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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 5554-5560 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We investigate the transient electroluminescence (EL) from organic light-emitting diodes based on tristilbeneamine dispersed in polysulfone. An EL overshoot is observed a few microsecond after reversing the driving voltage. The amplitude of the EL spike can considerably exceed the previous EL level. The maximal EL intensity is strongly influenced by temperature, time duration of voltage pulse, and magnitude of reverse voltage. The time integrated overshoot intensity of EL scales as a power law with the pulse length. We attribute the overshoot effect to (i) the accumulation of holes on the interface formed by a polymer and a thin insulating layer of aluminum oxide next to the aluminum cathode under application of positive bias and (ii) the drift of holes back to the anode when the external field is being reversed and recombination with electrons in the bulk of the material. It turns out that the surface roughness of the Al2O3 layer is important for the recombination kinetics under reverse bias. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1823-1826 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A simple analytic model for the electroluminescence (EL) intensity and the total cell current in bilayer light-emitting diodes (LEDs) with Ohmic contacts is presented. Results are in good agreement with both existing experimental data and numerical simulations. This model permits the semiquantitative analyses of the influence of the most important parameters on the EL and cell currents. In particular, dependence of EL current on the ratio of electron to hole mobilities and on the LED geometry is analyzed. The predictions of the model are compared with analogous results for LEDs with barrier-limited injection of electrons. It is shown that the values of EL currents can be comparable. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 2690-2698 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have investigated a multilayer organic light-emitting diode with 1,3,5-tris (N,N-bis-(4-methoxyphenyl)aminophenyl)-benzene acting as the hole transporting layer (HTL) and tris (8-hydroxy-quinolinolato) aluminum (Alq3) as the electron transporting layer. Positive charge carriers in the HTL were detected optically as a function of the applied bias. It was found that a hole injecting layer, consisting of 3,4 polyethylene-dioxy-thiophene doped with polystyrenesulfonate, forms an ohmic contact to the HTL by inducing a thin layer of holes in the interfacial region. An analytical model is developed to describe the observed carrier concentrations as well as the current–brightness–voltage characteristics quantitatively. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 1886-1892 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: An analytic theory has been developed to analyze the rise of electroluminescence from bilayer light emitting diodes upon applying a rectangular voltage pulse if the current of majority carriers is space charge limited while minority carrier injection is electrode limited. The onset of electroluminescence is governed by the growth of the interfacial charge densities rather than by the transit time. This result suggests that, for appropriate interfacial energy barriers, balanced injection can be established even if only one of the electrodes is ohmic. A qualitative agreement between theory and experiment has been obtained. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2961-2967 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Spectral, field, and temperature dependencies of steady-state photoconductivity were studied in thin films of pure phenyl substituted copolymeric polyphenylenevinylene (PhPPV) and PhPPV doped by trinitrofluorenone. The films were sandwiched between indium tin oxide (ITO) and aluminum as well as between two aluminum contacts. Typical surface extrinsic carrier photogeneration was observed in ITO/PhPPV/Al samples with positively biased ITO while the intrinsic photoconductivity dominated in Al/PhPPV/Al samples and ITO/PhPPV/Al sandwiches with negatively biased ITO. Charge carrier photogeneration in both doped and undoped PhPPV at higher photon excess energies was found to be in good agreement with predictions of the hot exciton dissociation model. At low excess photon energy of the inducing light, carrier photogeneration is ascribed to dissociation of optical excitations on charge transfer centers which are either dopant molecules in the doped samples or intrinsic defects in the pure material. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 10007-10013 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We report on measurements of phosphorescence (Ph) and delayed fluorescence (DF) in poly(2,7-(9,9-bis(2-ethylhexyl)fluorene)) (PF2/6) present as dilute solid solution, as well as in bulk films. From combined experimental investigations of the time and intensity dependence of DF and Ph, as well as the temperature dependence of DF, we are able to show that DF in PF2/6, both in solution and film, is dominated by triplet-triplet annihilation (TTA). As a consequence of the intrachain diffusion and, hence, relaxation of triplets, the kinetics of the bimolecular reaction show a turnover from dispersive to nondispersive regime as borne out by the DF decay. This is in accord with theoretical predictions of TTA in disordered solids. From the transition to equilibrium kinetics, we are able to estimate the width of the density of states of triplets to 40 meV in good agreement with the width of the inhomogeneous broadenend S0←T1 transition of PF2/6. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 2758-2760 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A tandem mechanism of charge injection from a metal contact into an organic dielectric via an intermediate injection-facilitating layer is considered. It is shown that introducing such a layer can enhance charge injection considerably if the energy of transport states in this layer is in between the Fermi level of the contact and the energy of transport states in the bulk dielectric. The optimum energy of transport states in the intermediate layer and the minimum thickness thereof are calculated. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Oxford, UK and Malden, USA : Blackwell Science Ltd
    BJOG 111 (2004), S. 0 
    ISSN: 1471-0528
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: The aim was to assess symptoms of pelvic floor dysfunction in women following pelvic trauma. A retrospective questionnaire survey of 24 consecutive women was performed in a tertiary referral orthopaedic centre and urogynaecology unit. Sixteen women had a type B and eight a type C pelvic fracture (Association Osteosynthesis manual classification). The median age was 24 years (11–92). Twenty-one women were nulliparous. Sixteen women reported de novo pelvic floor dysfunction. Bladder symptoms occurred in 12, bowel problems in 11 and sexual dysfunction in 7 of 17 sexually active women. Pelvic fracture seems to be a risk factor for pelvic floor dysfunction.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Pacing and clinical electrophysiology 23 (2000), S. 0 
    ISSN: 1540-8159
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: This study prospectively examined the role of cognitive behavioral therapy (CBT) in (1) alleviating psychological and somatic distress, and (2) lowering arrhythmic events requiring shocks. Forty-nine of 61 consecutive patients were randomized into therapy (CBT, n = 25) or no therapy (NT. n = 24) and completed a battery of self-report questionnaires at baseline and at 9-month follow-up. CBT was administered at preimplant, predischarge, and at seven routine follow-up visits. Patients were 65 ± 10 years old. 65% were men, and 92% Caucasian. Eighteen (72%) CBT patients and 18 (75%) NT patients were retained at follow-up. Compared to CBT patients, NT patients reported higher levels of depression (P = 0.046), more anxiety (P = 0.013), more psychological distress (P = 0.015), poorer overall adjustment (P = 0.009), and poorer sexual functioning (P = 0.003). Mean number of shocks did not differ between the CBT and NT groups (2.85 vs 2.30. respectively); however, more patients in the CBT group (61%) than the NT group (33%) received shocks (P = 0.070). At follow-up, a subgroup analysis revealed that the significant differences observed between the CBT and NT groups were attributable to the patients who received shocks in both groups. In conclusion, CBT was associated with decreased depression, decreased anxiety, and increased adjustment for ICD recipients, particularly among those patients receiving shocks. CBT can be administered effectively at routine follow-up visits or transtelephonically with little added inconvenience to the ICD recipient.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 3802-3807 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Employing the time-of-flight (TOF) technique, the hole mobility in films of polyphenylenevinylene-ether has been measured as a function of electric field and temperature. Charge carriers were generated upon either photoexcitation into the S1←S0 transition of the polymer or via sensitized injection from a thin rhodamine 6G layer. The results will be interpreted in terms of the concept of hopping among polymer segments featuring a Gaussian distribution of energies, its variance being 91 meV. While TOF signals generated via sensitized injection are similar to those in molecularly doped polymers bearing out a transition from nondispersive to dispersive transport, intrinsically generated TOF signal features a cusp at higher temperature and almost no dispersion. The latter phenomenon turns out to be a consequence of charge generation at the tail of the density distribution of hopping states. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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