Time-of-Flight Current Shapes in Molecularly Doped Polymers: Effects of Sample Thickness and Irradiation Side and Carrier Generation Width
ABSTRACT: The time-of-flight (TOF) current transients from solution-cast, free-standing films of p-diethylaminobenzaldehyde diphenyhydrazone in bisphenol A polycarbonate (DEH:PC) have been studied using electron gun induced charge generation. Changes in the shape of the current transient, cusp formation in particular, with film thickness, electron-beam penetration depth, and the side of the sample irradiated, have been analyzed with a two-layer multiple trapping model, and indicate that the time-of-flight transients of solution-cast films can be problematic in that plateau formation does not necessarily imply nondispersive charge transport. The results are consistent with the existence of thin surface layers which are depleted of the hole transport material. The depleted layer on the surface of the film that was exposed to air during coating/drying is always thicker than it is for the surface contacting the substrate. Depletion could occur through transport material sublimation, surface physical characteristics such as porosity, inhomogeneous solvent evaporation, or some other mechanism.
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.
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.
By using superconducting quantum interference device (SQUID) magnetometry, we investigated anisotropic high-field (H less than or similar to 7T) low-temperature (10 K) magnetization response of inhomogeneous nanoisland FeNi films grown by rf sputtering deposition on Sitall (TiO2) glass substrates. In the grown FeNi films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the percolation transition at the d(c) similar or equal to 1.8 nm. We discovered that, beyond conventional spin-magnetism of Fe21Ni79 permalloy, the extracted out-of-plane magnetization response of the nanoisland FeNi films is not saturated in the range of investigated magnetic fields and exhibits paramagnetic-like behavior. We found that the anomalous out-of-plane magnetization response exhibits an escalating slope with increase in the nominal film thickness from 0.6 to 1.1 nm, however, it decreases with further increase in the film thickness, and then practically vanishes on approaching the FeNi film percolation threshold. At the same time, the in-plane response demonstrates saturation behavior above 1.5-2T, competing with anomalously large diamagnetic-like response, which becomes pronounced at high magnetic fields. It is possible that the supported-metal interaction leads to the creation of a thin charge-transfer (CT) layer and a Schottky barrier at the FeNi film/Sitall (TiO2) interface. Then, in the system with nanoscale circular domains, the observed anomalous paramagnetic-like magnetization response can be associated with a large orbital moment of the localized electrons. In addition, the inhomogeneous nanoisland FeNi films can possess spontaneous ordering of toroidal moments, which can be either of orbital or spin origin. The system with toroidal inhomogeneity can lead to anomalously strong diamagnetic-like response. The observed magnetization response is determined by the interplay between the paramagnetic-and diamagnetic-like contributions.
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.