Trapping events

A representative example for the information extracted from a TRMC experiment is the work of Prins et al. [141] on the electron and hole dynamics on isolated chains of solution-processable poly(thienylenevinylene) (PTV) derivatives in dilute solution. The mobility of both electrons and holes as well as the kinetics of their bimolecular recombination have been monitored by a 34-GHz microwave field. It was found that at room temperature both electrons and holes have high intrachain mobilities of fi = 0.23 0.04 cm A s and = 0.38 0.02 cm / V s V The electrons become trapped at defects or impurities within 4 ps while no trapping was observed for holes. The essential results are (1) that the trap-free mobilities of electrons and holes are comparable and (2) that the intra-chain hole mobility in PTV is about three orders of magnitude larger than the macroscopic hole mobility measured in PTV devices [142]. This proves that the mobilities inferred from ToF and FET experiments are limited by inter-chain hopping, in addition to possible trapping events. It also confirms the notion that there is no reason why electron and hole mobilities should be principally different. The fact... 

A single ionization event creates a hole and an ejected electron. To maintain charge neutrality, if a hole is trapped, then an electron is also trapped. Therefore the radical yield must consist of equal oxidation (e removal) and reduction (e trapping) events. The electron addition half occurs exclusively at the bases, while the electron loss half occurs according to the number of electrons per component. That means 52% of the holes are initially generated on the sugar phosphate, corresponding to 26% of the initial radicals. A... 

Let us define the (multiple) trapping events. As mentioned before, trapping describes the occasional immobilization of the random walking test particle... 

This model for subdiffusion in the external force field F(x) — — ( ) provides a basis for fractional evolution equations, starting from Langevin dynamics that is combined with long-tailed trapping events possessing a... 

With the experimental results in mind we retium to the analysis of the trap-limited transport. The time-dependent decrease in the apparent mobility is obviously consistent with our earlier argument that the average trapping time will increase with the number of trapping events for an exponential band tail. Scher and Montroll (1975) were the first to point out this property of a very broad distribution of release times and to associate the effect with transport in disordered semiconductors. They analyzed the random walk of carriers with such a distribution and... 

This analogy between the motion of electronic carriers and of hydrogen cannot be taken very far because the hydrogen diffusion has some added complications. Dispersive diffusion of electrons or holes occurs with a low density of carriers in a large density of traps and the trapping events are largely independent. Hydrogen diffusion takes... 

When shallow Coulomb trapping centers are introduced into the bulk of a silver halide crystal, the electron is presumed to spend some time in the conduction band and some time in the shallow traps. If the electron is lost only out of the conduction band and no other loss processes are introduced, then the time before final trapping is lengthened by the time spent in the shallow traps. The number of trapping events (Z) during an electron s free time (<) in the conduction band is given by... 

We have divided the following discussion into three sections according to whether carrier trapping processes are dominated by (1) shallow trapping, (2) self-trapping events in the perfect lattice or at sites associated with lattice disorder, or (3) trapping in deep levels. 

Having shown that the intramolecular Wessely oxidation approach was possible, although very poor yielding, we wondered if a faster intramolecular trapping event would ensure a more successful dearomatization outcome. 

Scheme 6.10 HDDA reaction followed by an intramolecular silyl ether trapping event.

We have performed a QNS study over a wide dynamical range on the H diffusion in amorphous P gQSi20 most prominent result is the discovery of two distinctly separated regimes of jump rates instead of the expected continous distribution. From our model-independent data evaluation we get reasonable H diffusion coefficients and we derived that the fast H motion is spatially restricted to regions of about 10 X diameter. From the temperature dependence of the weight of the broad component we conclude that the fast localized motion is due to thermal activation from a trapped state and not to back-and-forth hopping in extended traps. A satisfactory description of the QNS data is possible in the framework of a two-state-model for amorphous Pdg Si Q in which fast local H diffusion is interrupted frequently by trapping events. 

By calculating the total niunber of trapping events it can be seen that the typical distance which a charge carrier travels between two trapping events is of the order of 4 A. This value is comparable to the intrachain distance and indicates that the transport in these materials can be best described by conventional hopping between closely neighbouring sites. No evidence for bandlike transport has been foimd. 

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