Electric Trapping Research Articles

The Influence of the Ambient Gas Environment on the Non-Isothermal DC Electric Measurements in Polymers

The direct current (dc) electric measurements in dielectrics, especially for highly insulating materials, are strongly influenced by the ambient air, mainly by the water vapors contained by the ambient (humid) air which determine a significant increase of the electric conductivity. Beside this, there is a second effect related to the interaction of the absorbed and adsorbed gas molecules with the polymer matrix that modify both the surface and the bulk conductivities. The aim of the paper is to present the influence of the absorbed and/or adsorbed gas molecules on the electric charge trapping and/or detrapping in polyamide 11. The measurements were carried out under ambient (humid) air, in a vacuum at 8 x 10-3 Torr and in dry nitrogen. Because the trapping/detrapping processes and the molecule diffusion process in polymeric materials are slow processes, a variant of the thermally stimulated discharge current method, namely the final thermally stimulated discharge current method and the final isothermal discharge current method have been used in the temperature range from 20 to 190 0C. The absorbed/adsorbed gas molecules into polymer matrix results in a perturbation of the thermodynamic equilibrium and consequently a charge transfer could occur speeding up the deep level charge detrapping.

Dresden electron beam ion trap: Status report and next developments

The Dresden EBIT is a room-temperature EBIT producing highly charged ions for x-ray spectroscopy as well as for materials modifications and other applications. In the past we have demonstrated the production of ions such as Ar18+, Fe26+, Kr35+, Xe46+, and Ir67+. Here we give a report on the further development of this ion source to increase the electric trap capacity involving the production of a greater amount of highly charged ions.

Design and prototyping of Stark atom chip for electric trapping of laser-cooled atoms

An electric trapping of laser-cooled neutral strontium (Sr) atoms on a chip with micro-electrodes has been successful. The device is called “Stark atom chip” since it makes use of Stark effects on neutral atoms in electric fields. In this paper, our design and prototyping of the Stark atom chip with high aspect ratio electrodes precisely built on a surface are described. The functional requirements of the chip are specified during the discussion of designing the device. The authors design a novel process for fabrication of high aspect ratio electrodes. A focused ion beam (FIB) is used for precision fabrication of the prototype.

Electrical charge trapping at defects on the Si(111)7×7 surface

We report on a direct measurement of electron trapping at defects on the Si(111)7×7 surface, by combining Kelvin probe force microscopy (KPFM) and scanning tunneling microscopy (STM) measurements. One-dimensional defects of atomic steps and two-dimensional defects of disordered domains were found on the surface. STM reveals that the disordered domain is located in the intersection area between three 7×7 domains. KPFM measurement shows that electrons are trapped at both the atomic steps and the disordered domains, and this electron trapping gives rise to a larger local work function on the defect region than on the defect-free 7×7 regions.

Small‐signal characteristics of organic semiconductors with continuous energy distribution of traps

AbstractThe electrical characteristics of organic light emitting devices containing a continuous distribution of trap states in the forbidden gap are obtained by numerically solving the basic semiconductor equations for the steady state and under small‐signal conditions. The spatially‐dependent occupied trap states, which are described by an explicit density of states function, modify the charge distribution within the structure and the shape of the electric field and the carrier current densities. The effect of the modulation frequency, the applied voltage and the device temperature are studied for a hole conducting layer with a trap density of states consisting of a double gaussian profile and for a given set of microscopic parameters including the carrier mobilities and thermal velocities, the capture cross sections, and the residual shallow impurity concentration. The frequency‐dependent loss and capacitance curves are obtained for various experimental conditions, like temperature and applied steady‐state voltage. Effects of parameters describing electrical contacts and trap density of states are shown. Such results are particularly useful for the analysis of experimental electrical characteristics obtained by thermal admittance spectroscopy. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Image processing for HTS SQUID probe microscope

An HTS SQUID probe microscope has been developed using a high-permeability needle to enable high spatial resolution measurement of samples in air even at room temperature. Image processing techniques have also been developed to improve the magnetic field images obtained from the microscope. Artifacts in the data occur due to electromagnetic interference from electric power lines, line drift and flux trapping. The electromagnetic interference could successfully be removed by eliminating the noise peaks from the power spectrum of fast Fourier transforms of line scans of the image. The drift between lines was removed by interpolating the mean field value of each scan line. Artifacts in line scans occurring due to flux trapping or unexpected noise were removed by the detection of a sharp drift and interpolation using the line data of neighboring lines. Highly detailed magnetic field images were obtained from the HTS SQUID probe microscope by the application of these image processing techniques.

Dresden EBIT: The next generation

To enhance the performance of the Dresden EBIT the prototype of a new room-temperature source of highly charged ions, the Dresden EBIS, has been developed and put into operation. The aim of the development is the increase of the electric trap capacity corresponding to a higher quantity of highly charged ions in the trap. Hence, to meet the necessary requirements the trap length has been extended from 2cm to 6cm. The SmCo5 permanent magnets are substituted by NdFeB magnets and the setup has been redesigned for electron current emission of up to 400mA. This configuration allows to produce highly charged ions up to bare nuclei for elements of the 3d-region and up to neon-like ions for high-Z elements. The ion production in the source is sufficient for spectroscopy of individual X-ray transitions. Ion pulses with an amplitude of several nanoampere can be extracted from the source. Results from X-ray spectroscopic investigations of transitions in Kr34+ and Xe44+ are presented. Furthermore ion extraction experiments with argon and iron ions of the helium-like and adjacent ion charge states will be discussed.

Ac Electric Trap for Ground-State Molecules

We here report on the realization of an electrodynamic trap, capable of trapping neutral atoms and molecules in both low-field and high-field seeking states. Confinement in three dimensions is achieved by switching between two electric field configurations that have a saddle point at the center of the trap, i.e., by alternating a focusing and a defocusing force in each direction. The ac trapping of 15ND(3) molecules is experimentally demonstrated, and the stability of the trap is studied as a function of the switching frequency. A 1 mK sample of 15ND(3) molecules in the high-field seeking component of the |J,K=|1,1 level, the ground state of para-ammonia, is trapped in a volume of about 1 mm(3).

The effect of Zn concentration on some physical properties of tin oxide films obtained by ultrasonic spray pyrolysis

SnO 2 and SnO 2/Zn, at the Zn percentages of 10 and 30, films were prepared at the substrate temperature of 350±5 °C by ultrasonic spray pyrolysis (USP) technique, and the effect of Zn incorporation on the some physical properties of SnO 2 films was investigated. To possess information about the electrical properties of all films, their electrical resistivities, conduction mechanisms, activation and trap energies were investigated. The film structures were studied by X-ray diffraction. Surface morphologies and elemental analyses of the films were studied scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. It can be inferred from all investigations that some physical properties of SnO 2 films remarkable changed with Zn concentration.

Espécies de Trichogramma (Hymenoptera: Trichogrammatidae) coletadas em armadilha de sucção em reserva florestal

For the first time an electrical suction trap was used to collect specimens of Trichogramma. The total of 551 Trichogramma specimens were collected belonging to nine species namely T. acuminatum Querino & Zucchi, T. alloeovirilia Querino & Zucchi, T. bruni Nagaraja, T. parrai Querino & Zucchi, T. pretiosum Riley, T. pusillus Querino & Zucchi, T. tupiense Querino & Zucchi, T. zucchii Querino and Trichogramma sp. aff. pintoi. T. bruni was the most abundant and frequent species. The relative frequency was less than 2% for the remaining species. The electrical suction trap was shown useful to collected Trichogramma specimens in areas where host insect eggs are difficult to find.

Conduction and trapping mechanisms in SiO2 films grown near room temperature by multipolar electron cyclotron resonance plasma enhanced chemical vapor deposition

Silicon dioxide layers with stoichiometric composition and excellent electrical properties were deposited at a substrate temperature of 60 °C with an electron cyclotron resonance plasma source. This work is focused on determining the electrical conduction and trapping mechanisms of the deposited films. From the temperature dependence of current density–electric field characteristics, Fowler–Nordheim tunneling was found to be the dominant conduction mechanism in SiO2 films obtained with low silane flow and at low pressure. For layers deposited with higher silane flows and higher pressures, the current at low biases is highly dependent on temperature. Positive charge was measured at the Si/SiO2 interface during low electric stress, while electrons were trapped at the interface for electric fields higher than 7 MV/cm. Constant current stress measurements confirmed that low silane flow and low total pressure are suitable deposition conditions for obtaining a film comparable to thermally grown oxide from the reliability point of view.

Electric charge transport and trapping in dielectrics deduced from isothermal and non-isothermal measurements

By sequential use of the isothermal charging, the isothermal discharging, the final thermally stimulated discharge current and the final isothermal discharging current techniques, the charge dynamics in highly insulating materials may be investigated. The method is demonstrated for polyethylene terephthalate. The injected charge for a field of 20 MV m/sup -/1 and polarization temperatures up to 110/spl deg/C is almost totally trapped in the material and is released during the heating of the sample at 180/spl deg/C for a sufficiently long time. A significant current at high temperatures, about 90/spl deg/C above the poling temperature, was observed proving that it originates from charge detrapping. The final thermally stimulated discharge current peaks shift to higher temperature when the polarization temperature increases, and are characterized by activation energies in the range from 1.03 to 1.56 eV. They allowed the identification of the glass transition around 114/spl deg/C. The relaxation time of the trapped charge, at 180/spl deg/C, was determined to be about 3780 s, explaining the very good stability of trapped charge.

Formation of dust layers in the near-electrode area of RF-discharge

The conditions of formation of quasi 2D dust structures in the linear external electric fields are considered. The relationships between the parameters of interparticle interaction potential, number of grains and gradients of field of electric trap are found. The criterion of new dust layer formation is proposed.

Electrical conduction and space charge trapping in highly insulating materials

The electrical conduction in low-density polyethylene (LDPE) was investigated in the temperature range from 20°C to 95°C and for applied fields up to 12 MV m−1. The objective was to study the effects of the space charge (SC) accumulated in the material on the low and medium field quasi-steady-state conductivity in LDPE. Very long time (a week or longer) isothermal current measurements were carried out to focus on the situation when the SC effects are dominant. Complementary results were obtained using the isothermal discharge current, the final thermally stimulated discharge current and the isothermal final discharge current measurements. The results are explained by taking into account the constraint imposed by the trapped SC on charge injection, trapping and transport processes.

Charge‐carrier transport in disordered polymers

AbstractThe general properties of charge‐carrier transport in disordered organic materials are discussed. The spatial correlation between energies of transport sites determined the form of drift‐mobility field dependence. The type of spatial correlation in a disordered material depends on its nature. Mobility field dependences must be different in polar and nonpolar materials. Different methods of mobility calculation from the shape of photocurrent transient were analyzed. A widely used method is very sensitive to the variation of the shape of the transient and sometimes produces results that effectively masquerade the true dependence of the mobility on the electric field or trap concentration. Arguments in favor of the better, more reliable method are suggested. Charge transport in materials containing charged traps was considered without using the isolated trap approximation, and this led to qualitatively different results. The results indicated that the effect of charged traps can hardly be responsible for the experimentally observed transport properties of disordered organic materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2584–2594, 2003

Defect spectroscopy using 1/ fγ noise of gate leakage current in ultrathin oxide MOSFETs

The electrical trap properties in ultrathin oxide MOSFETs are extracted using 1/ f γ low frequency noise components of gate leakage current. The technique is based on the low frequency noise measurements which are capable of probing trap states over the energy and space. The gate voltage is swept between 0.4 and 1.32 V to obtain the different power slopes γ of 1/ f γ noise spectrum. From the measured noise data, the trap parameters such as slow trap densities and capture cross-section are accurately determined as a function of trap energy and trap distance. The 1/ f γ noise measurement results confirm that the capture cross-sections depend strongly on the surface potential, and the slow trap densities estimated near the band edge and at the Si–SiO 2 interface are higher than those near the midgap and deeper distance. Moreover, the parallel conductance spectroscopy of slow traps is reproduced by 1/ f γ low frequency noise measurements, and is verified by the low frequency plateau in measured conductance loss G p( f)/ w. For the purpose of investigating the dependency of trap parameters on the complex admittance of oxide traps, the Cole–Cole plots for different trap profiles, a uniform and exponentially decreasing trap distribution in space, are calculated using the theoretical model. The noise spectroscopy technique further reveal the dynamic evolution of trap states and gives a clear physical understanding of the pertinent low frequency noise sources.

Six new species of Trichogramma Westwood (Hymenoptera: Trichogrammatidae) from a Brazilian forest reserve

An electrical suction trap set in a forest reserve in the State of São Paulo, Brazil, was used to collect Trichogramma species. Six new species were collected, namely Trichogramma acuminatum n. sp., Trichogramma alloeovirilia n. sp., Trichogramma parrai n. sp., Trichogramma pusillum n. sp., Trichogramma tupiense n. sp. and Trichogramma zucchii n. sp., which are being described herein.

Radiation-induced charge trapping in low-k silsesquioxane-based intermetal dielectric films

Radiation-induced charge trapping has been studied in cured hydrogen silsesquioxane low dielectric constant films subjected to electric fields during the radiation process. Evidence is found for electric field-dependent negative charge trapping with a dose/sup 0.47/ variation. The possible origin of the negative charge trapping is discussed.

Electronic traps and percolation paths in electroluminescent polymers

Trap related properties of the electroluminescent polymers poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (MDMO-PPV, OC1C10–PPV) and poly[(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene]-[(4′-(3″,7″-dimethyloctyloxy)phenyl-5)-1,4-phenylenevinylene] are investigated in organic light emitting diode (OLED) devices. By means of the thermally stimulated currents (TSC) technique the densities of occupied states, trap polarities and charge transport mechanisms are studied. The fractional TSC technique in combination with optical trap filling reveals broad density-of-occupied-states distributions for both polymers, ranging from 200 to 600 meV located between the highest occupied molecular orbital and lowest unoccupied molecular orbital levels. Conventional TSC experiments in combination with electrical trap filling allow to distinguish between electron and hole traps. In OC1C10–PPV both trap polarities are detected whereas in the copolymer only hole traps and no electron traps were found. In addition, a TSC study on optical and electrical trap filling in OLED devices strongly suggests the presence of percolation paths. Despite larger charging currents in the electrical trap filling case no or much smaller TSC signals were detected in comparison with the optical trap filling case.

Managing the horn fly (Diptera: Muscidae) using an electric walk-through fly trap.

An electric walk-through fly trap was evaluated for the management of the horn fly, Hematobia irritans (L.), on dairy cattle in North Carolina over 2 yr. The trap relies on black lights and electrocution grids to attract and kill flies that are brushed from the cattle passing through. During the first season, horn fly densities were reduced from >1,400 to <200 flies per animal. Horn fly density averaged 269.2 +/- 25.8 on cattle using the walk-through fly trap twice daily, and 400.2 +/- 43.5 on the control group during the first year. The second year, seasonal mean horn fly density was 177.3 +/- 10.8 on cattle using the walk-through fly trap compared with 321.1 +/- 15.8 on the control group. No insecticides were used to control horn flies during this 2-yr study.