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Three dimensional dielectric systems are simulated to obtain the relaxational polarization responses. The dielectric system consists of randomly distributed permanent dipoles that fluctuate due to thermal activation in double well potentials between two plane-parallel electrodes. The barrier height between the wells is assumed to be proportional to the dipole length. The electrodes' effect is considered with the method of images. The relaxational phenomena of two dielectric systems, one with fixed and the other with distributed dipole lengths having single and distributed relaxation times, respectively, are calculated with a Monte-Carlo simulation method. The local field at every dipole and consequently the transition probabilities are computed to determine the transient polarization response iteratively. Both dielectric systems are simulated over a wide range of temperatures for interacting and non-interacting cases. The mean relaxation times exhibit a Vogel-Fulcher law for interacting systems and an Arrhenius law for non-interacting systems. [ABSTRACT FROM AUTHOR]

Metal-aluminum oxide-metal structures are prepared by evaporation in vacuum on silicon wafers using Au, Cu or Pd on top and Al as bottom electrode. The aluminum oxide layer is deposited by electron beam evaporation with a thickness of 200 nm. The diameter of the top electrode is varied between 0.1 and 1.9 mm. Capacitance measurements reveal a relaxational dielectric permittivity as expected for aluminum oxide. Applying ramp voltages results in single breakdown spots on the electrode before the structure finally becomes conductive. The breakdown spots, as characterized with an AFM, are in the form a crater, reaching 500 nm into the silicon. However, for the smallest electrode, the calculated electrostatic energy stored in the capacitance is not high enough to form the craters. [ABSTRACT FROM AUTHOR]

The understanding of the complexity of the space charge formation and movement inside insulation materials demands a high resolution measurement technique. The Kelvin Probe Force Microscopy (KPFM) can fulfill this demand. The KPFM delivers the data of the locally varying surface potential. They can be differentiated twice together with a reliable statistical approach to overcome the noise problem in the experimental surface potential data. In this way, we get the locally varying space charges according to the Poisson equation. This statistical approach has been tested by comparing the calculated space charge distributions from simulated and measured noisy surface potential data. The formation and the movement of space charges with respect to time under unbiased and biased conditions were investigated. [ABSTRACT FROM PUBLISHER]

In this Special Issue of IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION (TDEI) on Electrets and Related Phenomena, we have assembled a total of 14 invited and contributed papers that were mostly presented at the IEEE 18th International Symposium on Electrets (ISE18). ISE is the premier IEEE-sponsored conference on electrets under the auspices of the IEEE Dielectrics and Electrical Insulation Society (DEIS) since 1985. Its predecessors had been held since 1967 under different umbrellas such as the Electro-Chemical Society (ECS), as well as Brazilian and Japanese scientific organizations. The ISE symposia provide a unique meeting opportunity for scientists and engineers from all over the world working in the field of condensed-matter physics and chemistry, electrical engineering and materials science. ISE18 was held on September 24–28, 2021, and hosted by Tongji University, with additional support from the Electrostatics Committee of the Chinese Society of Physics, the Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, the Chinese Academy of Sciences–Shenzhen Institutes of Advanced Technology, Fudan University, and the East China University of Science and Technology. [ABSTRACT FROM AUTHOR]

Previously an asymmetric double well potential model was successfully applied to interpret the nonlinear relaxational polarization of Al2O3. Here we extend this model to HfO2. The capacitance measurements on HfO2 based metal-insulator-metal MIM capacitors were performed. To study this relaxational polarization the thickness of the dielectric, device temperature, frequency and electric field were varied systematically. It was revealed that at lower temperatures T ⩽ 180 K the relaxation happens via proton tunneling transition in asymmetric double wells. Incorporation of protons in HfO2 is illustrated by monitoring the mass spectra during oxide evaporation. Above 180 K the thermal activation transition comes in a play but the relaxation process is also found to be influenced by electrode space charges. One of our goals here was to show that our model is not specific to Al2O3 and it has the ability to explain the nonlinearity of other metal oxides. [ABSTRACT FROM AUTHOR]

The non-exponential polarization and depolarization current density after a voltage step is investigated in the ion conducting polymer polyethylene oxide yielding a Kohlrausch or Curie-von Schweidler behavior in the long and in the short time range with different exponents respectively. To explain this behavior simulations with a three-dimensional hopping model are performed. Interactions between all charges in the system are considered. A distribution of sites is introduced to construct an amorphous structure. The intrinsic barrier heights between two neighboring sites in a multi-well energy structure depend here on the distance between the sites and the interaction between the charges yielding a distribution of relaxation times. Simulations with this model show a Kohlrausch behavior in the long time range as well as in the short time range. For short times the distribution of relaxation times is responsible for the Kohlrausch behavior. In the long time range a distribution of distances of the sites to the electrodes resulting in a distribution of image forces causes the Kohlrausch current. [ABSTRACT FROM AUTHOR]

The polarization and the depolarization current after application of a voltage step are investigated in the solid electrolyte polyethylene oxide. For low applied fields the current density follows a Kohlrausch behavior, i.e. j α f?, in the long time range during the polarization and the depolarization process respectively. By using sufficiently high applied fields charge injection sets in and the current during the polarization process is nearly constant at long times. It turns out that the transient depolarization current in this case shows a pronounced unforeseen maximum. The time to the maximum as well as the height of the current peak depend on the field applied before, the polarization time, the temperature, the LiClO4 doping, the electrode material, and the sample length. Simulations carried out using a discrete three-dimensional hopping model reveal qualitatively comparable results. It is concluded that the injection and later extraction of excess electrons accordi [ABSTRACT FROM AUTHOR]

The surface of silicondioxide/silicon structures is charged with the tip of a cantilever in contact mode by application of a voltage. Then, the surface potential is measured contactless using the Kelvin option of an atomic force microscope. On the position of the charged domain a potential difference in relation to the uncharged region is found. It turns out that the height and the width of this potential difference depend on the charging time, on the height of the charging voltage, on the sample thickness, and on the doping of the siliconsubstrate. Furthermore, a time dependent spread and a decay of the surface potential are observed. For dry samples the decay is slower than for wetted samples. Due to this long-term stability at dry samples and the possibility to reverse the sign of the deposited charge by recharging in opposite direction it is thinkable to use the system as a surface charge memory device. [ABSTRACT FROM PUBLISHER]

Using the scanning Kelvin probe the potential distribution on the surface of an ion-conducting polymer (polyethylene oxide) can be determined. Due to space charge accumulations a voltage applied between two electrodes causes a strongly nonlinear potential distribution in the samples. The curvature of the potential distribution indicates negative mobile ions in the samples. During the measurement the dc currents in the samples are observed to verify the steady state of the potential distribution. Additionally the measurement results are compared to simulations performed with a three-dimensional hopping model. These simulations show qualitatively the same results as the experiments. [ABSTRACT FROM AUTHOR]

We are pleased to announce that the June 2022 issue of the IEEE Transactions on Dielectrics and Electrical Insulation (TDEI) will be a special issue on electrets and related phenomena. This issue is open to all authors. Presenters of papers at the IEEE 18th International Symposium on Electrets (ISE18) to be held during September 24–28, 2021 in Shanghai (China) are especially encouraged to submit their work to this special issue. For more information on ISE18 please go to https://ise18.tongji.edu.cn/. [ABSTRACT FROM AUTHOR]

Numerical simulations of the properties of dielectric nanocomposites using local field calculations are performed. Thus the dipole-dipole interactions and interactions between the dipoles and the electrodes are considered. The simulations are based on the microscopic local field method and a dynamic Monte Carlo algorithm. In the context of dielectric binary mixtures no analytic solution exists for a given microstructure. Such a problem can only be solved numerically. The approximations for such a system using macroscopic mixing rules can be misleading. We compare the results obtained by the local field method to the classical mixing rules of Maxwell-Garnett and Polder-van Santen. In the context of a polar guest phase in a non-polar host phase the impact of the nanodielectric inclusion modeled by permanent dipoles into the host matrix is investigated. For a two phase system with polar and non-polar units we simulate all interactions and investigate the ferroelectric hysteresis. The ferroelectric hysteresis is observed for the modeled P(VDF/TrFE) structure with dielectric layers on both sides. We will see that many effects which are unique for a given microstructure can not be observed by the application of a strategy of homogenization which is the case for all empirical mixing rules. [ABSTRACT FROM PUBLISHER]