R-3 Repository :: Browsing by Author "Estle, Thomas L."

Browsing by Author "Estle, Thomas L."

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A computer controlled, narrow linewidth, broadly tunable, continuous wave laser
(1979) Ketkar, Suhas Narayan; Dunning, F. Barry; Tittel, Frank K.; Estle, Thomas L.
A continuous wave, tunable, single frequency dye ring laser has been developed. This laser is capable of giving output powers, in a single longitudinal mode, in excess of 7 mV, using different dyes and Second Harmonic Generation or Sum Frequency Mixing schemes, a wavelength coverage from 26 nm to 8 nm can be achieved. Using a PDP 11/3 minicomputer and a CAMAC dataway, control of a linear as well as a ring laser, oscillating in a single longitudinal mode, has been accomplished. The various optical elements in the dye laser cavity and the nonlinear mixing device are synchronously tracked. The laser can be operated both as a low resolution (4 GHz bandwidth) and a high resolution (.1 GHz bandwidth) visible and ultraviolet radiation source. Using Boyd and Kleinman theory for Second Harmonic Generation of focussed Gaussian beams,theoretical estimates for the wavelength and angle bandwidths are made. Some of the results have been experimentally verified.
Activity coefficient prediction by hard sphere expansion corresponding states theory
(1985) Quock, Deborah Eileen Reeder; Estle, Thomas L.; Miller, Clarence A.; Robert, Mark A.
A new method has been developed for predicting liquid activity coefficients in ternary mixtures from group contributions. In this method, activity coefficients are obtained by applying the Gibbs-Duhem equation to the excess Gibbs free energy of mixing. Gibbs free energies of the mixture and pure component fluids are calculated from an expansion about a reference fluid in powers of ratios of hard sphere diameters and molecular potentials. When the pure component differs from the reference by one additional structural group, these ratios represent the size contribution and the attraction contribution respectively of this group to the thermodynamic property of the pure fluid. Deviations of the reference hard sphere property to that of the fluid being modeled are corrected for by use of hard sphere equations of state. Results indicate that this method is useful for predieting activity coefficients of ternary mixtures from binary activity coefficient data.
An investigation by electron paramagnetic resonance of the Jahn-Teller effect in alkali-halides doped with transition group impurities nd_ configurations in six-fold coordination
(1972) Barksdale, Arlen O'Neil; Estle, Thomas L.
The EPR spectra of x-irradiated alkali-chloride single crystals doped with transition group impurities have been observed near 77°K at x-band frequencies. The optical spectra have been taken at room temperature. Samples of NaCl:Ag, NaCl:Cu, KC1:Ag, and KC1:Cu obtained from both Harshaw Chemical Company and lsomet were studied. Modifications to and operation of the existing back reflection homodyne EPR spectrometer of 1011AH spins sensitivity is described. An nd9 configuration such as Cu2+ or Ag2+ in the sixfold coordinated site of the alkali-chloride lattice has a doubly degenerate vibronic ground state as a result of lattice vibrational coupling to the electronic state. An effective Hamiltonian for this doublet vibronic ground state of the divalent impurities is formulated including the strain, Zeeman, and hyperfine interactions. An extension of the doublet formalism to include the effects of a nearby excited singlet vibronic state is discussed. No EPR spectra were observed in as-grown samples. After annealing at 500°C and x-irradiation at 77°K, two distinct types of spectra were observed at 77°K. One, observed only in KC1, is a pair of hyperfine lines separated by several hun-dred gauss, exhibiting ligand hyperfine structure, and attrib-utable to Ag°. The other, observed in both NaC1 and KC1, is a highly anisotropic pattern of several lines varying in intensity - the well-known Vk center resonance. Annealing to room temperature for the few minutes necessary for the Vk center fluorescence to die out and subsequent quenching to 77°K did not noticeably affect the neutral spectrum. However, the Vk center spectrum had almost completely vanished and in its place appeared a new axially symmetric spectrum from either a Cu2+ or a Ag2+ center. The divalent silver spectrum exhibited 13 hyperfine and ligand hyperfine lines in the perpendicular component and 2 hyperfine lines in the parallel component along a <100> axis in NaC1 and KC1. Along the same axis in NaC1 only, the EPR spectrum of the divalent copper displayed a broad resonance with some barely resolvable structure in the perpendicular component and a four line hyperfine pattern in the parallel component. The axial spectrum was not observed in KC1:Cu subsequent to x-irradiation and Vk-center anneal. This failure is attributed to an insufficient concentration of the monovalent copper impurity ions in substitional sites. All features of the observed axial spectra are explained within experimental error assuming the paramagnetic complex to be in the 2Eg ground state of the divalent transition group impurity ion in cubic symmetry. A static Jahn-Teller effect resulting from strong vibronic coupling can explain all of these observations.
An investigation by electron paramagnetic resonance of the Jahn-Teller effect in LiNbO₃¿:Cu²+
(1974) Setser, George Gordon; Estle, Thomas L.
EPR spectra for copper doped single crystals of LiNbO have been studied at temperatures from 1.3K to 133K. Copper, a 3d ion configuration, substitutes for one of the cations (site symmetry of C3) as Cu+. As a result of coupling to lattice vibrations, the ground manifold consists of a doubly degenerate vibronic ground state and a nearby singlet. An affective Hamiltonian that Includes the strain, Zeeman, and hyperflne interactions is formulated for ground manifolds of* l) doubly degenerate ground state, 2) doubly degenerate ground state with a singlet nearby, and 3) an accidentally degenerate triplet composed of a doublet and singlet. Further, an effective Hamiltonian (call it Hamiltonian number 4) for defect association is also formulated. The eigenvalue problems for these four effective Hamiltonians are solved using perturbation techniques and their predictions are compared to the EPR spectra. Because of the observed line intensities the spectra appears to fit most closely case 2), the so-called intermediate JahnTeller effect. High frequency EPR spectra must be obtained before Hamiltonians 3) and 4) can be entirely rulled out. Particular attention is given to the theoretical predictions of Hamiltonian 1) (the dynamic Jahn-Teller effective Hamiltonian) in which new spectral possibilities are presented. These new anisotropy features are shown to be a generalization of previous analyses.
Electric-field-effect and low temperature EPR studies of BaF₂¿:Mn++ and SrF₂¿:Mn++ crystals
(1978) Hoffman, John Russell; Estle, Thomas L.
Substituted Mn centers were studied in BaF2 and SrF2 crystals for possible off-center character. The angular dependence of the EPR spectra on the magnetic field direction was obtained at 1.3K and 4.2K in {11} crystal planes. Static electric fields up to 9 kV/cm were also applied along <111> and <1> at 4.2K and along <111> at 77K while taking EPR spectra. The EPR of SrF2:Mn++ was studied with similar electric fields along <111> directions at 4.2K. The splitting of EPR lines of a ruby crystal under an applied electric field demonstrated the experimental set-up functioned adequately. All spectra obtained for BaF2:Mn++ and SrF2:Mn++ showed no fine structure and were isotropic. The Mn appears to not be offcenter, but to have octahedral (h) site symmetry in these crystals.
Electron spin polarization in low energy diffraction from Ni(001) and Ni(001)c (2x2) Te
(1982) Jamison, Keith Douglas; Walters, G. King; Dunning, F. Barry; Estle, Thomas L.
Combined measurements in low-energy electron diffraction of both intensity and electron spin polarization are described for Ni(1) and Ni(1)c(2x2)Te. Polarizations and intensities are determined in the energy ranges 2-1V and 25 to 2V, respectively. The beam has been measured at angles of incidence in the range 1° to 18° for azimuthal angles $ = ° and § = 45°. The 1/2 1/2 and 1 beams have been studied at normal incidence. Significant polarizations are observed, even for the low atomic number crystal Ni (1). Pronounced changes in the polarization profiles are induced by the addition of a tellurium overlayer.
Investigations into the feasibility of EXAFS measurements on the local lattice structure near isolated impurities in crystals
(1979) Vanderwater, David A.; Estle, Thomas L.
In an effort to determine the feasibility of performing EXAFS measurements on the local environment of point defects in crystals, the spectra of several substitutional mixed alkali halide crystals was simulated by computer. These samples were chosen as preliminary systems that could be expected to give simple results. The results of these simulations, together with estimations of the magnitude of the background signal that would be present in any EXAFS measurement on impurities, indicates that with existing technologies even these preliminary samples could only give marginally acceptable results. For this reason the actual experiment was not attempted.
Laser induced refractive index changes in lithium niobate doped with cobalt
(1974) Ang, Dick; Estle, Thomas L.
The optical spectra of lithium niobate doped with cobalt were observed at room temperature and 77K. The absorption bands were identified using a theoretical energy level diagram. EPR spectra were obtained at 9 GHz and 4.2K. The observed spectra were explained with an axial spin Hamiltonian with an effective spin of 1/2. Holographic techniques were used to measure the laser-induced refractive index change at 514.5 and 488. nm. The holographic equipment and its operation are described in some detail.
Low frequency double electron Muon resonance in fused quartz
(1983) Warren, Mial E.; Estle, Thomas L.; Baker, Stephen D.; Dodds, Stanley A.
Double Electron Muon Resonance (DEMUR) is a double resonance technique for the study of muonium defect centers in insulators and semiconductors. A DEMUR experiment was performed at a low rf frequency to investigate the response of the muonium coupled spin system to perpendicular static and oscillating fields of comparable magnitude. The experiment was performed in fused quartz with a linearly polarized rf field resonant with the .dm =1 transition of the muonium triplet in a five gauss static field. For small rf field amplitudes, the results were as predicted by a theory consistent with the rotating wave approximation. For rf fields comparable in magnitude to the static field, significant deviations from the theory were observed. A theory for DEMUR with large alternating fields has not been developed.
Mixed P and N type conduction in RF sputtered Hg1-xCdXTe thin films
(1983) Liou, Tain-I; Wilson, William L.; Estle, Thomas L.; Brotzen, Franz R.
RF sputtered HgjCdTe thin films were deposited on <111> silicon substrates. Different values of negative bias were applied to the film during growth. X-ray diffraction was used to investigate the crystal structure of the films. Van Der Pauw and Hall measurements were used respectively to obtain resistivities and carrier concentrations of films at room temperature (3°K). Carrier concentration variation with temperature was also measured. A series of films were deposited with different substrate temperatures in order to investigate the effect on crystal structure and electrical properties. When substrate bias was increased, it was found that the film thickness decreased» the crystallographic order of the films became worse, and the room temperature resistivity increased. Measurement of carrier concentration versus temperature between 77°K and 3°K showed the films to be p type when the temperature was around 77°E and n type at high temperatures. It was also found that when the substrate temperature was increased during deposition, the crystal structure improved somewhat. Room temperature resistivity decreased, and the carrier type gradually changed from n type to p type as the deposition temperature was increased. A theoretical model using both a non-degenerate approximation as well as taking into account degenerate considerations was developed to compare with the experimental data.
NMR measurement of diffusion in liquids by the pulsed field gradient technique
(1983) Egan, Thomas F.; Rorschach, Harold E.; Hannon, James P.; Estle, Thomas L.
The diffusion coefficient is an important parameter for characterizing the state of water in biological systems. A nuclear magnetic resonance method of diffusion measurement by the pulsed field gradient, technique is described. A 9-T-18 spin-echo sequence is used with one gradient pulse located on each side of the 18 rf pulse. Information on restricted diffusion is obtained by varying the measuring time, which is determined by the separation of the gradient pulse pair. Measuring times greater than 2 msec are possible with the present apparatus. Maximum magnetic field gradients of 11 gauss/cm are applied to cylindrical sample volumes of 1 cm diameter and .5 cm in height. This permits the measurement of diffusion coefficients as low as 1 cm /sec. Details of the electronic hardware and gradient coil construction and calibration are given. The measurement process is software supported and includes digital data acquisition.
Paraelectric resonance of Li doped KC1 single crystals
(1969) Timme, Robert William; Estle, Thomas L.
Lithium ion impurities in potassium chloride form paraelectric defects which are crystal imperfections having a permanent electric dipole moment that can exist in one of several equivalent but geometrically different positions. The exact form of the defect is not yet known although experimental and theoretical work indicates the defect can tunnel from one equilibrium position to another thus leading to transitions between the resultant states. The process of stimulating electric dipole transitions between the energy levels is known as paraelectric resonance. Paraelectric resonance is the electrical analog to paramagnetic resonance. A microwave spectrometer with related equipment capable of observing paraelectric resonance has been designed and built and is described herein. Paraelectric resonance was observed at 29.1 GHz and at 1.3° K in KC1:Li+ samples for eight different electric field orientations. Transitions were observed for the following values of electric field. [see PDF for chart] Data was also obtained on the transition line widths and power saturation. Observations were made on KCl samples which had been melt doped with lithium and on samples which had been doped by diffusion. The transitions observed are not in good agreement with the simple tunneling models which neglect internal strains. More than the predicted number of lines appear for certain orientations of the electric field and fewer than the predicted number of lines appear for other orientations.
Paramagnetic resonance of transition group ions in crystals with the fluorite structure
(1970) Shen, Lewis Nai-Sing; Estle, Thomas L.
The electronic paramagnetic resonance of Co2+ in cubic sites of CaF2 and in trigonal sites of CdF2 have been observed at a frequency of 9 GHz and at liquid helium temperature. The trigonal spectra have an axial symmetry about a (lll) direction with g11 = 2.25 +/- 0.05 and g1 = 4.45 +/- 0.10. The origin of this trigonal center is unknown. The isotropic spectra can be described by a spin Hamiltonian with g = 2.32 +/- 0.01, u=-0.Oil +/- 0.004, A = 27.5 +/- 1.2 x lO-4 cm-1 and U = 3.5 +/- 3.5 x 10-4cm-1. The superhyperfine splitting parameters are estimated to be Af = 2.85 x 10-4cm-1 and Bf = 5.97 x lO-4cm-1. Heat treatment of the doped Ca?2 sample makes the cubic spectra diminish. This phenomenon is explained by a change in the valence' state of the paramagnetic ion. X-ray irradiation of the CaF2 sample doped with Co by diffusion changes the sample to red, but no Co^ + ions are observed. Attempts to convert the cubic spectra to trigonal ones by oxidation and hydrolysis do not yield any result.
Quasielastic neutron scattering study of water in agarose gels
(1980) Trantham, Eugene Clark; Rorschach, Harold E.; Estle, Thomas L.; Trammell, George T.
The differential cross section for the scattering of thermal neutrons from a solid or liquid contains information about the thermal motion of the nuclei. Measurement of the line shape in liquids for small energy transfer can be interpreted in terms of the mechanism of the diffusive motion and is refered to as the Quasielastic Neutron Scattering (QNS) technique. QNS has been used in this investigation to study the effect of macromolecules on the physical properties of water. A pilot study on the aqueous agarose gel system which made use of a triple axis spectrometer at the Oak Ridge National Laboratory has been completed. Studies have been conducted on the scattering intensity vs. energy transfer as a function of gel concentration and momentum transfer. The concentration dependence was studied by preparing gels of 4%, 9%, 15%, and 2% agarose by weight in H2O. The momentum transfer was studied for values of the scattered wave vector in the range .7A^-1 to 1.9A^-1. The contribution of the agarose to the scattering was determined by measuring the quasielastic spectrum of a 2% agarose in D2O gel. This allowed the scattering contribution of the water to be separated from that of the agarose. These data were analysed using the "bound-free" model for the distribution of correlation times in water. In this model, one fraction is assumed to be identical to pure water and the remaining fraction is assumed to be tightly bound to the agarose macromolecules. This analysis gave an estimate for the "bound" fraction in the 2% HgO gel of 21% +/- 4%. This result is in good agreement with previous nuclear magnetic resonance studies of the diffusion coefficient in agarose gels.
Studies of vibronic effects on the electron paramagnetic resonance of orbital triplets: transition metal ions in alkaline earth halides
(1977) Prater, Rudy Lester; Estle, Thomas L.
The effects of vibronic coupling on the electron paramagnetic resonance of transition metal ions that have orbital triplet ground states in alkaline earth halides have been investigated. Spectra have been obtained for two impurity ions, Cr2+ and Cr3+. The Cr2+ ion in CdPg and CaFg occupies a site that has axial symmetry along (lio) axes of the crystal. The Spin Hamiltonian for this ion which has a spin of two in the ground vibronic state is derived and a preliminary determination of some of the Spin Hamiltonian parameters has been made. According to currently held theoretical ideas, these data can be interpreted as a Static Jahn-Teller Effect in which the electronic triplet state couples to a vibrational doublet state and a vibrational triplet state with comparable coupling strengths. The Cr3+ ion in CaFg bas also been studied. It occupies a site that has axial symmetry along (ill) axes of the crystal. This behavior is predicted from a Static Jahn-Teller Effect in which the triplet electronic state couples predominantly to a triply degenerate vibrational mode. The Cr3+ ion has a spin of (3/2) in the ground vibronic state and the Spin Hamiltonian for this ion is derived. The temperature dependence of the data is used to give a rough estimate of the zero field splitting parameter, D, which agrees with the frequency dependence of the effective g-value.
Superconducting studies of large-scale structure in granular aluminum films
(1981) Harrington, Scott Nelson; Dodds, Stanley A.; Estle, Thomas L.; Hannon, James P.
Critical field measurements have been performed on granular aluminum films with normal state resistivities ranging from 9x1^-3 Q-cm to 6x1^-5 Q-cm. These experiments indicate the presence of thin internal layers within the films. The layer thickness generally decreases as Pjj decreases, but there is no evidence of layering in the cleanest film. From the angular dependence of the critical field, it has been determined that the layers are essentially decoupled. The perpendicular critical field, H(T), has an anomalous upward curvature, which we are unable to explain. The fluctuation conductivity of the granular films was also measured. Using the layer thickness determined from critical field data, there is good agreement with the two-dimensional Aslamazov-Larkin theory for a moderately dirty film. There is also agreement with the magnitude at intermediate reduced temperatures in very dirty films, but a marked deviation from the theoretical prediction at high t is noted, possibly due to a continuous decoupling of grains within a layer. For the cleanest film, there is fair agreement with the theory if the Maki-Thompson term is included.
The diffusion of positive muons in palladium
(1982) Stein, Robert T.; Dodds, Stanley A.; Estle, Thomas L.; Rorschach, Harold E.
The diffusion of the isotopes of hydrogen in nonmagnetic metals has been of interest for many years. Muon spin rotation (uSR) has permitted the study of the diffusion of the positive muon as a light isotope of hydrogen. This experimental technique has been applied successfully to the diffusion of positive muons in palladium. Classical diffusion theory does not seem to explain the experimental results. A quantum mechanical calculation which explains the results has not yet been made.
The effects of applied stress on the E. P. R. spectra of a system exhibiting the dynamic Jahn-Teler effect: CaF₂¿:Sc²+
(1974) Mier-Maza, Rafael; Estle, Thomas L.
The effects of uniaxial stress applied along different crystallographic directions to a cubic system exhibiting the Dynamic Jahn-Teller effect have been studied. E.P.R. measurements were made at 9 Ghz at liquid helium temperatures. Experimental data were obtained as a function of the orientation of the magnetic field and the magnitude and direction of the stress. The observed spectra can be explained by the effective Hamiltonian formulation of Ham and extended by Herrington, Estle and Boatner. The effective Hamiltonian has been further extended to account for the superhyperfine (S. H. F.) interaction with the eight nearest fluorines. Good resolution has been obtained for the S. H. F. interaction in the large stress limit and a method for the determination of the S. H. F, parameters has been proposed.
The hindered rotation of orbitally-singlet diatomic molecules in ionic crystals
(1982) Das, Pulak Kumar; Estle, Thomas L.; Trammell, George T.; Kilpatrick, John E.
The hindered rotation of orbitally—singlet diatomic molecules in ionic crystals at sites of symmetry has been studied using the Hindered Rotor model. The static crystalline field due to the crystal is expanded in terms of spherical harmonics and symmetrized to transform like the totally symmetric representation of the group. The rotational wave functions are also expanded in terms of spherical harmonics up to about t = 2 and symmetrized to transform like any one of the ten irreducible representations of the ^ group. The eigenvalues are calculated in terms of the molecular moment of inertia for various values of the parameters characterizing the hindering potential.
The measurement of the diffusion coefficient of water in poly (ethylene oxide) water solutions using a nuclear magnetic resonance pulsed field gradient technique
(1983) Bearden, Daniel W.; Rorschach, Harold E.; Estle, Thomas L.; Huang, Huey W.
Nuclear magnetic resonance (NMR) techniques have often been used in studies of the interaction of water molecules with complex macromolecular structures such as proteins and polymers. We have measured the diffusion coefficient of protons in water/poly (ethylene oxide) solutions as a function of concentration using a pulsed field gradient NMR technique, for values of the concentration of poly-ox in H2O from to 1.2 gm poly-ox/gm. Near zero poly-ox concentration, the slope of the D vs. concentration curve is quite large. As the concentration increases, the slope decreases, and at 1.2 gm poly-ox/gm H2O the diffusion coefficient is reduced by a factor of about 6 from the value at zero concentration. This paper presents the theory of field gradient methods used to measure diffusion coefficients, describes the apparatus and technique used for our measurements, and attempts to interpret the measured diffusion coefficients by considering a two phase model which treats obstruction and hydration effects in a unified way.

Browsing by Author "Estle, Thomas L."

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