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in subjects: "Nuclear Techniques In Condensed Matter Physics"

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Application of spin-sensitive electron spectroscopies to investigations of electronic and magnetic properties of solid surfaces and epitaxial systems. Progress report, 1 November 1992--31 October 1993

Research during this year focused on angular dependence of polarization of electrons backscattered from metallic surfaces, as a function of energy loss, using spin-polarized electron energy loss spectroscopy (SPEELS), and on dynamics of metastable He(2{sup 3}S) deexcitation at Xe-covered metallic surfaces using spin-polarized metastable deexcitation spectroscopy (SPMDS). In the SPEELS study, the data from Au, Ag, Mo, and Fe surfaces suggest that all inelastically scattered electrons underwent s… more

Date: April 1, 1993

Creator: Walters, G. K. & Dunning, F. B.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Spectroscopic imaging, diffraction, and holography with x-ray photoemission

X-ray probes are capable of determining the spatial structure of an atom in a specific chemical state, over length scales from about a micron all the way down to atomic resolution. Examples of these probes include photoemission microscopy, energy-dependent photoemission diffraction, photoelectron holography, and X-ray absorption microspectroscopy. Although the method of image formation, chemical-state sensitivity, and length scales can be very different, these X-ray techniques share a common go… more

Date: February 1, 1992

Item Type: Article

Partner: UNT Libraries Government Documents Department

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X-ray scattering studies of non-equilibrium ordering processes. Progress report, November 1, 1990--October 31, 1991

We report on the progress of the project entitled ``X-ray Scattering Studies of Non-Equilibrium Ordering Processes.`` The past year has seen continued progress in the study of kinetic effects in metallic binary alloys and polymers. In addition, work has begun on a low dimensional CDW system: blue bronze. A sample chamber has been constructed to perform small angle neutron scattering measurements on a model quantum system with phase separation: solid He3/He4. Work is continuing on magnetic syste… more

Date: December 31, 1991

Creator: Nagler, S. E.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Two dimensional NMR and NMR relaxation studies of coal structure. Progress report, October 1, 1993--December 31, 1993

Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups that determine the reactivity of coals. Special attention is being paid to methods that are compatible with the very high magic angle sample spinning rates needed for operation at the high magnetic field strengths available today. Polarization inversion methods utilizing the difference in heat capacities of small groups of spins… more

Date: December 31, 1993

Creator: Zilm, K. W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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X-ray and neutron scattering studies of magnetic critical fluctuations in holmium

We describe measurements of the magnetic critical fluctuations of holmium by x-ray scattering techniques. The x-ray results are compared to those obtained in neutron scattering experiments performed on the same sample.

Date: April 1, 1993

Creator: Thurston, T. R.; Helgesen, G.; Gibbs, D.; Shirane, G.; Hill, J. P. & Gaulin, B. D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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FEFF5: An ab initio multiple scattering XAFS code

FEFF5 is an efficient automated code which calculates multiple scattering (MS) curved wave XAFS spectra for molecules and solids. The theoretical ingredients and approximations contained in the code are revised, with the aim of describing the how XAFS spectra are efficiently simulated. The FEFF5 code consists of 4 independent modules: a scattering potential and phase shift module, a path finder module, a scattering amplitude module and an XAFS module. Multiple scattering Debye-Waller factors ar… more

Date: December 31, 1992

Creator: Rehr, J. J. & Zabinsky, S. I.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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A new matrix for the ``ageless`` 21.6-keV {sup 151}Eu nuclear gamma ray Moessbauer source

Moessbauer spectroscopy has been used over the past two decades to advance the study of europium compounds and alloys, primarily utilizing the 21.6-kev gamma ray emitted from beta decaying {sup 151}Sm. This isotope, which has a 87 year half-life, has been used in either a samarium fluoride (SmF{sup 3}) or samarium oxide (Sm{sub 2}O{sub 3}) matrix. We now report a study involving, europium oxalate decahydrate (Eu2(C{sub 2}O{sub 4}){center_dot}10H{sub 2}O), europium fluoride EuF{sub 3} and EuBe{s… more

Date: March 1, 1993

Creator: Wynter, C. I.; Haustein, P. E.; Stadelmaier, H.; Thorpe, A.; Spijkerman, J. J. & Nowik, I.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Neutron scatter studies of chromatin structure related to functions. Progress report, July 1, 1988--June 30, 1989

Neutron scatter studies have been performed at LANSCE, LANL and at the Institute Laue Langevin, Grenoble, France. In the previous progress report (April 1, 1988--July 1, 1988) the following objectives were listed: shape of the histone octamer; location of the N-terminal domains of histone in the nucleosome core particle (specific aim 1 of original grant proposal); effect of acetylation on nucleosome structure (specific aim 2); location of the globular domain of histone H1 (specific aim 6); and … more

Date: December 31, 1989

Creator: Bradbury, E. M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Magnetic resonance studies of photo-induced electron transfer reactions. Final report, June 1, 1990--May 31, 1993

Fourier Transform Electron Paramagnetic Resonance (FT EPR) is useful in study of photochemical reactions: a microwave pulse rotates the electron spin magnetization vector from z (magnetic field) into xy plane ({pi}/2 pulse); the time evolution of magnetization in xy plane, the free induction decay (FID), is sampled. Fourier transform of FID gives the frequency domain EPR spectrum of the free radicals, and the method is ideal for time-resolved studies of free radicals produced by pulsed-laser ex… more

Date: November 1, 1992

Creator: van Willigen, H.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Surface electronic structure of GaAs(110) studied by Auger photoelectron coincidence spectroscopy

We have used Auger photoelectron coincidence spectroscopy to study the M{sub 4,5}VV Auger spectra of GaAs(110). Using this technique, the Ga and As spectra can be separated and studied independently. The lineshape of the As-M{sub 4,5}VV measured in coincidence with the As 3d photoemission line differs significantly from the conventional Auger spectrum. We attribute this to the surface electronic properties of the system. In addition, we have found that the ss-component of the As spectrum is mor… more

Date: December 31, 1990

Creator: Bartynski, R. A.; Garrison, K.; Jensen, E.; Hulbert, S. L. & Weinert, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Toward a surface photoelectron diffractometer: A progress report on selected advances and an assessment

X-ray diffractometric determination of atomic structures in ordered bulk systems is highly automated and has wide application. By contrast, surface crystallography, whether based on photon or electron scattering, is still in a relatively early stage of development. A summary is given of recent selected highlights in efforts to make progress toward surface photoelectron diffractometry and holography by our Berkeley-Penn State group. It is concluded that an automated photoelectron diffractometer … more

Date: October 6, 1993

Creator: Shirley, D. A; Zheng, Yu; Petersen, B. L.; Hussain, Z.; Huff, W. A.; Barton, J. J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Positron studies in catalysis research. Progress report, September 1993--April 1994, and final report, 15 January 1990--14 January 1994

During the past eight months, the authors have made progress in several areas relevant to the eventual use of positron techniques in catalysis research. They have come closer to the completion of their positron microscope, and at the same time have performed several studies in their non-microscopic positron spectrometer which should ultimately be applicable to catalysis. The current status of the efforts in each of these areas is summarized in the following sections: Construction of the positro… more

Date: June 1, 1994

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Synchrotron Mossbauer Spectroscopy of powder samples

Synchrotron Mossbauer Spectroscopy, SMS, is an emerging technique that allows fast and accurate determination of hyperfine field parameters similar to conventional Mossbauer spectroscopy with radioactive sources. This new technique, however, is qualitatively different from Mossbauer spectroscopy in terms of equipment, methodology, and analysis to warrant a new name. In this paper, the authors report on isomer shift and quadrupole splitting measurements of Mohr`s salt, Fe(NH{sub 4}){sub 2}(SO{su… more

Date: August 1, 1994

Creator: Alp, E. E.; Sturhahn, W. & Toellner, T.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Strain distribution in heterolayers with low misfit as revealed by convergent beam illumination methods

Convergent beam electron diffraction (CBED) was applied to the local measurement of lattice parameter across a strained interface with small mismatch. GaAs layers grown at low temperature with excess As (with 0.15% misfit) on a GaAs substrate were chosen for these studies. Tetragonal distortion was detected in the layer up to 0.5 {mu}m from the interface. With an increase of the layer thickness lowering of the symmetry of these CBED patterns was observed. This lowering of symmetry is most proba… more

Date: November 1, 1992

Creator: Liliental-Weber, Z.; Kaneyama, T.; Terauchi, M. & Tanaka, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Magnetic effects in anomalous dispersion

Spectacular enhancements of magnetic x-ray scattering have been predicted and observed experimentally. These effects are the result of resonant phenomena closely related to anomalous dispersion, and they are strongest at near-edge resonances. The theory of these resonances will be developed with particular attention to the symmetry properties of the scatterer. While the phenomena to be discussed concern magnetic properties the transitions are electric dipole or electric quadrupole in character … more

Date: December 31, 1992

Creator: Blume, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Diffraction tomographic signal processing algorithms for tunnel detection

Signal processing algorithms have been developed for wave based imaging using diffraction tomography. The basis for this image reconstruction procedure is the generalized projection slice theorem (GPST) which, for homogeneous waves, is an analytic relationship between the spatial Fourier transform of the acquired data and the spatial Fourier transform of the spatial profile (object function) of the object being imaged. Imaging within geophysical diffraction tomography when only homogeneous wave… more

Date: August 1, 1993

Creator: Witten, A. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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A Structural Determination Using Magnetic X-Ray Circular Dichroism in Spin-Polarized Photoelectron Diffraction

The first structural determination with spin-polarized, energy-dependent photoelectron diffraction using circularly-polarized x-rays is reported for Fe films on Cu(001). Circularly-polarized x-rays produce spin-polarized photoelectrons from the Fe 2p doublet, and intensity asymmetries in the 2p{sup 3/2} level are observed. . Fully spin-specific multiple scattering calculations reproduce the experimentally determined energy and angular dependences. A new analytical procedure which focuses upon i… more

Date: May 26, 1994

Creator: Waddill, G. D.; Tobin, J. G.; Guo, X. & Tong, S. Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Effects of low-temperature catalytic pretreatments on coal structure and reactivity in liquefaction. Technical progress report, January 1992--March 1992

Low-temperature catalytic pretreatment is a promising approach to the development of an improved liquefaction process. This work is a fundamental study on effects of pretreatments on coal structure and reactivity in liquefaction. The main objectives of this project are to study the coal structural changes induced by low-temperature catalytic and thermal pretreatments by using spectroscopic techniques; and to clarify the pretreatment-induced changes in reactivity or convertibility of coals in th… more

Date: May 1, 1992

Creator: Song, C.; Saini, A. K.; Hatcher, P. G. & Schobert, H. H.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Studies of magnetism at the National Synchrotron Light Source

This report briefly discusses research being conducted on magnetism at the National Synchrotron Light Source.

Date: June 1, 1994

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Neutron and x-ray scattering studies of (FeF{sub 2}){sub m}(CoF{sub 2}){sub n} multilayers

We have performed elastic neutron scattering measurements of the staggered magnetization in (FeF{sub 2}){sub m}(CoF{sub 2}){sub n} superlattices. Thermal expansion measurements, which are proportional to the magnetic contribution to the specific heat, wwre also carried out using high resolution x-ray diffraction. One of the two measured samples has thickness of m = n = 4.5 and the other m = 26 and n = 28 monolayers, as determined from high angle x-ray {theta} - 2{theta} scans. In the m = n = 4.… more

Date: June 1, 1993

Creator: Lederman, D.; Belanger, D. P.; Wang, J.; Han, S. J.; Paduani, C. P.; Ramos, C. A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Suppression of charge scattering in Moessbauer experiments using synchrotron radiation

The extremely small ratio of linewidth to energy combined with the character of recoil free absorption and reemission makes the low lying nuclear resonances a unique spectroscopic tool. Further, considering the simplicity of performing Moessbauer experiments, they have become very useful in a wide range of disciplines. {sup 57}Fe has remained the most widely used isotope despite its low natural abundance (2%) because iron is ubiquitous in nature and shows a strong effect. The energy width of th… more

Date: December 31, 1992

Creator: Bergmann, U.; Siddons, D. P. & Hastings, J. B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Quantification of volume flaw sizes in ceramics by image processing of 3D x-ray tomographic data sets

This paper introduces a technique to quantify internal flaws in a ceramic body. The approach uses data images obtained from 3D X-ray computed tomography. An approach called guided segmentation uses image processing methods applied to a series of the data images to quantify the flaw volumes. The techniques is tested on synthesized data for spheres. The technique is than applied to real images of known size to examine its use.

Date: January 1, 1993

Creator: Stinson, M. C.; Holloway, D. A. & Ellingson, W. A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Magnetic x-ray circular dichroism in Fe Co Pt multilayers

Magnetic x-ray circular dichroism in x-ray absorption has been used to investigate the ternary multilayer system, Fe Co Pt. Samples were prepared by planar magnetron sputter deposition and carefully characterized, using a variety of techniques such as grazing-incidence and high-angle x-ray scattering, Auger depth profiling and cross-section transmission electron microscopy. As previously reported, the Fe9.5{Angstrom} Pt9.5{Angstrom} exhibits a large dichroism in the Fe 2p absorption. Interestin… more

Date: April 1, 1994

Creator: Tobin, J. G.; Jankowski, Alan Frederic; Waddill, G. D. & Sterne, P. A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Positron implantation in solids

The Monte Carlo technique for modeling positron prior to annihilation and electron implantation in semi-infinite metals is described. Particle implantation is modelled as a multistep process, a series of collisions with the atoms of the host material. In elastic collisions with neutral atoms there is no transfer of energy. The particle loses energy by several different channels, excitation of the electron gas, ionization of the ion cores, or, at low energies, by phonon excitation. These competi… more

Date: December 31, 1993

Creator: Ghosh, V. J.; Lynn, K. G. & Welch, D. O.

Item Type: Article

Partner: UNT Libraries Government Documents Department