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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 7598-7605 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A model is developed that describes bimolecular recombination of photogenerated carriers in two dimensional systems. Carriers are free to diffuse in two dimensions and undergo bimolecular recombination, while drifting under the influence of an electric field in the third dimension. The model describes a competition between carrier loss due to transiting and loss due to bimolecular recombination. This model of recombination quenching is then used to obtain information on microscopic parameters associated with photogeneration efficiency and charge transport in organic quantum wells formed from Langmuir Blodgett films of conjugated molecules. The ratio of the intralayer to interlayer tunneling rates is found along with the quantum efficiency for photocarrier generation for two bis-phthalocyanine amphiphilic molecules. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 7606-7612 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The tunneling rate of photocreated charge carriers between layers in Langmuir–Blodgett multilayer structures is measured indirectly using the novel technique of bimolecular recombination quenching. The tunneling rate is demonstrated to be dependent upon the applied electrostatic potential difference between the layers. This dependence is explored in light of the Marcus theory of charge transfer. That theory was developed to describe redox reactions where the driving force is supplied by a chemical potential difference between two chemically different parts of a more complex system. In the current work the electrostatic potential replaces the chemical potential as the driving potential. The field dependence of the exciton dissociation probability is also determined. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 7613-7620 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The tunneling rate of photocreated charge carriers between layers in Langmuir–Blodgett multilayer structures is measured indirectly using the novel technique of bimolecular recombination quenching. The tunneling rate is measured as a function of the applied electrostatic potential difference between the layers as the temperature is varied between 300 and 4 K. This dependence is examined in light of the Marcus theory of charge transfer where the electrostatic potential replaces the chemical potential as the driving potential. The expectations of the Marcus theory are not met and the rate is effectively temperature independent, contrary to expectation. Other mechanisms are explored that may explain the lack of temperature dependence including the role of high frequency vibrations and the role of the zero point energy of those vibrations. The temperature dependence of the exciton dissociation probability is also examined. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 10400-10408 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A study of charge transport in the crystalline phase of the columnar liquid crystal, hexakis(n-hexyloxy)triphenylene, HAT6, is reported. A simple model is introduced and fitted to observations of photocurrent transient decays in the crystalline phase of HAT6. From these a quasi one-dimensional trapping process is inferred with a field dependent trapping rate determined by carrier drift at high fields and controlled by carrier diffusion in the limit of zero field. The detrapping rate is found to be independent of field indicative of a neutral barrier. The trap concentration is found from fits of the transients to the model. The mobility of holes in the crystalline phase is found and compared to the time-of-flight mobility previously found for HAT6 in the discotic mesophase. Also found is the field dependence of the generation rate in the presence of an absorbing electrode adjacent to the photocreation site. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 918-923 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The attempts to create thinner samples of columnar discotic liquid crystals in order to avoid stack defects and measure charge carrier motion on low defect density stacks by the time of flight technique, inevitably leads to problems. The time of flight becomes faster while the electronic response time becomes slower as a result of the increasing sample capacitance. Eventually the time of flight transit time becomes indiscernible due to the system response distortion. This article demonstrates the recovery of the time of flight signal from such distorted data by analyzing the nature of the signal and using this analysis to deconvolve a digitally acquired signal. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 914-924 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Intermolecular photoelectron transfer in a vector ordered molecular assembly, produced as a Langmuir–Blodgett multilayer, causes currents and voltage changes at electrodes. A comprehensive account is given of the experimental determination of the voltage changes, which can be done, in principal, with a time resolution of 25 ps. The present experimental limitations to this time resolution are described. The experiments allow determination of the time evolution of the charge-separation product. The means of determining the intermolecular transfer time of the carriers in such multilayers is described. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1472-1476 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The range of carriers in thin crystalline films of the conjugated polydiacetylene derivatives 3 and 4BCMU [with the side groups R1=R2=–(CH2)3–OCO–NH–CH2–COOC4H9 and –(CH2)4–OCO–NH–CH2–COOC4H9] are demonstrated to be greater than 110 and 90 μm, respectively, and the quantum efficiencies for carrier generation are determined. The films are created as a result of electron-beam-induced topochemical polymerization of a thin surface layer on a crystalline monomer substrate. The polymer films are subsequently separated from the underlying monomer and deposited onto a series of interdigitated electrodes with varying interelectrode separation. The range and generation efficiencies are deduced by measuring the photocharge induced on the electrode system as a result of a laser pulse. Comparisons are made with bulk single crystals. © 1999 American Institute of Physics.
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  • 8
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1797-1802 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Experimental measurements are presented of the hole mobilities of four conjugated discotic systems, forming columnar liquid crystals, as a function of temperature. The measurements cover the crystalline/glassy phase and mesophase of these materials. It is a remarkable fact that the mobility is almost independent of temperature in the range 30 °C–170 °C. Various explanations of a weak temperature dependence exist and these are explored. They include the small polaron of Holstein in the nonadiabatic limit and the effect of the dynamic disorder present in the system. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    European journal of applied physiology 80 (1999), S. 107-112 
    ISSN: 1439-6327
    Schlagwort(e): Key words Fire-fighting ; Self-contained breathing apparatus ; Laboratory-based tests ; Ventilatory responses
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract In the present study we compared the ventilatory performance whilst wearing self-contained breathing apparatus (SCBA) during exercise, of a group of male fire-fighters (FF, n = 8), with a matched group of male civilians (CV, n = 7). The mean (SEM) physiological characteristics of the subjects (FF vs CV) were: age 31 (2) years vs 32 (4) years; height 179 (2) cm vs 183 (3) cm, P 〈 0.05; mass 80 (2) kg vs 84 (3) kg; maximum oxygen uptake 4.52 (0.14) l · min−1 vs 4.39 (0.27) l · min−1. Volunteers performed a 23-minute fire-fighting simulation (Firetest), without and with SCBA (Fire-fighter II, Siebe-Gorman/North Safety, Cheshire, UK). During SCBA wear, the FF group used significantly less air and rated their breathlessness significantly lower than the CV group. The mean tidal volume (V T) of the FF group remained constant between non-SCBA and SCBA wear conditions, but the CV group increased their mean V T by 18%, (P 〈 0.01). There were no significant between-group differences during the Firetest in total breath duration, inspiratory or expiratory duration, breathing frequency ( f b), or heart rate. These data suggest that the respiratory responses of firefighters while wearing SCBA, which are characterised by increases in ( f b) but not V T, may help to reduce their breathlessness during exercise while wearing SCBA.
    Materialart: Digitale Medien
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