isomers were assigned The vibrational modes assigned to the Raman bands characteristic of the cis isomers were analysed in detail

Vibrational spectroscopy of mixed stack organic semiconductors: Neutral and ionic phases of tetrathiafulvalene–chloranil (TTF–CA) charge transfer complex

Abstract: The infrared and Raman spectra for the room temperature, quasineutral, and the low temperature, quasi‐ionic, phases of the mixed stack charge transfer complex tetrathiafulvalene–chloranil (TTF–CA) are reported. The analysis of the analogous data for a newly synthesized room temperature phase point to a dimerized segregated stack structure. All the vibrational data are interpreted and exploited through a clear identification of the differences, for the two types of stacks, in the spectroscopic effects due to the vibronic interaction, i.e., the coupling between electron and molecular vibration (e‐mv). It is shown that for distorted mixed stack complexes both Raman and infrared spectra can be substantially influenced by the vibronic interaction, whereas the dimerized segregated stack complexes, as already known, display striking vibronic effects only in infrared. The theoretical model which explains the origin of these effects is briefly summarized and its extension to mixed stack structures successfully use...

Determination of the charge carrier concentration and mobility in n-gap by Raman spectroscopy

Abstract: A method is presented which allows the determination of the charge carrier concentration and mobility in n-GaP by Raman spectroscopy of coupled plasmon-phonon modes. The results are compared with those of electrical measurements.

Atmospheric temperature measurements using a pure rotational Raman lidar

Abstract: A Raman lidar technique for measuring atmospheric temperature using pure rotational Raman spectra of N2 and O2 is discussed in detail. The use of a double-grating monochromator in the lidar for isolating two portions of the pure rotational Raman spectrum (PRRS) of N2 and O2 and suppressing the line of aerosol light scattering is experimentally shown to be very efficient. The feasibility of the method is convincingly illustrated by the results of laboratory experiments, as well as with measurements of air temperature carried out in the atmosphere. The accuracy of temperature measurements using the ratio of intensities of two portions of PRRS of N2 and O2 was ∼±0.74 K in laboratory experiments. The accuracy of the atmospheric temperature profile measurements using the lidar varied from 0.8 K at altitudes up to 300–400 mto, and slightly exceeded, ±1.5 K at 1-km height. Lidar temperature data are in good agreement with radiosonde data.

Low‐frequency Raman spectrum of supercooled water

Abstract: We report measurements of the Raman spectrum of supercooled water in the hindered translational region (20–400 cm−1) down to a temperature of −20 °C. The spectra are analyzed after correcting for the effects of Boltzmann factor and harmonic oscillator coupling, i.e., in the reduced R(ν) representation of Shuker and Gammon. Spectral deconvolution shows that in addition to the previously observed 0‐0‐0 bending mode (≂60 cm−1) and the 0‐0 stretching mode (≂190 cm−1), there is a weak feature at 260 cm−1 whose intensity increases by almost an order of magnitude as temperature decreases from 40 to −20 °C. A plausible interpretation of the 260 cm−1 band is that it is analogous to the 310 cm−1 band seen in ice I and probably arises because of differing electrostatic interactions in different configurations of coupled H bonds of neighboring H2O molecules. The 0‐0 stretching band at 190 cm−1 changes in many respects as temperature decreases from 40 to −20 °C: (i) Its peak intensity increases almost four times; (ii...

Resonance Raman excitation profiles of bacteriorhodopsin

Abstract: We have measured resonance Raman excitation profiles for 12 vibrational modes of light‐adapted bacteriorhodopsin using 27 excitation wavelengths ranging from 472 to 752 nm. The excitation profiles are quite similar and have approximately the shape and width of the absorption spectrum. Calculations using a 29‐mode harmonic sum over states with large amounts of inhomogeneous broadening (Gaussian standard deviation 750 cm−1) yield good fits to the absorption and excitation profile band shapes and to the absolute absorption and Raman cross sections. These calculations also give nearly correct intensities for most of the observed overtone and combination bands. The absolute Raman cross sections allow us to differentiate between the homogeneous and inhomogeneous contributions to the spectral breadth. Our upper limit of 250 cm−1 for the homogeneous linewidth, as well as the absence of strong low‐frequency Raman lines, implies that the lack of resolution in the bacteriorhodopsin absorption is due primarily to inh...