Limiting-current measurement transition times

For times less than the transit time of the wave, the current is proportional to the stress at the input electrode in a linear approximation. For times greater than the wave transit time, the current is proportional to the stress difference between the electrodes. Thus, the thin-film nature of PVDF provides a means to measure stress differences, and, given mechanical tolerances that limit loading times to a few nanoseconds, measurements are difficult to... 

Two main methods have been used to measure the charge carrier mobility in electroluminescent polymers time of flight (TOF) carrier transit time measurements and analysis of the current-voltage (1-V) characteristics of single carrier devices in the space charge-limited current (SCLC) regime. A summary of the results for the hole mobility of PPV and PPV-related polymers is given in Table 11-1 [24, 27-32]. For... 

When time-dependent signals are to be measured by a photomultiplier, the time sensitivity is usually limited by the inhomogeneous transit time. The transit time is the time taken by electrons generated in the cathode to arrive at the anode. If all of the emitted electrons had the same transit time, then the current induced in the anode would display the same time dependence as the incoming light, but delayed in time. However, not all of the electrons have the same transit time. This produces some uncertainty in the time taken by electrons to arrive at the anode. There are two main causes of this dispersion ... 

Unambiguous steady-state measurements are carried out only in the trap-free space-charge-limited-current (SCLC) regime (23), when the average transit time (f j of any excess injected carrier across the sample bulk is shorter than the time required for the bulk to locally neutralize the carrier (22). The transit time ( r) has been defined in equation 1. The time to neutralize any excess injected carrier is the bulk dielectric relaxation time, Tr ( r = in which p is the bulk resistivity and e is the bulk dielectric... 

Finally, in recent unpublished work, Louge and Hanson (1981) carried out a limited series of incident shock wave experiments in N2 0/Ar mixtures and inferred k by comparing N2O time histories measured by ir emission (4.5 fim) with those computed using a detailed kinetic model. The effects of shock attenuation, boundary layers, finite electronic response and shock transit times, and fall-off were all analyzed, and small corrections were applied where necessary. Their results also agree well with the current recommendation for ki. 

Extending the current state of knowledge could involve measurements at high temperature with shock experiments to access transition pressures closer to the thermodynamic limit. Progress is currently being made to study the transition in individual nanocrystal particles, to both eliminate the ensemble statistics and allow for individual transitions to be observed on -femtosecond time scales. The study of nanocrystal solid-solid phase transitions to oxide nanosystems should also prove to be useful in understanding the microscopic process of solid-solid transitions relevant to geophysically important systems. 

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