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Direct observations of the primary state of radiation damage of ion-irradiated tungsten and platinum

Description: A brief summary was presented of all the Cornell work on the primary state of radiation damage in ion-irradiated tungsten and platinum. The primary research tool for all this research was the field-ion microscope (FIM); the FIM was ideally suited for this research because of its excellent atomic resolution and the ability to examine the interior of the specimens, as a result of the field-evaporation effect. This paper summarized, in outline form, the following items: (1) the principal experimen… more
Date: July 1, 1980
Creator: Seidman, D. N.; Current, M. I.; Pramanik, D. & Wei, C. Y.
Partner: UNT Libraries Government Documents Department
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Ion-induced surface modification of alloys

Description: In addition to the accumulation of the implanted species, a considerable number of processes can affect the composition of an alloy in the surface region during ion bombardment. Collisions of energetic ions with atoms of the alloy induce local rearrangement of atoms by displacements, replacement sequences and by spontaneous migration and recombination of defects within cascades. Point defects form clusters, voids, dislocation loops and networks. Preferential sputtering of elements changes the c… more
Date: November 1, 1983
Creator: Wiedersich, H.
Partner: UNT Libraries Government Documents Department
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Electron beam induced oxygen in YBa sub 2 Cu sub 3 O sub 7-x superconductors

Description: Thin foils of bulk YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) superconductors were subjected to electron irradiation in a Transmission Electron Microscope (TEM). The resulting disordering of the oxygen atoms and vacancies in the Cu-O planes was monitored by measuring the splitting of the (110) diffraction spots in the (001) diffraction pattern. Samples were irradiated at 83K with 100, 150, 200 and 300kV electrons. The 100kV electrons did not cause any disordering, even after prolonged irradiation. Th… more
Date: January 1, 1989
Creator: Basu, S.N.; Roy, T.; Mitchell, T.E. & Nastasi, M.
Partner: UNT Libraries Government Documents Department
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Variable-energy positron studies of well-annealed single-crystal Cd samples from 35 to 450 K

Description: Well-annealed Cd(001) and Cd(100) samples have been examined using a monoenergetic variable-energy positron beam (0.5 to 5.0 keV). The results are interpreted in the context of a one-dimensional-diffusion model which allows for annihilations as well as trapping at defects including thermally generated vacancies. The dependence on temperature of positron diffusion out of these samples was determined by the use of this model to interpret data taken between 35 and 450 K. The deduced positron diffu… more
Date: January 1, 1982
Creator: Lynn, K.G.; Goland, A.N.; Schultz, P.J.; Vehanen, A. & MacKenzie, I.K.
Partner: UNT Libraries Government Documents Department
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Electron microscopy of ceramic superconductors

Description: The critical current Jc is at least as important as Tc (transition temperature) for applications in superconducting materials. Jc is strongly dependent on microstructure and, in consequence, electron microscopy will continue to be important in the development of practical ceramic superconductors. We will review the progress that has been made over the past year or so in studying the superconductors by electron microscopy techniques of all kinds--conventional, high resolution, analytical, etc. A… more
Date: January 1, 1988
Creator: Mitchell, T.E. & Roy, T.
Partner: UNT Libraries Government Documents Department
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The feasibility of welding of irradiated materials

Description: Helium was implanted into solution-annealed (SA) 316 stainless steel, 20% cold-worked (CW) 316 stainless steel and titanium-modified Primary Candidate Alloy (PCA) through tritium decay to levels ranging from 0.18 to 256 appm. Full penetration welds were then made on helium-doped materials using gas tungsten arc welding (GTAW) under fully constrained conditions. Intergranular heat-affected zone (HAZ) cracking was observed in all of the materials containing greater than 1 appm He. Electron micros… more
Date: January 1, 1989
Creator: Lin, H. T.; Chin, B. A. (Oak Ridge National Lab., TN (USA) & Auburn Univ., AL (USA). Dept. of Materials Engineering)
Partner: UNT Libraries Government Documents Department
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Vacancies in thermal equilibrium in Nb

Description: We have measured the diffusion of positrons in Nb(110) in the temperature range from 300K to 2450K utilizing a variable energy positron beam. The purpose was to study the vacancy formation. However, no significant sign of vacancy trapping was observed. This could be due to a high detrapping rate caused by a low positron binding energy or due to a high vacancy formation enthalpy H/sub IV//sup F/. The last possibility is consistent with recent studies of the vacancy migration and with calculation… more
Date: June 1, 1985
Creator: Nielsen, B.; Lynn, K.G.; Hurst, J.; Vehanen, A. & Schultz, P.J.
Partner: UNT Libraries Government Documents Department
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Positron-annihilation studies of molybdenum irradiated by protons, neutrons, or electrons

Description: Annealed molybdenum was irradiated at room temperature by energetic protons or neutrons and the fluence and recoil energy dependence of two traps was measured. Comparison of trapping rates with calculations of damage energy correlates high energy recoils with the short lifetime trap and low energy recoils with the longer lifetime.
Date: March 26, 1982
Creator: Howell, R.H.
Partner: UNT Libraries Government Documents Department
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Evidence for shallow positron traps in a neutron-irradiated Al single crystal

Description: Variable energy positrons have been used to determine the dependence on temperature of positron diffusion out of a neutron-irradiated single crystal of Al. The results are interpreted in the context of a one-dimensional diffusion model which includes bulk annihilations as well as trapping at voids and other microstructural defects in the bulk material by way of a removal rate kappa/sub eff/ of freely diffusing positrons. The data show a strongly negative dependence on temperature below 125/sup … more
Date: January 1, 1982
Creator: Schultz, P. J.; MacKenzie, I. K.; Lynn, K. G.; West, R. N. & Snead, C. L. Jr.
Partner: UNT Libraries Government Documents Department
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Radiation damage studies on natural rock salt from various geological localities of interest to the radioactive waste disposal program

Description: As part of a program to investigate radiation damage in geological materials of interest to the radioactive waste disposal program, radiation damage, particularly radiation induced sodium metal colloid formation, has been studied in 14 natural rock salt samples. All measurements were made with equipment for making optical absorption and other measurements on samples, in a temperature controlled irradiation chamber, during and after 0.5 to 3.0 MeV electron irradiation. Samples were chosen for pr… more
Date: January 1, 1981
Creator: Levy, P.W.
Partner: UNT Libraries Government Documents Department
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Sputtering of tungsten: an atomic view of a near-surface depleted zone created by a single 30 keV /sup 63/Cu/sup +/ projectile. Report No. 4118

Description: The vacancy structure of a near-surface depleted zone (DZ), created by a single 30 keV /sup 63/Cu/sup +/ ion in a tungsten field-ion microscope (FIM) specimen, was determined with atomic resolution. Both the irradiation and pulse field-evaporation experiments were performed in situ at less than or equal to 11 K, so that the observed vacancy structure was unaltered by the long-range migration of self-interstitial atoms. The following basic physical quantities were measured: (1) the number of vac… more
Date: January 1, 1979
Creator: Current, M. I. & Seidman, D. N.
Partner: UNT Libraries Government Documents Department
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Positron-annihilation 2D-ACAR studies of disordered and defected alloys

Description: Theoretical and experimental progess in connection with 2D-ACAR positron annihilation studies of ordered, disordered, and defected alloys is discussed. We present, in particular, some of the recent developments concerning the electronic structure of disordered alloys, and the work in the area of annihilation from positrons trapped at vacancy-type defects in metals and alloys. The electronic structure and properties of a number of compounds are also discussed briefly; we comment specifically on … more
Date: September 1, 1987
Creator: Bansil, A.; Prasad, R.; Smedskjaer, L. C.; Benedek, R. & Mijnarends, P. E.
Partner: UNT Libraries Government Documents Department
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Recovery of neutron-irradiated high-purity Si

Description: High-purity Si single crystals have been neutron irradiated at approx.100/sup 0/C to several fluences to 2 x 10/sup 20/ n/cm/sup 2/ (E > 1 MeV). Isochronal-annealing results using lifetime and Doppler broadening indicate a complex microstructural evolution of the Si with annealing temperature for the highest dose, going from divacancy, to quadrivacancy, to dislocation dominance of the trapping over four orders of magnitude in fluence. The lowest fluence features only divacancy effects.
Date: January 1, 1985
Creator: Snead, C. L. Jr. & Lynn, K. G.
Partner: UNT Libraries Government Documents Department
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Theoretical investigations of two Si-based spintronic materials

Description: Two Si-based spintronic materials, a Mn-Si digital ferromagnetic heterostructure ({delta}-layer of Mn doped in Si) with defects and dilutely doped Mn{sub x}Si{sub 1-x} alloy are investigated using a density-functional based approach. We model the heterostructure and alloy with a supercell of 64 atoms and examine several configurations of the Mn atoms. We find that 25% substitutional defects without vacancies in the {delta} layer diminishes half metallicity of the DFH substantially. For the allo… more
Date: August 3, 2007
Creator: Fong, C Y; Snow, R; Shaughnessy, M; Pask, J E & Yang, L H
Partner: UNT Libraries Government Documents Department
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Ferromagnetism in GaN: Gd: A density functional theory study

Description: First principle calculations of the electronic structure and magnetic interaction of GaN:Gd have been performed within the Generalized Gradient Approximation (GGA) of the density functional theory (DFT) with the on-site Coulomb energy U taken into account (also referred to as GGA+U). The ferromagnetic p-d coupling is found to be over two orders of magnitude larger than the s-d exchange coupling. The experimental colossal magnetic moments and room temperature ferromagnetism in GaN:Gd reported re… more
Date: February 4, 2008
Creator: Stevenson, Cynthia & Stevenson, Cynthia
Partner: UNT Libraries Government Documents Department
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Hydrogen adsorption on Ru(001) studied by Scanning TunnelingMicroscopy

Description: The adsorption of hydrogen on Ru(001) was studied by scanning tunneling microscopy at temperatures around 50 K. Hydrogen was found to adsorb dissociatively forming different ordered structures as a function of coverage. In order of increasing coverage {theta} in monolayers (ML) these were ({radical}3 x {radical}3)r30{sup o} at {theta} = 0.3 ML; (2 x 1) at {theta} = 0.50 ML, (2 x 2)-3H at {theta} = 0.75, and (1 x 1) at {theta} = 1.00. Some of these structures were observed to coexist at intermed… more
Date: January 18, 2008
Creator: Tatarkhanov, Mous; Rose, Franck; Fomin, Evgeny; Ogletree, D.Frank & Salmeron, Miquel
Partner: UNT Libraries Government Documents Department
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Ferromagnetism in tetragonally distorted LaCoO3 thin films

Description: Thin films of epitaxial LaCoO{sub 3} were synthesized on SrTiO{sub 3} and (La, Sr)(Al, Ta)O{sub 3} substrates varying the oxygen background pressure in order to evaluate the impact of epitaxial growth as well as oxygen vacancies on the long range magnetic order. The epitaxial constraints from the substrate impose a tetragonal distortion compared to the bulk form. X-ray absorption and x-ray magnetic circular dichroism measurements confirmed that the ferromagnetism arises from the Co ions and per… more
Date: September 17, 2008
Creator: Mehta, Virat Vasav; Liberati, Marco; Wong, Franklin J.; Chopdekar, Rajesh Vilas; Arenholz, Elke & Suzuki, Yuri
Partner: UNT Libraries Government Documents Department
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Remarkable Strontium B-Site Occupancy in FerroelectricPb(Zr1-xTix)O3 Solid Solutions Doped with Cryolite-Type StrontiumNiobate

Description: New high-performance ferroelectric materials based on Pb(Zr{sub 1-x}Ti{sub x})O{sub 3} (PZT) that are doped with cryolite-type strontium niobate (SNO, Sr{sub 4}(Sr{sub 2-2y/3}Nb{sub 2+2y/3})O{sub 11+y}V{sub 0,1-y} with 0 {le} y {le} 1), hence denoted PZT:SNO, and their microscopic structure are described. The combination of exceptional piezoelectric properties, i.e. a piezoelectric strain constant of d{sub 33} {approx} 760 pm/V, with excellent stability and degradation resistance makes ferroele… more
Date: April 26, 2007
Creator: Feltz, A.; Schmidt-Winkel, P.; Schossman, M.; Booth, C.H. & Albering, J.
Partner: UNT Libraries Government Documents Department
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PASSIVITY BREAKDOWN AND EVOLUTION OF LOCALIZED CORROSION ON TYPE 316L STAINLESS STEEL

Description: Passivity breakdown of 316L SS in the presence of aggressive Cl{sup -} and inhibitive NO{sub 3}{sup -} anions has been experimentally studied and the results have been interpreted in terms of the Point Defect Model (PDM). By introducing the competitive adsorption of Cl{sup -} and NO{sub 3}{sup -} into surface oxygen vacancies at the passive film/solution interface, the PDM yields a critical breakdown potential (V{sub c}) that is predicted to vary linearly with log[Cl{sup -}], or with log ([Cl{s… more
Date: October 23, 2006
Creator: S. Yang, G. Engelhardt, and D. D. Macdonald
Partner: UNT Libraries Government Documents Department
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Characteristics of CoxTi1-xO2 thin films deposited by MOCVD

Description: This paper deals with the growth and characterization of ferromagnetic cobalt doped TiO{sub 2} thin films deposited by liquid precursor metal organic chemical vapor deposition (MOCVD) using a new combination of the source materials Co(TMHD){sub 3}, tetrahydrofuran (THF), and titanium isopropoxide (TIP). An array of experiments reveals the intrinsic ferromagnetic nature of the grown films, and suggests that the magnetism is not generated by oxygen vacancies.
Date: May 9, 2008
Creator: McClure, A.; Kayani, A.; Idzerda, Y.U.; Arenholz, E. & Cruz, E.
Partner: UNT Libraries Government Documents Department
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Good electrical contacts for high resistivity (Cd,Mn)Te crystals

Description: We consider that semi-insulating (Cd,Mn)Te crystals may well successfully replace the commonly used (Cd,Zn)Te crystals as a material for manufacturing large-area X- and gamma-ray detectors. The Bridgman growth method yields good quality and high-resistivity (10{sup 9}-10{sup 10} {Omega}-cm) crystals of (Cd,Mn)Te:V. Doping with vanadium ({approx} 10{sup 16} cm{sup -3}), which acts as a compensating agent, and annealing in cadmium vapors, which reduces the number of cadmium vacancies in the as-gr… more
Date: October 19, 2008
Creator: Witkowska-Baran, M.; Mycielski, A.; Kochanowska, D.; Szadkowski, A. J.; Jakiela, r.; Witkowska, B. et al.
Partner: UNT Libraries Government Documents Department
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Atomic Structure of Pyramidal Defects in GaN:Mg; Influence ofAnnealing

Description: The atomic structure of the characteristic defects (Mg-rich hexagonal pyramids) in p-doped bulk and MOCVD GaN:Mg thin films grown with Ga polarity was determined at atomic resolution by direct reconstruction of the scattered electron wave in a transmission electron microscope. Small cavities were present inside the defects, confirmed also with positron annihilation. The inside walls of the cavities were covered by GaN of reverse polarity compared to the matrix. Defects in bulk GaN:Mg were almos… more
Date: October 3, 2005
Creator: Liliental-Weber, Z.; Tomaszewicz, T.; Zakharov, D.; O'Keefe, M.; Hautakangas, S.; Saarinen, K. et al.
Partner: UNT Libraries Government Documents Department
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The charge state of iron implanted into sapphire

Description: Several techniques (RBS, TEM, CEMS) have been used to characterize sapphire single crystals implanted with iron at room temperature to fluences of 10/sup 16/ to 10/sup 17/ ions cm/sup -2/. At low fluences the as-implanted iron is found mainly in the ferrous state. As the fluence is increased, Fe/sup 3 +/ and metallic iron clusters became dominant. There is a strong correlation between the probability of finding specific configurations of iron ions within four cation coordination shells and the … more
Date: August 1, 1987
Creator: McHargue, C. J.; Sklad, P. S.; White, C. W.; Farlow, G. C.; Perez, A.; Kornilios, N. et al.
Partner: UNT Libraries Government Documents Department
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