Showing papers on "Relaxation (NMR) published in 1986"
TL;DR: The theory of plasma relaxation is described and developed in this article, which involves reconnection of magnetic field lines in a manner that destroys all the topological invariants of ideal plasma so that only total magnetic helicity survives.
Abstract: The theory of plasma relaxation is described and developed. Turbulence, allied with a small resistivity, allows the plasma rapid access to a particular minimum-energy state. This process involves reconnection of magnetic field lines in a manner that destroys all the topological invariants of ideal plasma so that only total magnetic helicity survives. Although this mechanism, and the equations describing the relaxed state, are similar in all systems, the properties of the relaxed state depend crucially on the topology---toroidal or spherical---of the container and on the boundary conditions. Consequently there are several different types of relaxed state, each with its own special characteristics, which are derived and discussed. The measurements made on many experiments, including toroidal pinches, OHTE, multipinch, and spheromaks, are reviewed and shown to be in striking agreement with the theoretical predictions.
1,216 citations
Book•
24 Apr 1986
TL;DR: In this article, the authors present a model of structural relaxation in OXIDE GLASSES, including the Sandwich Seal and the Composite Cylinder, as well as the split ring composite.
Abstract: VISCOELASTICITY IN OXIDE GLASSES. The Glass Transition. Elasticity and Viscoelasticity. Linear Viscoelastic Behavior in Oxides. Experimental Studies of Relaxation and Creep. Thermorheological Simplicity. Unstabilized Glass. The Visoelastic Analogy. The Sandwich Seal. STRUCTURAL RELAXATION Fictive Temperature. Phenomenological Model of Structural Relaxation Time. Universality of Glass Transition Phenomena. RELAXATION IN COMPOSITES. Relaxation in the Sandwich Seal. Composite Cylinder. Composite Sphere. Split Ring Composite. Interrelating Setting Temperatures. Elastic-Clad Composites. Glass-to-Glass Composites. Approximate Methods of Viscoelastic Analysis. Appendixes. Index.
649 citations
TL;DR: By reducing the electromagnetic field fluctuations in one quadrature phase, squeezed light can inhibit the phase decay of an atom by giving three relaxation times, which are inversely proportional to the variances of the two quadratures phases of the incident light.
Abstract: It is shown that by reducing the electromagnetic field fluctuations in one quadrature phase, squeezed light can inhibit the phase decay of an atom. The effect is to give three relaxation times; the usual longitudinal relaxation time, and two different transverse relaxation times, which are inversely proportional to the variances of the two quadrature phases of the incident light.
409 citations
TL;DR: Three theories based on different physical mechanisms, the direct-transfer model, the hierarchically constrained dynamics model, and the defect-diffusion model are shown to have an underlying common mathematical structure.
Abstract: Empirical evidence has accumulated showing the wide occurrence of a stretched-exponential relaxation decay law for many diverse condensed-matter systems. Several theories based on different physical mechanisms have been successful in deriving the stretched-exponential decay law in a natural way. Three of these theories, the direct-transfer model, the hierarchically constrained dynamics model, and the defect-diffusion model are shown here to have an underlying common mathematical structure.
347 citations
TL;DR: In this article, the authors presented a method of analyzing relaxation decay curves in terms of continuous distributions of relaxation times, rather than depending on a priori assumptions, the experimental data determine the number and character of the components.
213 citations
TL;DR: In this article, a review of recent developments in the expanding phenomenology of amorphous solid electrolytes is presented, and the authors emphasize the importance of studying the fast ion motions by mechanical response, in addition to electrical response measurements.
185 citations
TL;DR: In this article, the authors considered the case that the motion of the system is on a single potential energy surface and the case where this motion occurred on two surfaces was considered elsewhere.
Abstract: Intramolecular charge transfer are considered for the case that the motion of the system is on a single potential energy surface. The case where this motion occurred on two surfaces was considered elsewhere. The former is shown to be much preferable for studies of solvent dynamics. Several aspects of the relation between ‘‘constant charge’’ dielectric relaxation time of the polar solvent and the experimental decay time of emission from the polar excited state of the solute are discussed for hydrogen‐bonded systems.
183 citations
TL;DR: The water relaxation ability of ferromagnetic, albumin‐coated magnetite (Fe3O4) particles has been investigated and these particles are quite effective at reducing both T1 and T2 at relatively low particle concentrations.
Abstract: Most contrast agents used in NMR imaging studies to date have been paramagnetic. However, it is also possible to obtain selective contrast with a ferromagnetic agent, and these agents are potentially more sensitive than paramagnetic compounds because of their large magnetic moments. The water relaxation ability of ferromagnetic, albumin-coated magnetite (Fe3O4) particles has been investigated. These particles are quite effective at reducing both T1 and T2 at relatively low particle concentrations. The potential applications of these particles include improved visualization of the liver, gastrointestinal tract, and genitourinary tract, as well as specific targeting and detection of small tumors or other cells with unique surface receptors. © 1986 Academic Press, Inc.
164 citations
TL;DR: In this article, the 584 A photoelectron spectra of supersonic molecular beams of H2O and D2O have been obtained with improved resolution, and autocorrelation functions were calculated from the photo-electron bands of all three electronic states.
Abstract: The 584 A photoelectron spectra of supersonic molecular beams of H2O and D2O have been obtained with improved resolution. The spectroscopic constants of the X 2B1 and A 2A1 state ions, including ω01, x011, ω02, x022, and x012, are reported. For the first two electronic states of the ion, precise line splittings were evaluated with a least squares fitting procedure, employing sums of empirical instrument response functions and a linear background. A simulation of the vibrational manifolds of the B 2B2 state ions with combination progressions in the symmetry‐allowed modes ν1 and ν2 failed to reproduce the diffuse photoelectron bands observed for both H2O and D2O. Autocorrelation functions were calculated from the photoelectron bands of all three electronic states. The B 2B2 state correlation functions exhibit ultrafast decay, occurring on a 10−14 s time scale. The ν2 motion appears to define the decay in the correlation function. This behavior supports a previously proposed B 2B2–A 2A1 curve‐crossing model for the nonradiative relaxation of the B 2B2 state ions.
144 citations
TL;DR: In this paper, electrical conductivity and relaxation studies have been carried out on Parel 58 elastomer with a variety of lithium salts in vacuum over the temperature range 5-380 K and at pressures up to 0.65 GPa.
Abstract: Audio frequency electrical conductivity and relaxation studies have been carried out on Parel 58 elastomer and Parel 58 elastomer complexed with a variety of lithium salts. The measurements have been carried out in vacuum over the temperature range 5–380 K and at pressures up to 0.65 GPa over the temperature range 230–380 K. Both the electrical conductivity for the complexed material and the electrical relaxation time associated with the α relaxation in the uncomplexed material exhibit VTF or WLF behavior. From a VTF analysis for both the vacuum electrical relaxation time and electrical conductivity, Ea is found to be about 0.09 eV and T0 is found to be about 40 °C below the ‘‘central’’ glass transition temperature. In addition, it is found that the activation volumes for the electrical relaxation time and the electrical conductivity are the same when compared relative to T0. These results imply that the mechanism controlling ionic conductivity is the same as that for the α relaxation, namely large‐scale segmental motions of the polymer chain.
117 citations
TL;DR: In this article, the frequency and temperature dependence of the elastic moduli of commercially available polymers has been studied in the temperature range of 0-35°C and for frequencies 102-106 Hz.
Abstract: The frequency and temperature dependence of the elastic moduli of a number of commercially available polymers has been studied in the temperature range of 0–35 °C and for frequencies 102–106 Hz. Away from transitions a significant new relationship has been obtained, i.e., the Young’s modulus of these polymers is proportional to log of frequency. Using this relationship, together with the low and high frequency data, transitions in some of the polymers were identified.
TL;DR: In this article, a density matrix formalism based on the stochastic Liouville equation is employed to study molecular order and dynamics of deuteron (2H) labeled phospholipid membranes.
Abstract: Multipulse dynamic NMR has been employed to study molecular order and dynamics of deuteron (2H) labeled phospholipid membranes. Variation of pulse sequence and pulse separation provides the large number of independent experiments necessary for a proper molecular characterization of the systems. Analysis of these experiments is achieved by employing a density matrix formalism, based on the stochastic Liouville equation. Arbitrary relaxation rates and line shapes of single and multiple quantum transitions are considered.The various 2H NMR experiments of macroscopically unoriented bilayers of 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphocholine (DMPC), specifically deuterated at the 6‐ and 14‐position of the 2‐chain, are faithfully reproduced by the model. Computer simulations provide the orientational distributions and conformations of the hydrocarbon chains and the correlation times of the various motions. In the Lα phase the correlation times τR∥ and τR⊥ for chain rotation and chain fluctuation are of the order of...
TL;DR: A detailed Monte Carlo study of the equilibrium and dynamical properties of the two-spin facilitated kinetic Ising model proposed by Fredrickson and Andersen (FA) is presented in this paper.
Abstract: A detailed Monte Carlo study of the equilibrium and dynamical properties of the two‐spin facilitated kinetic Ising model proposed by Fredrickson and Andersen (FA) is presented. The model Hamiltonian is that of a spin‐1/2 Ising model in an external magnetic field and, in the present study, contains no interactions between spins. The kinetic properties of the model are described by a master equation with single‐spin‐flip dynamics and highly cooperative flip rates. In particular, the rate at which a spin flips is chosen to be zero unless at least two of its neighbors are spin up. Monte Carlo simulations of the model on a square lattice demonstrate that although there is no evidence for a kinetic singularity (as predicted by FA), the model has dynamical properties much like those of viscous liquids. We find non‐Arrhenius temperature dependence of the average relaxation time and highly nonexponential decay of various relaxation functions. The expression derived by Adam and Gibbs is found to describe the relationship between the average relaxation time and the entropy of the spin model. It is shown that the equilibrium time correlation functions can be accurately fit to the Kohlrausch–Williams–Watts (KWW) expression. The exponent in the KWW function is found to decrease as the temperature is lowered. Studies of multiple‐spin correlation functions demonstrate how spatial correlations develop in the model as it is perturbed from equilibrium and how these relax as the system equilibrates.
TL;DR: In this article, the authors applied Narayanaswamy's model of structural relaxation to the data of Hara and Suetoshi on volume relaxation in plate glass and used both the Adam-Gibbs and Arrhenius equations to represent the relaxation time.
Abstract: Narayanaswamy's model of structural relaxation is applied to the data of Hara and Suetoshi on volume relaxation in plate glass. Both the Adam-Gibbs and Arrhenius equations are used to represent the relaxation time. Equally good fits are obtained with both equations, but only the Adam-Gibbs model gives Physically meaningful fitting parameters. The exponent b describing the shape of the relaxation time spectrum decreases at small values of reduced time, as it does for stress relaxation Discrepancies between calculated and measured densities at 350°C are not resolved by allowing for a nonlinear driving force or thermorheological complexity.
TL;DR: Comparisons of NMR relaxation times obtained by both in vivo and in vitro NMR spectroscopy of brain-tissue samples from young adult rats with cold lesions, fluid-percussion injury, hypoxic-ischemic injury, bacterial cerebritis, and cerebral tumor suggest that prolongation of T2 is a better indicator of increased water content than prolonging of T1.
Abstract: ✓ Many aspects of the use of high-resolution nuclear magnetic resonance (NMR) imaging in the examination of brain edema have not been fully explored. These include the quantitation of edema fluid, the ability to distinguish between various types of edema, and the extent to which tissue changes other than a change in water content can affect NMR relaxation times. The authors have compared NMR relaxation times obtained by both in vivo magnetic resonance imaging (MRI) and in vitro NMR spectroscopy of brain-tissue samples from young adult rats with cold lesions, fluid-percussion injury, hypoxic-ischemic injury, bacterial cerebritis, and cerebral tumor. Changes in relaxation times were compared with changes in brain water content, cerebral blood volume, and the results of histological examination. In general, both in vivo and in vitro longitudinal relaxation times (T1) and transverse relaxation times (T2) were prolonged in the injured hemispheres of all experimental groups. Water content of tissue from the inj...
TL;DR: Results suggest that water in contact with trabecular bone in vivo will exhibit shortened relaxation times, which could be explained by a surface interaction at the bone/liquid interface, which restricted rotational and translational motion of nearby molecules.
Abstract: Preliminary attempts by our group at UCSF to assess fat content of vertebral marrow in the lumbar spine using relaxation time information demonstrated that the presence of trabecular bone affects relaxation times. The objective of this work was a thorough study of the effects of bone on NMR relaxation characteristics of surrounding liquids. Trabecular bone from autopsy specimens was ground up and sifted into a series of powders with graded densities ranging from 0.3 gm/cc to 0.8 gm/cc. Each powder was placed first in n-saline and then in cottonseed oil. With spectroscopy, spin-lattice relaxation times (T1) and effective spin-spin relaxation times (T2*) were measured for each liquid in each bone powder. As bone density and surface to volume ratio increased, T1 decreased faster for saline than for oil. T2* decreased significantly for both water and oil as the surface to volume ratio increased. It was concluded that effects of water on T1 could be explained by a surface interaction at the bone/liquid interface, which restricted rotational and translational motion of nearby molecules. The T1s of oil were not affected since oil molecules are nonpolar, do not participate in significant intermolecular hydrogen bonding, and therefore would not be expected to interact strongly with the bone surface. Effects on T2* could be explained by local magnetic field inhomogeneities created by discontinuous magnetic susceptibility near the bone surface. These preliminary results suggest that water in contact with trabecular bone in vivo will exhibit shortened relaxation times.
TL;DR: In this paper, the energy relaxation time and dephasing time of a system of molecules interacting by spherically symmetric intermolecular and vibrational potentials have been evaluated by the molecular dynamics method.
Abstract: The energy relaxation time (T1) and dephasing time (T2) of a system of molecules interacting by spherically symmetric intermolecular and vibrational potentials have been evaluated by the molecular dynamics method The computational ease introduced by the spherical symmetry of the potentials allows an extensive study of the density variations of T1 and T2 from the gas phase to the highly compressed liquid and solid, as well as of the influence of a long range component in the vibrational potential on the relaxation times The general trends which proceed from this study are compared with recent theoretical approaches and experimental observations
TL;DR: In this paper, the frequency dependence and amplitude of the rotational spectral density function, J(omega), was determined for sucrose solutions in D/sub 2/O NMR spinlattice relaxation times and nuclear Overhauser enhancements.
Abstract: /sup 13/C NMR spin-lattice relaxation times and nuclear Overhauser enhancements were measured as a function of concentration, temperature, and magnetic field strength for sucrose solutions in D/sub 2/O. These data were used to determine the frequency dependence and amplitude of the rotational spectral density function, J(omega). The authors find that J(omega) has the same frequency dependence as the theoretical spectral density function for a rigid molecule, but it has a lower amplitude. At the average ring-carbon atom in sucrose, the low-frequency amplitude of J(omega) is about 89% of the theoretical rigid-molecule value. Presumably, the amplitude is lowered by rotational components of vibrational motions, which rapidly accomplish part of the averaging that otherwise would be performed by the slower molecular rotations of a rigid molecule. The results also reveal small differences in the amplitudes of J(omega) at different sucrose ring positions; these differences can be used to measure the relative amplitudes of local torsional and vibrational motions.
Book•
01 Dec 1986
TL;DR: Inverse Laplace transform of Kohlrausch relaxation function is used in this paper to model the reaction kinetics of species trapped in glassy matrices, where the authors show that the reactivity distribution of species in micelles is different with time-dependent rate constant.
Abstract: 1. Introduction.- 2. Reaction kinetics of species trapped in glassy matrices.- Excess electrons.- Post-irradiated decay.- Spectral relaxation.- Photostimulated decay.- Photostimulated conversion into trapped hydrogen atoms.- Radioluminescence kinetics.- Hydrogen atoms.- Kinetics of trap-limited decay.- Effect of irradiation temperature on decay rate.- Mechanism of decay.- Effect of matrix dynamics on decay patterns.- Alkyl radicals.- Decay patterns.- Applicability of ?t law.- Oxidation kinetics.- Some other species.- Disproportionation of Cl?2.- Recombination NO3 + NO2?2?2 N0?3.- Arylcarbenes decay.- 3. Kinetic behaviour of water radiolysis products in polycrystalline ice.- Trapped electrons.- Hydrogen atoms.- Hydroxyl radicals.- Structural relaxation in polycrystalline ice.- Some other polycrystalline systems.- 4. Decay of radicals in polymer matrices.- Allyl radicals in polyethylene.- Propagating radicals in poly(methyl methacrylate).- ITL of X-irradiated polystyrene.- 5. Lifetime distributions of photoproduced cation-radicals in micelles.- Time-dependent reactivity of species embedded in micelles.- Solvent isotope effect.- Effect of micellar interface modification on reactivity of embedded species.- Distribution of activation energy for decay of embedded species.- Kinetic behaviour of photoe jected electrons.- 6. Molecular origins of reactivity distribution in condensed media.- Time-dependent rate constant in CTRW model.- CTRW model of nonexponential relaxation.- Barrier dispersion model of waiting-time distribution function.- 7. Appendices.- A. Kinetics with time-dependent rate constant.- B. Inverse Laplace transform of Kohlrausch relaxation function.
TL;DR: In this paper, the mean magnetic field quasi-linearly, and for long-wavelength modes using the direct interaction approximation, is calculated for tearing mode turbulence, which accounts for current relaxation in reversed-field pinch experiments, and gives a magnetic fluctuation scaling of S to the -1/3.
Abstract: Tearing mode turbulence produces a hyperresistivity or effective anomalous electron viscosity. The hyperresistivity is calculated for the mean magnetic field quasi-linearly, and for long-wavelength modes using the direct interaction approximation. The hyperresistivity accounts for current relaxation in reversed-field pinch experiments, and gives a magnetic fluctuation scaling of S to the -1/3. It causes enhanced tearing mode growth rates in the turbulent phase of tokamak disruptions. In astrophysics, it limits magnetic energy growth because of the dynamo effect, and may explain rapid reconnection phenomena such as solar flares.
TL;DR: In this article, the effect of water content on the spinlattice relaxation time and bond-angle distribution of vitreous silica was investigated using 29Si magic-angle spinning nuclear magnetic resonance spectroscopy.
Abstract: A preliminary investigation, using 29Si magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), of the effect of water content on the spinlattice relaxation time, T 1, and Si[sbnd]O[sbnd]Si bond-angle distribution of vitreous silica is reported. The decrease in T 1 with increase in water content suggests that water acts as a major relaxation centre in vitreous silica and a change in water content is also seen to produce a subtle change in the NMR lineshape. The chemical shift of the 29Si resonance occurs at–111·5 p.p.m. with reference to tetramethylsilane (TMS) and the resulting Si[sbnd]O[sbnd]Si bond-angle distribution is seen to be asymmetric about a peak at 143· · 1· and is in agreement with the X-ray data of Mozzi and Warren (1969).
TL;DR: For an infinite liquid column consisting of various immiscible visco-elastic liquids exhibiting free surface and interface tension, the transcendental frequency equation is presented in this paper, where the natural damped frequencies depend on the viscosities, densities, surface and interfaces tension and upon the Maxwell relaxation times.
TL;DR: The overall frequency dependence of the spin-lattice relaxation time of backbone-coupled protons of proteins or polypeptides was found to be T1 ∼ ν0.74±0.06 over several decades, and this T1 dispersion also appears to be independent of the protein/polypeptide species.
TL;DR: In this paper, an alternate copolymer of vinylidene cyanide and vinyl acetate has been investigated dielectrically at temperatures above Tg ~170°C and a remarkable relaxation was observed in the 1 Hz to 10 kHz frequency range due to a separation from coexisting contributions.
Abstract: An alternate copolymer of vinylidene cyanide and vinyl acetate has been investigated dielectrically at temperatures above Tg ~170°C A remarkable relaxation was observed in the 1 Hz to 10 kHz frequency range due to a separation from coexisting contributions as a result of the dc conductivity The relaxation time depends upon the temperature in the WLF according to the characteristics of the micro-Brownian motions of molecular segments The relaxation strength was found to reach 125, resulting in an unusually high dielectric constant Such a large relaxation strength is an indication of some cooperative effects in relation to dipolar motions Cooling to below Tg in the presence of a high electric field creates a large remanent polarization which is consistent with the strong piezoelectric activity reported for this copolymer
TL;DR: In this article, a multiphase model involving three populations of water protons in rapid exchange was proposed to explain the time dependence of T2 after quenching in gelatin gels.
TL;DR: In this paper, a survey of high-resolution and broad-line NMR spectra of 57Fe, 59Co and '°3Rh nuclei in mono and dinuclear olefin complexes are discussed.
Abstract: Significant advances in NMR detection of insensitive, low-frequency spin-l/2 and quadrupolar nuclei have caused rapid progress in the application of transition metal NMR spectroscopy to organometallic chemistry. As a result, the structural dependence of metal NMR parameters, i.e. chemical shifts, heteronuclear and homonuclear spin coupling and relaxation times, has become a topical field of research. Following a survey of current detection methods, high-resolution and broad-line NMR spectra of 57Fe, 59Co and '°3Rh nuclei in monoand dinuclear olefin complexes are discussed. Particular attention is given to structural effects on nuclear shielding in low-valent metal complexes, to metal-carbon spin coupling, stereoelectronic effects in p,d-bonding, charge distribution in dinuclear complexes, and to intramolecular dynamic processes. For substituted CpCo(COD) and IndCo(COD) complexes quantitative correlations between 59Co shielding and the activity and regioselectivity in homogeneous catalysis of the pyridine synthesis permit a novel and effective screening of catalysts. The first report on 59Co-NMR spectra of cobalamins (vitaminB12 and methylcobalamin) suggests potential applications in biocatalysis. INTRODUCTION The thorough investigation of transition metal NMR spectroscopy of organometallic compounds was handicapped for a long time by a lack of sensitive detection techniques suitable to cover a wide range of resonance frequencies. During the past few years, the availability of high-field spectrometers, with provision for the use of large sample volumes in conjunction with broadbanded r.f. electronics and programmable pulse generators, has caused a real break-through in a field which may be considered of great potential for organometallic chemistry and homogeneous catalysis. METHODS Experimental problems for the detection and routine measurement of transition metal resonances may arise from either of the following facts. First, very small magnetic moments lead to low Larmor frequencies and sensitivities and, for spin-l/2 nuclei, to rather long spin-lattice relaxation times, e.g. 57Fe, '°3Rh, '°7Ag/'°9Ag. Second, nuclei with spin 1 may have large electric quadrupole moments (e.g. 59Co, 61Ni, '°5Pd) which cause extremely short nuclear relaxation times T1 and T2, the latter being responsible for large experimental line width (up to 30 KHz). In addition, low natural isotope abundance may lead to detection problems due to very small over-all receptivity. The magnetic properties of some typical transition metals of major chemical importance are summarized in Table 1. * Transition metal NMR spectroscopy Part VIII, Part VII: ref. 1.
TL;DR: In this article, the hypersonic speed of sound (C/sub h/) was measured in the tert-butyl alcohol-water system (TBA/water) from 0.0 to 0.16 mole fraction of TBA at 10-45 /sup 0/C by Brillouin scattering.
Abstract: The hypersonic speed of sound (C/sub h/) has been measured in the tert-butyl alcohol-water system (TBA/water) from 0.0 to 0.16 mole fraction of TBA at 10-45 /sup 0/C by Brillouin scattering. Considerable dispersion in the C/sub h/ as compared to that found in the zero frequency and ultrasonic range is observed. The isentropic compressibilities in the hypersonic range are also presented for 10, 20, and 25 /sup 0/C. Photon correlation spectroscopy (PCS) gave no evidence of the presence of oligimers in the system and depolarized interferometry measurements detected no rotational diffusion by species in the system. The acoustic relaxation times calculated at mole fraction of TBA equal to 0.105 were found to be in agreement with literature values of both NMR and dielectric relaxation measurements on this system. The results obtained were interpreted from the view point that the relaxation time observed was due to a structural relaxation. 46 references, 4 figures, 2 tables.
TL;DR: The data span over nine decades in frequency and obey a Vogel-Fulcher relaxation model over the temperature range 6-15 K with an extrapolated transition at 3.0 K to a glassy dipolar state.
Abstract: We have directly observed fluctuating dipolar clusters in the mixed crystal K${\mathrm{Ta}}_{0.991}$ ${\mathrm{Nb}}_{0.009}$${\mathrm{O}}_{3}$ using inelastic-light-scattering techniques for temperatures between 1.8 and 25 K and for electric fields up to 2 kV/cm. Together with earlier dielectric-relaxation data, our data span over nine decades in frequency and obey a Vogel-Fulcher relaxation model over the temperature range 6-15 K with an extrapolated transition at 3.0 K to a glassy dipolar state.
TL;DR: In this article, a new technique is described in which a transient thermoelectric (TTE) voltage of a semiconductor is measured after a pulsed laser irradiation, a modification of photodiffusion or Dember effect.
Abstract: A new technique is described in which a transient thermoelectric (TTE) voltage of a semiconductor is measured after a pulsed laser irradiation—a modification of photodiffusion or Dember effect. This technique has been successfully applied to test samples of n‐ and p‐Si over the wide time range from 20 ns to 2 s and the temperature 120–284 K. The decay curves of the TTE voltage consist of three stages with the characteristic relaxation or decay times. Stage 1 with the relaxation time τ1, is associated with the carrier generation and recombination and explained by the Dember effect. Stage 2 characterized by the relaxation time τ2, is due to the diffusion of majority carriers from a higher to a lower temperature region; for p‐Si, a double‐relaxation process is observed arising from the difference in the drift mobilities of light and heavy holes. At stage 3, the TTE voltage vanishes completely, which can be reasonably interpreted by the diffusion of thermal flux or phonons along a temperature gradient produced by the laser pulse. Analytical expressions for each stage are presented to discuss these experimental results.