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  • American Institute of Physics (AIP)  (310)
  • 2000-2004  (310)
  • 1
    Electronic Resource
    Electronic Resource
    Influence of a partially oxidized calcium cathode on the performance of polymeric light emitting diodes (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1376-1382 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the influence of the presence of oxygen during the deposition of the calcium cathode on the structure and on the performance of polymeric light emitting diodes (pLEDs). The oxygen background pressure during deposition of the calcium cathode of polymeric LEDs was varied. Subsequently, the oxygen depth distribution was measured and correlated with the performance of the pLEDs. The devices have been fabricated in a recently built ultraclean setup. The polymer layers of the pLEDs have been spincoated in a dry nitrogen atmosphere and transported directly into an ultrahigh vacuum chamber where the metal electrodes have been deposited by evaporation. We used indium–tin–oxide as anode, OC1C10 PPV as electroluminescent polymer, calcium as cathode, and aluminum as protecting layer. We achieved reproducibility of about 15% in current and brightness for devices fabricated in an oxygen atmosphere of (very-much-less-than)10−9 mbar. For further investigations the calcium deposition was carried out in an oxygen atmosphere from 10−8 to 10−5 mbar. We determined the amount of oxygen in the different layers of the current–voltage-light characterized pLEDs with elastic recoil detection analysis and correlated it with the characteristics of the devices. The external efficiency of the pLEDs decreases continuously with increasing oxygen pressure, the current shows a pronounced minimum. The brightness mostly decreases with increasing oxygen with an indication of a slight minimum. PLEDs with completely oxidized calcium are not operational. The first contact of the pLEDs with the dry glove box environment leads to an immediate reduction of current and brightness which is caused by the cooling of the devices by several degrees. Determining reproducible characteristics of pLEDs in the vacuum requires the measurement of their temperature. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1383577
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  • 2
    Electronic Resource
    Electronic Resource
    Progress in internal transport barrier plasmas with lower hybrid current drive and heating in JET (Joint European Torus) : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2156-2164 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In optimized shear plasmas in the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)], safety factor (q) profiles with negative magnetic shear are produced by applying lower hybrid (LH) waves during the plasma current ramp-up phase. These plasmas produce a barrier to the electron energy transport. The radius at which the barrier is located increases with the LH wave power. When heated with high power from ion cyclotron resonance heating and neutral beam injection, they can additionally produce transient internal transport barriers (ITBs) seen on the ion temperature, electron density, and toroidal rotation velocity profiles. Due to recent improvements in coupling, q profile control with LH current drive in ITB plasmas with strong combined heating can be explored. These new experiments have led to ITBs sustained for several seconds by the LH wave. Simulations show that the current driven by the LH waves peaks at the ITB location, indicating that it can act in the region of low magnetic shear. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1469026
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  • 3
    Electronic Resource
    Electronic Resource
    Quantitative diode laser absorption spectroscopy near 2 μm with high precision measurements of CO2 concentration (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 4228-4233 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A diode laser sensor was developed to measure CO2 concentration using absorption spectroscopy at 2 μm. The simplicity of the optical setup and detection electronics makes this spectrometer very compact and well suited for field studies, while the use of optical fibers enables one to probe remote environments. This sensor is capable of providing absolute measurements, with the concentration being inferred from the directly measured absorption spectra, without using calibration cells. This ensures versatility as well as widespread applicability, and a linear response over a large dynamic range. Its analytical capabilities were carefully tested by a large variety of measurements, also with use of a certified CO2/air mixture. The precision of mixing ratio retrievals was about 0.2% while the accuracy was 0.9% for measurements of ambient CO2 concentration. The spectrometer is also capable of providing high precision measurements of the water vapor concentration in ambient air. Specifically, simultaneous detection of both molecular species is demonstrated. Although the performance of our spectrometer can be improved with some effort, it is already competitive with commercially available infrared gas analyzers for atmospheric monitoring applications. In addition, it is an attractive tool for continuous measurements of volcanic gas concentrations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1406929
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  • 4
    Electronic Resource
    Electronic Resource
    Spin-glass-like static and dynamic properties of mechanically alloyed Fe–Re–Cr (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6534-6536 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of spin-glass-like features in a Fe61Re30Cr9 sample obtained after high energy milling for 460 h. X-ray diffraction showed a broad nanocrystalline peak. The zero-field-cooled and field-cooled magnetization curves exhibited a clear irreversibility, the former showing a relatively sharp maximum for low fields at Tmax(approximate)60 K. In addition, the temperature dependence of the magnetic AC susceptibility (χac) also showed a peak at approximately the same temperature. The frequency sensitivity of such maximum (p=ΔTmax/TmaxΔ log w(approximate)0.02) is small compared to that of typical superparamagnets. However, we discuss the insufficiency of this set of phenomena to assert the existence of a true spin-glass transition and propose the blocking of interacting ferromagnetic nanoparticles as the origin of the observed behavior. The effect of annealing, rendered into nanocrystallite growth, on the χac maximum is studied in an attempt to test this explanation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372761
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  • 5
    Electronic Resource
    Electronic Resource
    Thermally enhanced frequency upconversion in Nd3+-doped fluoroindate glass (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4498-4501 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multiphonon assisted frequency upconversion was observed in a Nd3+-doped fluoroindate glass pumped at 866 nm. A near-infrared upconverted emission at 750 nm with a peculiar linear dependence with the laser intensity was observed and explained. The intensity of the upconverted emission experienced a 40-fold enhancement when the sample's temperature was varied from 298 to 498 K. A rate equation model that includes light pumping and multiphonon absorption via thermally coupled electronic excited states of Nd3+ was used, describing quite well the experimental results. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1410326
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  • 6
    Electronic Resource
    Electronic Resource
    Direct observation of local hot electron transport through Al2O3 tunnel junctions (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 1076-1078 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A modified ballistic electron emission microscopy (BEEM) technique using local transport of hot electrons through a buried interface, was successfully applied to study the Al2O3 barrier in the Co/Al2O3/Ru tunnel junction. This technique enabled us to straightforwardly measure an effective barrier height of 1.7 eV and to observe the rise of the barrier height due to continuous current injection into a single point of the junction attributed to charging effects and/or degradation of the barrier structure. Scanning over an area of 510 nm×510 nm showed a spatial inhomogenity of the barrier resulting in different dependencies of the BEEM current on the energy of the injected electrons. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448160
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  • 7
    Electronic Resource
    Electronic Resource
    Dependence of the emission wavelength on the internal electric field in quantum-dot laser structures grown by metal–organic chemical-vapor deposition (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 1435-1437 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show that the combination of different electric fields in In0.5Ga0.5As/GaAs quantum-dot electroluminescent devices dramatically blueshifts the emission wavelength even though the photoluminescence occurs at the expected value of 1.3 μm at room temperature. Systematic photoluminescence (PL), electroluminescence (EL), and photocurrent measurements demonstrate that the electric field associated with the built-in dipole in the dots, directed from the base of the dots to their apex, and the device junction field lead to the depletion of the ground state. As a consequence, structures grown on n-type GaAs substrates exhibit electroluminescence only from the excited states (whereas the photoluminescence comes from the ground level). Instead, by growing the same device structure on p-type GaAs substrates, i.e., by reversing the direction of the built-in electric field of the device, the effect of the permanent dipole is strongly reduced, thus allowing us to obtain EL emission at the designed wavelength of 1.3 μm at 300 K, coincident to the PL. This effect expands the possibilities for the achievement of efficient lasing in the spectral region of interest for optical transmission. The electric field associated to the dipole moment is estimated to be around 150 kV/cm. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1400088
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  • 8
    Electronic Resource
    Electronic Resource
    Large magnetoresistance using hybrid spin filter devices (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 625-627 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A magnetic "spin filter" tunnel barrier, sandwiched between a nonmagnetic metal and a magnetic metal, is used to create a magnetoresistive tunnel device, somewhat analogous to an optical polarizer-analyzer configuration. The resistance of these trilayer structures depends on the relative magnetization orientation of the spin filter and the ferromagnetic electrode. The spin filtering in this configuration yields a previously unobserved magnetoresistance effect, exceeding 100%. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1436284
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  • 9
    Electronic Resource
    Electronic Resource
    Stability of the interface between indium-tin-oxide and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) in polymer light-emitting diodes (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2255-2257 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A cause for degradation of polymer light-emitting diodes is the oxidation of the polymer by oxygen diffusing out of the indium-tin-oxide (ITO) anode. This problem can be solved by the introduction of an organic hole-injecting film, poly-(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS), between the ITO and the emissive polymer. Indeed, a dramatic improvement of the lifetime and also the luminous efficiency has been observed. However, our Rutherford backscattering (RBS) studies show that the ITO/PEDOT:PSS interface is not stable. In as prepared glass/ITO/PEDOT:PSS samples 0.02 at. % indium was found in the PEDOT:PSS film. Annealing in a nitrogen atmosphere at 100 °C during 2500 h increased the indium concentration to 0.2 at. %. Upon exposure to air much faster degradation of the ITO/PEDOT:PSS interface was observed; after several days in air the amount of indium reached a saturation concentration of 1.2 at. %. The degradation of the interface can be explained by etching of the ITO due to the strong acidic nature of PEDOT:PSS. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1315344
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  • 10
    Electronic Resource
    Electronic Resource
    k-cosymplectic manifolds and Lagrangian field theories (2001)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 42 (2001), S. 2092-2104 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A geometrical description of classical field theories of first order is given. The underlying k-cosymplectic structure permits to derive the corresponding field equations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1360997
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