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  • 1
    Digitale Medien
    Digitale Medien
    Dynamics of a gravitational billiard with a hyperbolic lower boundary (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 9 (1999), S. 841-848 
    Details
    ISSN: 1089-7682
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Gravitational billiards provide a simple method for the illustration of the dynamics of Hamiltonian systems. Here we examine a new billiard system with two parameters, which exhibits, in two limiting cases, the behaviors of two previously studied one-parameter systems, namely the wedge and parabolic billiard. The billiard consists of a point mass moving in two dimensions under the influence of a constant gravitational field with a hyperbolic lower boundary. An iterative mapping between successive collisions with the lower boundary is derived analytically. The behavior of the system during transformation from the wedge to the parabola is investigated for a few specific cases. It is surprising that the nature of the transformation depends strongly on the parameter values. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.166467
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  • 2
    Digitale Medien
    Digitale Medien
    Relationship between electroluminescence and current transport in organic heterojunction light-emitting devices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7991-8006 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We measure the current–voltage and electroluminescence characteristics of single-heterojunction, vacuum-deposited organic light-emitting devices (OLEDs) over a wide range of materials, temperatures, and currents. We find that the current is limited by a large density of traps with an exponential energy distribution below the lowest unoccupied molecular orbital. The characteristic trap depth is 0.15 eV. Furthermore, in metal–quinolate-based devices, electroluminescence originates from recombination of Frenkel excitons, and its temperature dependence is consistent with the excitons being formed by Coulombic relaxation of the trapped electrons with holes injected from the counter electrode. By semiempirical molecular orbital modeling, we find that the trap distribution obtained from the current–voltage characteristics is consistent with a distribution in the metal–quinolate molecular conformations which result in a continuous, exponential distribution of allowed states below the lowest unoccupied molecular orbital. We discuss the implications of the intrinsic relationship between electroluminescence and current transport in OLEDs for the optimization of efficiency and operating voltage in these devices. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.362350
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  • 3
    Digitale Medien
    Digitale Medien
    Organic films deposited on Si p-n junctions: Accurate measurements of fluorescence internal efficiency, and application to luminescent antireflection coatings (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4644-4648 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Ultraviolet (UV) optical pumping followed by fluorescence wavelength downconversion of thin film organic light emitting materials deposited directly on the surface of Si p-n junction diodes is found to be an accurate and rapid means to determine the film internal fluorescence efficiency. By measuring the photoresponse of the Si detectors in the UV, we find that the organic light emitting films of aluminum tris-(8-hydroxyquinoline) (Alq3), N,N′-diphenyl-N,N′-bis-(3-methylphenyl)- 1,1′-biphenyl-4,4′-diamine, and bis-(8-hydroxyquinaldine)-chlorogallium (Gaq2′Cl), have internal fluorescence efficiencies of 0.30±0.05, 0.35±0.03, and 0.36±0.03, respectively. It has also been found that the organic films can be grown to a thickness which optimizes UV light conversion and can, at the same time, serve as antireflection coatings in the visible spectral region, thereby resulting in enhanced Si photodiode sensitivity extending from the UV to the infrared. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363447
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  • 4
    Digitale Medien
    Digitale Medien
    Pulsed laser induced epitaxial crystallization of carbon–silicon alloys (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4118-4123 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Nonequilibrium Si1−xCx alloys produced by pulsed laser induced epitaxy from ion implanted Si have been studied in the concentration range from 0.35 to 3.8 at. % C. Films were formed by multiple energy ion implantation of carbon into {001} Si to produce nearly uniform composition profiles, followed by irradiation with a 308 nm, 30 ns excimer laser pulse. Heteroepitaxy proceeded from the underlying {001} Si through the carbon containing layer at approximately 5 m/s. Transmission electron microscopy, Fourier transform infrared spectroscopy, high resolution x-ray diffraction, ion channeling, and secondary-ion mass spectrometry were used to characterize the structure and composition. At low concentrations, the films are fully strained and the carbon is substitutional. At concentrations exceeding 1.4 at. % C, SiC precipitates were observed and the substitutional carbon concentration decreased. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.361775
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  • 5
    Digitale Medien
    Digitale Medien
    Integrated three-color organic light-emitting devices (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3117-3119 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report a demonstration of the integration of individual polymer-based light emitting devices of three different colors on the same substrate. Orange, green, and blue color devices are sequentially fabricated on the same indium–tin oxide (ITO) coated glass substrate coated with a patterned insulator on the ITO, by the spin coating of polymer thin films, the vacuum deposition of top metal contacts, and the patterning of polymer thin film by plasma etching, using the top metal contacts as the self-aligned etching mask. The devices exhibit no degradation of device characteristics due to the integration processing compared to discrete devices on separate substrates. This demonstration shows a new path towards the fabrication of high performance low-cost full-color organic flat panel displays. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.116800
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  • 6
    Digitale Medien
    Digitale Medien
    Color-tunable organic light-emitting devices (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2959-2961 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We demonstrate an integrated, two-color organic light-emitting device for flat-panel display applications. The device utilizes a unique stacked pixel architecture which allows for independent tuning of color and intensity. Each of the two addressable colors is sufficiently bright for video display applications, so that the compact stacked pixel, which maximizes display resolution, may form the basis of a new type of full-color display. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.117743
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  • 7
    Digitale Medien
    Digitale Medien
    Poly(p-phenylene vinylene)/tris(8-hydroxy) quinoline aluminum heterostructure light emitting diode (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 653-655 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Results are presented from polymer/molecular organic heterostructure light emitting diodes composed of a layer of the conjugated conducting polymer poly(p-phenylene vinylene) (PPV), and a layer of fluorescent molecular compound tris(8-hydroxy) quinoline aluminum (Alq). The external quantum efficiency of these heterostructure LEDs is ∼0.1%, which is over one order of magnitude higher than that of simple PPV LEDs. The electroluminescence (EL) spectra indicate that both materials in the device emit comparable amounts of light. The dependence of the EL spectra on the layer thicknesses and its independence on bias suggest that neutral excitons are formed in the Alq, far from the PPV/Alq interface, and subsequently diffuse into the PPV layer. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.114119
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  • 8
    Digitale Medien
    Digitale Medien
    Behavior of intrinsic Si point defects during annealing in vacuum (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1558-1560 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using B and Sb doped Si(100) doping superlattices (DSL) as tracers of native Si point defect behavior it is shown that vacuum annealing at 810 °C leads to a depletion of Si self-interstitials, with their smallest concentration at the surface, but does not affect the vacancy population. At a fixed depth, the interstitial concentration drops for increasing annealing times; for a given time, the interstitial concentration increases into the sample as a function of depth. Inert anneals of a B-DSL in Ar show flat interstitial profiles. Apparently, the vacuum anneal makes the surface a better sink for interstitials than an inert Ar anneal, leading to an equilibrium interstitial concentration below the value in the bulk and establishing a net outflow of interstitials to the surface. The absence of a response of the vacancy population yields a lower limit on the interstitial-vacancy recombination time of 104 s at 810 °C. Process simulation of this scenario captures the essential trends of the experimental data. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.114733
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  • 9
    Digitale Medien
    Digitale Medien
    Transparent organic light emitting devices (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 2606-2608 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the demonstration of transparent organic light emitting devices (OLEDs) which are ∼70% transparent throughout the visible spectrum when switched off, and emit light from both sides with a total external quantum efficiency of ∼0.1% when turned on. The devices are Alq3-based single heterostructure OLEDs grown on an ITO-coated glass substrate with a top electrode composed of a very thin layer of Mg–Ag and an overlaying ITO film. The top electrode is both electron injecting and transparent. The transparent OLEDs are expected to be useful in high-resolution full-color displays, as well as for helmet-mounted, windshield-mounted, or other "head-up'' display applications. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.116196
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  • 10
    Digitale Medien
    Digitale Medien
    Effect of routine screening for Down's syndrome on the significance of isolated fetal hydronephrosis (1998)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 105 (1998), S. 0 
    Details
    ISSN: 1471-0528
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Objective To determine the risk of Down's syndrome in fetuses with isolated hydronephrosis at 18–23 weeks in an unselected general population after routine screening for Down's syndrome, using first trimester nuchal translucency measurement and second trimester maternal serum biochemistry.Population All pregnant women undergoing a routine 18–23 week ultrasound scan, from a population who had been offered screening for Down's syndrome.Setting A district general hospital serving a low risk obstetric population.Methods Prospective study of all routine 18–23 weeks ultrasound scans. The prevalence of isolated hydronephrosis and Down's syndrome was determined and the relative risk for Down's syndrome was calculated for different ultrasound findings.Results 10,971 women were scanned at 18–23 weeks during the study period. Down's syndrome was diagnosed in 14 of 20 cases before this stage using first trimester nuchal translucency measurement and second trimester maternal serum biochemistry. Isolated fetal hydronephrosis was diagnosed in 423 pregnancies (3.9%); none of these pregnancies were affected by Down's syndrome. The relative risk for Down's syndrome was 0.18 (95% CI 0.06–0.53) for women with a normal scan (n= 9983). When multiple ultrasound markers were found (n= 565), the relative risk for Down's syndrome was 2.00 (95% CI 0.18–22-10) and 9.00 (95% CI 1.14–71.30) for all other aneuploidies.Conclusion The finding of isolated fetal hydronephrosis does not significantly increase the age-related risk for Down's syndrome. The presence of multiple ultrasound markers is associated with an increased risk of aneuploidies other than Down's syndlome. These findings are explained by the reduced prevalence of Down's syndrome as a result of prior screening and diagnosis of this condition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1471-0528.1998.tb10230.x
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