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  • 1
    Electronic Resource
    Electronic Resource
    Defect dominated charge transport in amorphous Ta2O5 thin films (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 850-862 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ta2O5 is a candidate for use in metal–oxide–metal (MOM) capacitors in several areas of silicon device technology. Understanding and controlling leakage current is critical for successful implementation of this material. We have studied thermal and photoconductive charge transport processes in Ta2O5 MOM capacitors fabricated by anodization, reactive sputtering, and chemical vapor deposition. We find that the results from each of these three methods are similar if one compares films that have the same thickness and electrodes. Two types of leakage current are identified: (a) a transient current that charges the bulk states of the films and (b) a steady state activated process involving electron transport via a defect band. The transient process involves either tunneling conductivity into states near the Fermi energy or ion motion. The steady state process, seen most commonly in films 〈300 Å thick, is dominated by a large number of defects, ∼1019–1020 cm−3, located near the metal–oxide interfaces. The interior of thick Ta2O5 films has a substantially reduced number of defects. Modest heating (300–400 °C) of Ta2O5 in contact with a reactive metal electrode such as Al, Ti, or Ta results in interfacial reactions and the diffusion of defects across the thickness of the film. These experiments show that successful integration of Ta2O5 into semiconductor processing requires a better understanding of the impact of defects on the electrical characteristics and a better control of the metal–Ta2O5 interface. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373747
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  • 2
    Electronic Resource
    Electronic Resource
    Coulomb glass origin of defect-induced dielectric loss in thin-film oxides (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 4016-4018 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dielectric loss in amorphous, thin-film oxide insulators produces a real part of the ac conductivity σ′(ω) that scales as ωs with s∼1. Conventional models explain this frequency dependence by hopping or tunneling of charge between neighboring defect sites. These models fail at low temperatures since they predict that σ′ should vanish at T=0. We observe that the ac conductivity of Ta2O5, ZnO, and SiO2 has a nonzero extrapolated value at T=0. We propose that this behavior is consistent with the predictions of a Coulomb glass, an insulator with a random distribution of charged defects. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1379984
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  • 3
    Electronic Resource
    Electronic Resource
    Quasi-reflexivity, weakly unconditionally convergent series and weak compactness (1969)
    Springer
    Mathematische Annalen 182 (1969), S. 45-54 
    Details
    ISSN: 1432-1807
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01350162
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  • 4
    Electronic Resource
    Electronic Resource
    Prediction of Breaking Strength in Osteoporotic Avian Bone Using Digitized Fluoroscopy, a Low Cost Radiographic Technique (2000)
    Springer
    Calcified tissue international 67 (2000), S. 309-313 
    Details
    ISSN: 1432-0827
    Keywords: Key words: Osteoporosis — Radiography — Bone breaking strength — Avian bone — Fluoroscopy.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract. Bone fragility in caged laying hens is a severe welfare problem, with fracture incidences in commercial flocks of up to 30% of all hens during their life. This fragility has been attributed to osteoporosis, the etiology of which is multifactorial in birds, as in humans, with genetic, environmental, and nutritional components. Greater understanding of the development of the disorder in hens could be obtained from the same kind of in vivo assessments available in human studies of osteoporosis. These high technology techniques for evaluation of bone mineral density (BMD), such as single or dual energy X-ray absorptiometry (SXA or DXA), quantitative computerized tomography (QCT), or attenuation by ultrasound (US), are so far not widely available to nonclinical researchers. We have modified an older X-ray film technique, radiographic absorptiometry (RA) by digitization of the analog video signal from a Philips BV-25 image intensifier, in single pulse fluoroscopy mode, and subsequent computer analysis with the public domain software package, NIH-Image 1.60. Compared with conventional RA, which uses standard X-ray film, our modified technique reduces X-ray exposure and allows the operator to digitize, store, and analyze many more images in a shorter time. We have called this modified technique ``digitized fluoroscopy'' (DF). In a longitudinal study of humeral radiographic density in a flock of 165 laying hens, significant relationships (P 〈 0.001) were observed between assessments made as early as 25 weeks, utilizing this DF technique in the humerus, and breaking strengths (and other postmortem indicators of osteoporosis) measured at 70 weeks. We conclude that DF can predict some eventual parameters of bone mass measured at 70 weeks from 25 to 40 weeks onward in bones from the same site in laying hens. The relationship between DF measurements made in the humerus and postmortem measurements of radiographic density and breaking strength made at another site (tibia) are less strong but still significant from 40 weeks onward.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002230001120
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  • 5
    Electronic Resource
    Electronic Resource
    Thermoluminescence and Ultra-violet Phosphorescence of the Nucleic Acid Bases (1965)
    [s.l.] : Nature Publishing Group
    Nature 208 (1965), S. 1198-1199 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] (1) Thermoluminescence. The samples were prepared as cylindrical pellets of diameter 1-25 cm and depth 1 mm, formed under pressures of about 4 tons/in2. Following irradiation in silicate glass tubes, in the presence of oxygen, glow curves were recorded using a technique identical to that described ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2081198a0
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  • 6
    Electronic Resource
    Electronic Resource
    Thermoluminescence in poly(methyl methacrylate) γ-irradiated at 77°K (1968)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 6 (1968), S. 1283-1296 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Isotactic and atactic poly(methyl methacrylate) containing varying amounts of polymerization initiator and chain-transfer additives, and carefully purified radiation-polymerized material, were γ-irradiated in the dark at liquid nitrogen temperature. On warming to room temperature at a near-linear rate of 20°K./min., a glow peak having a maximum luminescence intensity at 162 ± 8°K. was observed in all samples; an additional peak at 239 ± 7°K. was resolved relatively infrequently. Low luminescence yields precluded an investigation of the spectral distribution of the glow peaks. It is shown that the electron traps associated with the lower temperature peak are most probably the main-chain methyl groups, while the higher temperature glow peak is tentatively associated with escape of electrons from structural defects in a few small crystalline regions of the samples. It is postulated that, for the peak at 162°K., the trapped electrons combine radiatively with luminescence centers when thermally induced rotational motion of the main-chain methyl groups permits sufficient wave-function overlap. Assuming that methods of glow curve analysis proposed for inorganic materials are applicable to organics, first-order recombination kinetics and an activation energy of 0.084 ± 0.006 e. v. are deduced for the intensity maximum at 162°K. This activation energy is in fair agreement with that obtained by Bordoni et al. for an unspecified side-chain motion occurring at similar temperatures, but is only about half the values quoted with some reservations by Powles and by Kawai on the basis of NMR experiments. It was not possible to determine the kinetics of the 239°K. peak with certainty, but an activation energy of 0.432 ± 0.085 e. v. follows from a first-order assumption. The additives present in the samples did not appear to play any significant part as electrontrapping agents; this observation contrasts with some recent work on the visible and ultraviolet absorption spectra of the same materials which showed a close correlation of additional bands developed following irradiation with the presence of specific additives.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1968.160060707
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