The Nature of Plateau on Time-of-Flight Curves in Molecularly Doped Polymers
Abstract—Transient current curves in a polar molecularly doped polymer for subsurface and bulk generations of charge carriers are compared. No transformation of the horizontal plateau on the former to the curve predicted by the diffusion and drift theory was found, contrary to expectations for quasi-equilibrium transport conditions. This behavior indicates a nonequilibrium character of the transport of charge carriers. The plateau appearance is explained in our case by the depleted subsurface layer effect, as we already pointed out earlier.
ABSTRACT: The time-of-flight (TOF) transients of solution-cast, free-standing films of N,N′-diphenyl-N,N-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′diamine (TPD) in bisphenol A polycarbonate (PC) have been studied using electron gun induced charge generation. This molecularly doped polymer (MDP) has been shown to exhibit perfectly flat plateaus on its time-of-flight curves with optical excitation. Our TOF results with continuously changing electron energies, as well as numerical calculations using a multiple trapping model with a Gaussian trap distribution (MTMg), suggest that charge carrier transport in this molecularly doped polymer is nonequilibrium and the flat plateaus can be explained by the presence of a thin surface layer depleted of transport material. The depleted surface layers on samples of this molecularly doped polymer are extremely thin (less than 0.12 μm), with those relating to the release side (contacting a substrate during coating/drying procedure) being much smaller than for the free side exposed to air. Since TPD-doped PC and a tetraphenylbenzidine polymer containing the TPD moiety in its main chain served as the prototype materials for the concept of “trap-free” carrier transport, we have also discussed this in detail.
We have compared time-of-flight curves predicted by hopping and multiple trapping models with the Gaussian and exponential site/trap energy distributions, fitting Monte-Carlo predictions of the former with numerical calculations of the latter in a wide time domain using logarithmic coordinates lg j–lg t for the characterization of current shapes and an estimation of transit times. As a prototype hopping theory, we used the Gaussian disorder model while for representing the quasi-band theories we relied on the multiple trapping model, both of these for two types of the site/trap energy distributions. In case of the Gaussian distribution of trap depths, fitting procedure requires adjusting of the two model parameters (an energy distribution parameter σ and a frequency factor ν0). For an exponential distribution, a one-parameter (ν0) fitting suffices. The dipolar glass model, unlike the Gaussian disorder model, is basically different from the multiple trapping formalism, but a recently introduced two-layer multiple trapping model seems capable of reproducing TOF current shapes rather well.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.