TY - JOUR A1 - Rychkov, Dmitry A1 - Gerhard, Reimund A1 - Ivanov, Vadim A1 - Rychkov, Andrey T1 - Enhanced electret charge stability on Polyethylene Films treated with Titanium-Tetrachloride vapor JF - IEEE transactions on dielectrics and electrical insulation N2 - Low-density polyethylene (LDPE) films have been treated with titanium-tetrachloride vapor by means of the molecular-layer-deposition method. It is shown that such a treatment leads to a considerable improvement of the electret properties for both positively and negatively charged films. The temperature stability of the electret homo-charge has been increased by approximately 60 degrees C. At the same time, the temporal stability of charge is also considerably improved. Modified low-density polyethylene films show no "cross-over phenomenon" when charged to higher voltages. Thus, it is now possible to produce electrets from polyethylene films with high initial charge densities, but without a strongly reduced charge stability. The influence of a chemical treatment with titanium-tetrachloride vapor on charge injection from aluminum electrodes into polyethylene films was also investigated. It is found that the interface between an aluminum electrode and a modified LDPE surface layer has different injection properties for positive and negative charges. Electrons can be injected across the modified interface, whereas injection of holes is either very limited or non-existent. KW - Electrets KW - chemical modification KW - surface treatment KW - space-charge stability KW - charge-carrier transport KW - polyethylene KW - low-density polyethylene KW - injection Y1 - 2012 SN - 1070-9878 VL - 19 IS - 4 SP - 1305 EP - 1311 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER - TY - GEN A1 - Gerhard, Reimund T1 - Dielectric materials for electro-active (electret) and/or electro-passive (insulation) applications T2 - 2nd International Conference on Electrical Materials and Power Equipment (ICEMPE 2019) N2 - Dielectric materials for electret applications usually have to contain a quasi-permanent space charge or dipole polarization that is stable over large temperature ranges and time periods. For electrical-insulation applications, on the other hand, a quasi-permanent space charge or dipole polarization is usually considered detrimental. In recent years, however, with the advent of high-voltage direct-current (HVDC) transmission and high-voltage capacitors for energy storage, new possibilities are being explored in the area of high-voltage dielectrics. Stable charge trapping (as e.g. found in nano-dielectrics) or large dipole polarizations (as e.g. found in relaxor ferroelectrics and high-permittivity dielectrics) are no longer considered to be necessarily detrimental in electrical-insulation materials. On the other hand, recent developments in electro-electrets (dielectric elastomers), i.e. very soft dielectrics with large actuation strains and high breakdown fields, and in ferroelectrets, i.e. polymers with electrically charged cavities, have resulted in new electret materials that may also be useful for HVDC insulation systems. Furthermore, 2-dimensional (nano-particles on surfaces or interfaces) and 3-dimensional (nano-particles in the bulk) nano-dielectrics have been found to provide very good charge-trapping properties that may not only be used for more stable electrets and ferroelectrets, but also for better HVDC electrical-insulation materials with the possibility to optimize charge-transport and field-gradient behavior. In view of these and other recent developments, a first attempt will be made to review a small selection of electro-active (i.e. electret) and electro-passive (i.e. insulation) dielectrics in direct comparison. Such a comparative approach may lead to synergies in materials concepts and research methods that will benefit both areas. Furthermore, electrets may be very useful for sensing and monitoring applications in electrical-insulation systems, while high-voltage technology is essential for more efficient charging and poling of electret materials. KW - Dielectric materials KW - Electrets KW - Electrical insulation KW - Electro-active and electro-passive dielectrics KW - Nano-dielectrics KW - Charging or poling KW - Charge storage and transport Y1 - 2019 SN - 978-1-5386-8434-4 SN - 978-1-5386-8435-1 U6 - https://doi.org/10.1109/ICEMPE.2019.8727276 SP - 91 EP - 96 PB - IEEE CY - New York ER - TY - JOUR A1 - Rychkov, Dmitry A1 - Gerhard, Reimund A1 - Kuznetsov, Alexey A1 - Rychkov, Andrey T1 - Influence of charge density on the trap energy spectrum in fluoroethylenepropylene copolymer films with chemically modified surfaces JF - IEEE transactions on dielectrics and electrical insulation N2 - Tetrafluoroethylene-hexafluoropropylene copolymer (FEP) films were treated with titanium-tetrachloride vapor by means of molecular-layer deposition. The treatment leads to considerable improvements of the electret-charge stability on positively charged films. A slight improvement is also observed for negatively charged films. In line with our previous findings, we attribute the improvement in electret properties to the formation of deeper traps on the chemically modified polymer surfaces. Here, we investigate the influence of the charge density on electret stability of FEP films with modified surfaces. Trap-energy spectra obtained from thermally-stimulated-discharge measurements indicate that the charge stability on modified FEP films depends on how the surface traps are populated and on the availability of additional deeper traps. KW - Electrets KW - chemical modification KW - surface treatment KW - space-charge stability KW - charge-carrier transport KW - polytetrafluoroethylene (PTFE) KW - fluoroethylenepropylene (FEP) copolymer Y1 - 2018 U6 - https://doi.org/10.1109/TDEI.2018.007437 SN - 1070-9878 SN - 1558-4135 VL - 25 IS - 3 SP - 840 EP - 844 PB - Inst. of Electr. and Electronics Engineers CY - Piscataway ER -