Тютнев Андрей Павлович

Time-Resolved Radiation-Induced Conductivity of Polyimide and Its Description Using the Multiple Trapping Formalism

2019 · ARTICLE · en

Abstract: Polymer dielectrics subjected to intense radiation fluxes exhibit a radiation-induced conductivity (RIC). Polyimide is a good dielectric with excellent mechanical and thermal properties featuring high radiation resistance currently widely used in the spacecraft industry. Its RIC has been extensively studied in several laboratories. The purpose of the present study is to make a direct measurement of the RIC for both pulsed and continuous irradiation using a current sensing technique, which is contrary to the indirect method employing a surface-potential decay technique that is now preferred by spacecraft charging engineers. Our experiments are done in a small-signal regime excluding any recombination and dose e ects. In combination with existing computer codes, we managed to develop further the conventional multiple trapping formalism and the RIC theory based on it. The main idea is to supplement an exponential trap distribution responsible for a dominant dispersive carrier transport in polymers with a small concentration of inherent deep traps which may or may not have an energy distribution. In line with this reasoning, we propose a tentative set of RIC model parameters for polyimide that accounts for the observed experimental data. The findings and their implications are discussed in a broad context of previous studies.

Numerical analysis of the photo-injection time-of-flight curves in molecularly doped polymers

2018 · ARTICLE · en

We have performed numerical analysis of the charge carrier transport in a specific molecularly doped polymer using the multiple trapping model. The computations covered a wide range of applied electric fields, temperatures and most importantly, of the initial energies of photo injected one-sign carriers (in our case, holes). Special attention has been given to comparison of time of flight curves measured by the photo-injection and radiation-induced techniques which has led to a problematic situation concerning an interpretation of the experimental data. Computational results have been compared with both analytical and experimental results available in literature.

Frequency Factor of the Semiempirical Model for the Radiation-Induced Conductivity in Spacecraft Polymers

2018 · ARTICLE · en

Present-Day Status of Spacecraft Charging Investigations in Russia

2018 · CHAPTER · en

Currently, Russia conducts various works aimed at mitigating spacecraft charging effects interfering with the operation of the on-board electronics. We will inform you about the progress in developing the discharge-free near- Earth satellites. Also, we will report on participation of our specialists in preparing international guidance documents on the problem of spacecraft charging. A part of this paper will cover spacecraft activities investigating geomagnetic and radiation conditions on near-Earth orbits

Poole-Frenkel mobility field dependence in molecularly doped polymers revisited

2017 · ARTICLE · en

We have examined the Poole-Frenkel mobility field dependence in a molecularly doped polymer (MDP) both experimentally and theoretically trying to separate two physically different contributions to this phenomenon, one constituting a real physical effect and the other arising from the fact that the charge carrier transport in MDP is not fully equilibrated. The former is ascribed to the influence of an electric field on the transport process itself affecting at least one of the model parameters. The latter should be associated with the mobility field effect under conditions when neither model parameter is field sensitive. Numerical calculations have been used to achieve their deconvolution. On the experimental front, we relied on the time of flight technique specifically modified to suit this task. Both approaches show that the contribution of the second (operational) field effect in the investigated MDP is quite appreciable. This result is compared with the traditional interpretation of the Poole-Frenkel effect in molecularly doped polymers.

The Nature of Plateau on Time-of-Flight Curves in Molecularly Doped Polymers

2017 · ARTICLE · en

Сопоставлены кривые переходного тока в полярном молекулярно допированном полимере для приповерхностной и объемной генерации носителей заряда. Ожидаемого в условиях квазиравно- весного транспорта превращения горизонтального плато на первой из них в кривую, предсказыва- емую теорией диффузии и дрейфа, не произошло. Такое поведение свидетельствует о неравновес- ном характере транспорта носителей заряда. Появление плато в нашем случае объясняется влияни- ем обедненного приповерхностного слоя, как на это мы уже указывали ранее.

Computer Simulations and Experimental Verification of the Nanoconductivity Concept for the Spacecraft Electronics

2017 · ARTICLE · en

Abstract—This paper develops the concept of the nanoconductivity of insulators as applied to the space technology aimed at creating discharge-free space vehicles and discusses the ways to achieve this. Feasibility analysis of advanced, next generation, discharge-free satellites widely using nanoconducting insulators in spacecraft electronics proves that such a transition is not only necessary but is also practicable. We have performed computer simulations of a multivibrator, which is a typical representative of the digital technology, using the LTspice software. As any spacecraft dielectric is a potential source of the electrostatic discharges, it is advisable to implement the nanoconductivity concept by replacing high-resistivity insulators with the nanoconducting dielectrics featuring electrical conductivity around 10^−9 Ohm^ −1m^−1.

About mobility thickness dependence in molecularly doped polymers

2017 · ARTICLE · en

We have investigated the dependence of hole mobility on thickness in free-standing films of bisphenol-Apolycarbonate (PC) doped with 30 wt% p-diethylaminobenzaldehyde diphenylhydrazone (DEH). Carrier generation in a time-of-flight (TOF) experiment was achieved through direct ionization of dopant molecules by electron impact using an electron gun supplying pulses of monoenergetic electrons in the range of 2–50 keV. The position of dopant ionization depends upon the electron energy and three TOF variants have been recently developed and used in this study. We have found that the hole mobility generally decreased with increasing film thickness with concomitant acceleration of the post-flight current decay indicating that the transport process approaches the steady-state regime, this process happening slightly faster than our model predicts. Numerical calculations have been compared with experimental data. The results are discussed in detail. The way to reconcile ostensibly contradictory interpretations of our results and those commonly reported in literature relying on photo injection technique has been proposed.

Comparative Monte-Carlo simulations of charge carrier transport in amorphous molecular solids as given by three most common models of disorder: The dipolar glass, the Gaussian disorder, and their mix

2017 · ARTICLE · en

We have performed Monte-Carlo simulations of the charge carrier transport in a model molecularly doped polymer using three most popular hopping theories (the dipolar glass model, the Gaussian disorder model, and an intermediate between them) in a wide range of applied electric fields and temperatures. Time of flight transients have been computed and analyzed in logarithmic coordinates to study the Poole-Frenkel field dependence, the non-Arrhenius mobility temperature dependence, and the nondispersive versus dispersive current shapes. We also have made an attempt to estimate the total disorder energy directly from simulation data at the lowest electric field thus checking the consistency of the model fitting. Computational results have been compared with the analytical and experimental information available in the literature.

Analytic Modeling of Field Dependence of Charge Mobility and Applicability of the Concept of the Effective Transport Level to an Organic Dipole Glass

2017 · ARTICLE · en

An analytic model for the field dependence of charge mobility is developed within the long-range-correlated disorder model of a dipole glass. Release of a charge carrier from a deep state is considered as hopping drift and diffusion in a quasi-Coulomb potential well. The analytic results, containing only one numerical parameter obtained from independent simulation, are in good agreement with the fit to the Monte-Carlo simulations. The developed approach justifies applicability of the concept of the effective transport level for the modeling of organic materials with large molecular dipoles.