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  • 1
    ISSN: 1432-0630
    Keywords: PACS: 61.70; 68.55; 78.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract.  Positron lifetime measurements on bulk samples of single crystal SiC wafers have shown that both 6H and 4H polytypes exhibit a bulk lifetime of 150±2 ps. All samples contained a second, defect-related lifetime component, ranging in value from 250 to about 300 ps with rather low intensities. The defect structure exhibited by the nanocrystalline samples is, not unexpectedly, much more complex. Positron beam experiments on Electron Cyclotron Resonance Chemical Vapour Deposited (ECR-CVD) SiC thin films showed that the positrons are very sensitive to changes in important film parameters as a function of the deposition conditions. It was found that the film density is lower than expected, probably due to hydrogen incorporation; variations in composition among different films were detected through variations in the S parameters, and differences were observed in the electric field at the film–substrate interface due to hydrogen passivation of dangling bonds and different substrate resistivities.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 1799-1804 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modification of GaAs by Si+-ion implantation is an important process for selective doping of the material. Defects caused by the implantation process often lead to incomplete electrical activation, and annealing procedures are used to recover the crystal quality. Results are presented of variable-energy positron (VEP) and cross-sectional transmission electron microscopy (XTEM) studies of a series of GaAs samples implanted with moderate to high fluences of 3×1013, 3×1014, and 1×1015 Si+ ions cm−2. Samples were irradiated at room temperature, and studied both before and after thermal annealing for one hour at 850 °C. In all cases XTEM results show a high density of small extrinsic dislocations after implantation, and VEP shows high concentrations of point (vacancy type) defects. Annealing leads to a decrease in the point-defect concentration in the lowest-fluence sample, but both XTEM and VEP confirm the formation of macroscopic (i.e., (approximately-greater-than)20 A(ring) diameter) voids following annealing. These data are discussed in the context of microscopic models for defect formation and migration.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 52-54 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have applied positron annihilation spectroscopy to examine the formation of voids in SiO2-passivated 1 μm×1 μm Al-0.5 wt. % Cu lines. Samples were heat-treated both ex situ and in the positron beam to monitor void formation as a function of time and temperature. By measuring the fraction of 3-γ annihilations (a sensitive indicator of large open volume defects) we have established that voids are present at the interface between the Al alloy lines and the SiO2 passivation before heat treatment. The 3-γ fraction then grows to a maximum in less than 1 h at a temperature of 300 °C. Changes in the Doppler-broadening S parameter are also observed. Studies are underway to apply the same methodology to investigate electromigration.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2216-2223 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The annealing behavior of amorphous, hydrogenated silicon carbide films in the range 400–900 °C was studied by optical characterization methods, 15N hydrogen profiling, and defect profiling using a variable energy positron beam. The films were deposited in an electron cyclotron resonance chemical vapor deposition system using ditertiary butyl silane [SiH2(C4H9)2] as the monosource for silicon and carbon. As-deposited films were found to contain large concentrations of hydrogen, both bonded and unbonded. Under rapid thermal annealing in a N2 atmosphere, the bonded hydrogen effuses giving rise to additional Si–C bond formation and to film densification. After annealing at high temperatures in N2, a marked decrease in the total hydrogen content is observed. After annealing in vacuum, however, the hydrogen effusion promotes void formation in the films. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Anaesthesia 37 (1982), S. 0 
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The fibrinolytic effects of six different anaesthetic agents were studied in 36 patients undergoing abdominal hysterectomy. Fibrinolytic activity was measured by dilute whole blood and euglobulin clotlysis times. Concentrations of plasminogen, fibrinogen and fibrin degradation products were also determined. Significant enhancement of fibrinolytic activity, measured as a decrease in clotlysis time, was seen during anaesthesia and surgery with all agents studied. Halothane produced the least effect and the greatest increase in fibrinolytic activity was seen during trichloroethylene anaesthesia. Lumbar extradural anaesthesia also consistently produced enhancement of fibrinolysis. The reasons for these results and their clinical implications are discussed.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Anaesthesia 42 (1987), S. 0 
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The influence of anaesthesia on the peri-operative changes in acute phase protein concentrations was studied in 18 patients undergoing elective cholecystectomy. A standard anaesthetic technique was supplemented either by one of two different doses of fentanyl, or by halothane. Eleven proteins were studied but the acute phase response was significantly altered by the anaesthetic technique for only two, fibrinogen and antichymotrypsin. The concentration of these proteins tended to be lower with 2–3 μg/kg fentanyl than with either halothane or fentanyl 12 μg/kg. There was no evidence of variation in stress suppression between the three techniques. The mechanism of any anaesthetic influence on the acute phase response is uncertain and this study is too small to assess its clinical significance.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Anaesthesia 40 (1985), S. 0 
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The performance of the ‘Permox’ oxygen concentrator has been investigated in detail with particular reference to its possible use as an alternative to conventional oxygen supplies both in the emergency situation, in the event of failure of pipeline or cylinder systems or when these are unavailable. The stability and concentrations of oxygen produced at various flows provided a viable alternative supply of oxygen, and the portability and reliability of this particular apparatus made it suitable for use in the many situations considered.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Anaesthesia 40 (1985), S. 0 
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Three possible factors predisposing to Althesin hypersensitivity, namely total dose, method of administration, either by bolus dose or infusion, and pregnancy have been studied in patients receiving the drug for the first time. Of 137 patients given Althesin, four exhibited clinical signs of mild hypersensitivity, while C3 conversion alone, indicative of a subclinical reaction, was seen in a further six patients. No reactions were observed in two control groups in whom anaesthesia was induced with thiopentone. Neither the total dose nor method of administration appeared consistently to influence the incidence of reactions, but eight of the ten patients producing an altered response to Althesin were pregnant.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Anaesthesia 40 (1985), S. 0 
    ISSN: 1365-2044
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Two oxygen concentrators designed for home use, the ‘Healthdyne’ and the ‘Mini O2’, have been assessed with particular reference to their possible role in anaesthesia. Both were found to be a reliable source of oxygen enriched gas. Neither was fully capable of driving a gas powered ventilator satisfactorily, but both could potentially be very useful in normal and field anaesthetic practice.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 2458-2462 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Positron annihilation spectroscopy has been used to study silicon nitride films grown by plasma-enhanced chemical vapor deposition and annealed at different temperatures. For both silicon-rich and nitrogen-rich films, the positron line shape (S) parameter increases after annealing for 15 min at temperatures up to 700–800 °C. This is understood in terms of the fact that removal of the hydrogen by annealing leads to the presence of unpassivated silicon dangling bond sites and vacancy complexes. Annealing at higher temperatures leads to a reduction in the S parameter, consistent with further hydrogen removal producing unpassivated N− sites. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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