Trapping Characteristics Research Articles

An Electron and Hole Trap Energy Distribution Estimation Model and Its Application in Polypropylene Nanocomposites

To differentiate the electron and hole traps inside polymers, a model based on the pulsed electro-acoustic (PEA) method is proposed. It is premised that under short-term DC electric field polarization at relatively low temperature, the homocharge is injected into the sample to a shallow depth and dominates the space charge distribution. Thus, the homocharge near the ground electrode and the high voltage electrode can be separated. During depolarization, only the homocharge near the ground electrode is analyzed to reduce the influence of ultrasonic wave attenuation, which also results in unipolar space charge decay behavior being obtained. The isothermal relaxation current (IRC) theory is then employed to obtain the unipolar quasi-continuous trap energy distribution based on the space charge decay. Thereby, the electron and hole traps can be differentiated by applying positive and negative DC electric field polarization, respectively. The experimental results of low density polyethylene (LDPE) verify the validity of the proposed model. Based on the model, polypropylene (PP) and PP/MgO nanocomposites are studied to explore the effect of MgO doping on the trap characteristics. The results show that numerous electron deep traps are introduced into the nanocomposites due to the intrinsic properties of nanoparticles. Besides, the heterogeneous nucleation of the nanoparticles increases the crystal/amorphous and crystal/vacuum interfaces, which may be the main reason for the increase of hole trap density of nanocomposites.

Variable temperature persistent luminescence properties of phosphors with continuous traps

A yellow long persistent luminescence (LPL) phosphor of Sr3Ga4O9:Bi3+ were synthesized by a simple solid-state method. The luminescence properties have been investigated by photoluminescence (PL) spectra, LPL spectra, afterglow decay curves and thermoluminescence (TL) curves. A series of the excitation time and decay time dependent TL experiments have been conducted, and the trap characteristics of the phosphor were studied. The LPL can be detected more than 10 h, which is due to the fact that the feasible trap depth ensures the slow release of charge carriers. The results of LPL properties at variable temperature show that the phosphor has a broad application prospect in high-temperature environments.

Investigation on the interface trap characteristics in a p-channel GaN MOSFET through temperature-dependent subthreshold slope analysis

In this paper, a simple method based on subthreshold slopes was proposed to investigate the interface trap characteristics in a p-channel GaN MOSFET with a p-GaN/AlGaN/GaN structure on Si. The energy distribution of the interface trap density has been extracted from the analysis of the transfer characteristics in the subthreshold region of operation. The interface trap densities and respective energy distribution at both room temperature and 150 °C were also calculated from the ac conductance measurements at corresponding applied biases. Both characterization methods show similar results of trap densities and energy levels.

Study of traps in low-temperature polysilicon thin film transistors using a current transient method

The trap characteristics of low-temperature polysilicon thin film transistors (TFTs) are studied using a current transient method that is based on the trapping and detrapping of charge carriers from the trap sites in the device. Analysis of the measured current transient curve allowed three types of detrapping behavior to be identified, each of which displayed a different time constant, activation energy, and spatial position. This current transient method can be integrated into the negative bias temperature instability stress test used for the reliability study. The peak amplitudes of the traps increase because of the stress applied in the test, thus demonstrating that the degradation mechanism of the TFTs is closely related to changes in the traps in these devices.

The impact of heterogeneity on the capillary trapping of [formula omitted] in the Captain Sandstone.

A significant uncertainty which remains for CO2 sequestration, is the effect of natural geological heterogeneities and hysteresis on capillary trapping over different length scales. This paper uses laboratory data measured in cores from the Goldeneye formation of the Captain D Sandstone, North Sea in 1D numerical simulations to evaluate the potential capillary trapping from natural rock heterogeneities across a range of scales, from cm to 65m. The impact of different geological realisations, as well as uncertainty in petrophysical properties, on the amount of capillary heterogeneity trapping is estimated. In addition, the validity of upscaling trapping characteristics in terms of the Land trapping parameter is assessed. The numerical models show that the capillary heterogeneity trapped CO2 saturation may vary between 0 and 14% of the total trapped saturation, depending upon the geological realisation and petrophysical uncertainty. When upscaling the Land model from core-scale experimental data, using the maximum experimental Land trapping parameter could increase the expected heterogeneity trapping by a factor of 3. Conversely, depending on the form of the imbibition capillary pressure curve used in the numerical model, including capillary pressure hysteresis may reduce the heterogeneity trapping by up to 70%.

Optical Trapping-Induced New Polymorphism of β-Cyclodextrin in Unsaturated Solution

A new polymorph of β-cyclodextrin (β-CD) was produced by optical trapping with a 1064 nm continuous wave laser beam in D2O solution. Upon optical trapping of β-CD in unsaturated solutions, a single prism crystal or multiple plate crystals were formed at and near the laser focus. The resulting crystals differed in morphology and in the Raman spectrum. Furthermore, the solubility of the plate crystal in D2O was much lower than that of the prism crystal, implying that the former crystal is thermodynamically more stable than the latter. The single-crystal X-ray crystallographic analysis showed that the prism crystal has practically the same crystallographic parameters as the crystal reported for β-CD dodecahydrate and is thought to be the thermodynamically most stable phase. These results reveal that the plate crystal is a new polymorph characteristic of optical trapping. Crucially, this is the first success to produce a new polymorph via the laser-induced crystallization method. More interestingly, the generation probability of these two polymorphs turned out to be a critical function of the initial β-CD concentration, laser power, and laser polarization mode. In particular, the polymorphism could be entirely controlled by adjusting the initial concentration, which allowed us to obtain pure prism and plate crystals at high and low CD concentrations, respectively. The dynamics and mechanism of this unique optical trapping-induced polymorphism are discussed in terms of the pre-nucleation cluster size determined by the initial concentration, the trapping efficiency as a function of the cluster size and the laser power, and the molecular alignment in the pre-nucleation clusters steered by the laser polarization mode.

Enhanced direct‐current breakdown strength of Al2O3/epoxy resin composites through plasma fluoridation of fillers interface

AbstractHerein, a method for improving the direct‐current (DC) breakdown strength of the epoxy resin (ER) was proposed. Nano‐Al2O3 was treated with CF4/Ar plasma and doped into the epoxy resin matrix to obtain epoxy composites with high DC breakdown strength in both extremely uneven and slightly uneven electric fields. The reaction essence of plasma fluoridation was characterized, and the dielectric spectrum, volume conductivity, space charge, and carrier trap characteristics of the modified composites were studied. The plasma fluoridation at the fillers‐matrices interface is an effective pretreatment method to enhance insulation, exhibiting good applicability to ceramic/polymer composites.

Electrical Aging Effect on Breakdown and Charge Trap Characteristics of Polyimide Films With Different Thickness in LN2

The Polyimide (PI) film, as an excellent insulating material, is broadly utilized in superconductivity power equipment, especially under low temperature. There is an enormous influence on the breakdown performance of polymers because of the presence of surface and space charge. In order to investigate the electrical aging impact on breakdown and trap characteristics of PI films with 0.1 mm and 0.125 mm thickness, the samples suffer from diverse degrees of electrical aging in liquid nitrogen (LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The insulation strength test has been carried out on the PI film samples under different electrical aging stages in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . The isothermal surface potential decay (ISPD) method is performed on the PI films to explore the behaviors of trapped charges, and the trap characteristics of the PI films are obtained. Those results indicate that the breakdown strength of the thinner PI film (0.1 mm) in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is higher than that of the thicker one (0.125 mm), and the breakdown field strength reduces with the electrical aging time increasing. The ISPD measurement results indicate that the average decay rate of surface potential in the 0.125 mm PI is faster than the other thickness during the whole decay process.

Circular nanocavity substrate-assisted plasmonic tip for its enhancement in nanofocusing and optical trapping.

Plasmonic tip nanofocusing has widely been applied in tip-enhanced Raman spectroscopy, optical trapping, nonlinear optics, and super-resolution imaging due to its capability of high local field enhancement. In this work, a substrate with a circular nanocavity is proposed to enhance the nanofocusing and optical trapping characteristics of the plasmonic tip. Under axial illumination of a tightly focused radial polarized beam, the circular nanohole etched on a metallic substrate can form a nanocavity to induce an interference effect and further enhance the electric field intensity. When a plasmonic tip is placed closely above such a substrate, the electric field intensity of the gap-plasmon mode can further be improved, which is 10 folds stronger than that of the conventional gap-plasmon mode. Further analysis reveals that the enhanced gap-plasmon mode can significantly strengthen the optical force exerted on a nanoparticle and stably trap a 4-nm-diameter dielectric nanoparticle. Our proposed method can improve the performance of tip-enhanced spectroscopy, plasmonic tweezers and extend their applications. We anticipate that our methods allow simultaneously manipulating and characterizing single nanoparticles in-situ.

DC Breakdown of XLPE Modulated by Space Charge and Temperature Dependent Carrier Mobility

In this paper, the dependence of XLPE electrical breakdown on carrier mobility controlled by both electric field and temperature is evaluated by simulations and experiments. The molecular chain displacement model incorporating the thermoelectric effect of carrier mobility is examined to elucidate the experimental results. Trapping and de-trapping characteristics of space charge and mobility dynamics are modeled using hopping and Poole-Frenkel mechanisms. The experimental outcomes reveal that the DC electrical breakdown reduces with corresponding increment in temperature and thickness. Trapping parameters are estimated from experiments for simulations. The DC breakdown strength from experiments represents an inverse power relation with both the insulation thickness and temperature. The simulation results of molecular chain model with hopping mobility express more permanence with experimental results in comparison with Poole-Frenkel mobility.

Frequency-Domain Spectroscopy and Charge Trap Characteristics of Cellulose Based Pressboard Modified by Nano-TiO2 Particles

Dielectric response and charge decay test are widely used for evaluating the electric properties of the insulation pressboards in the converter transformer. In this paper, Frequency Domain Spectroscopy (FDS) test, breakdown test, and charge decay characteristics experiments are carried out on the cellulose pressboards modified by TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> with different mass fractions and diameters. The FDS of the modified cellulose pressboards at ambient temperature is measured from 0.0001 to 1000 Hz by IDAX 300. The process is conducted at the laboratory to study the characteristics parameters of the dielectric response behaviors, such as complex relative permittivity. The results show that the values of the relative permittivity for the insulation pressboards modified by TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (5 wt%, 10 nm) are reduced. To verify the accurate results, the microstructures of the pressboards modified by 5 wt% with 10 nm diameter are observed by a Scanning Electron Microscope (SEM). The breakdown strength tests are carried on the samples modified by 1 wt%, 3 wt%, 5 wt%, 7 wt% with 10 nm TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> under the intensity electric and high-temperature field, respectively. The values of the breakdown strength are increased by 38% and 11.5% for single layer samples and oil/pressboard composite insulation models modified by 5 wt% nano-TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> filler. In addition, the charge decay characteristics are tested on the samples. The proper proportion additions can reduce the trap density.

Light absorption enhancement by incorporating nanostructured-diatomite for improving performance of polymeric photodetector

In this work, the nano-structured diatomite (DIA) was first incorporated into poly (3-hexylthiophene) (P3HT) thin film, and developed as a light-trapping layer in polymeric photodetector. DIAs are ubiquitous in nature and adaptive evolution has given them the ability to adsorb or light trapping. As a natural, inexpensive silica material, diatomite can act as a light scatterer in the active layer. Compared with the P3HT device, the average photocurrent increased up to 100 % after the incorporation of DIA, which benefits from its light trapping characteristics. As a result, the DIA photodetector has a significantly improved photo-response ability, with a higher responsivity (R) (average increase up to 112 %) and detectivity (D*) (average increase up to 139 %). Moreover, linear dynamic range (LDR) of the device also improved, the response under different light conditions is increased by 15.3 %.

Manipulating and measuring single atoms in the Maltese cross geometry

Background: Optical microtraps at the focus of high numerical aperture (high-NA) imaging systems enable efficient collection, trapping, detection and manipulation of individual neutral atoms for quantum technology and studies of optical physics associated with super- and sub-radiant states. The recently developed “Maltese cross” geometry (MCG) atom trap uses four in-vacuum lenses to achieve four-directional high-NA optical coupling to single trapped atoms and small atomic arrays. This article presents the first extensive characterisation of atomic behaviour in a MCG atom trap. Methods: We employ a MCG system optimised for high coupling efficiency and characterise the resulting properties of the trap and trapped atoms. Using current best practices, we measure occupancy, loading rate, lifetime, temperature, fluorescence anti-bunching and trap frequencies. We also use the four-directional access to implement a new method to map the spatial distribution of collection efficiency from high-NA optics: we use the two on-trap-axis lenses to produce a 1D optical lattice, the sites of which are stochastically filled and emptied by the trap loading process. The two off-trap-axis lenses are used for imaging and single-mode collection. Correlations of single-mode and imaging fluorescence signals are then used to map the single-mode collection efficiency. Results: We observe trap characteristics comparable to what has been reported for single-atom traps with one- or two-lens optical systems. The collection efficiency distribution in the axial and transverse directions is directly observed to be in agreement with expected collection efficiency distribution from Gaussian beam optics. Conclusions: The multi-directional high-NA access provided by the Maltese cross geometry enables complex manipulations and measurements not possible in geometries with fewer directions of access, and can be achieved while preserving other trap characteristics such as lifetime, temperature, and trap size.

The Trapped Charges at Grain Boundaries in Perovskite Solar Cells

AbstractThe performance of perovskite solar cells is greatly affected by the crystallization of the perovskite active layer. Perovskite crystal grains should neatly arrange and penetrate the entire active layer for an ideal perovskite crystallization. These kinds of crystallized perovskite films exhibit fewer defects and longer carrier lifetime, which is beneficial to enhance the performance of perovskite solar cells. Here, by testing the residual charge of perovskite solar cells with different crystallization conditions, it is demonstrated that the residual charge exists widely at the grain boundary, which is parallel to the device, and the residual charge is related to the performance of the perovskite solar cells. Single crystal grains neatly arranged and penetrate the entire active layer can generate less residual charge and improve device performance of the perovskite solar cells. The results also show that the long decay time of open‐circuit voltage comes from the detrapping of trapped carriers. The residual charge testing technology provides a new idea for the investigation of carrier trap and detrap characteristics in photovoltaic devices.

Time‐resolved particle image velocimetry analysis and computational modeling of transient optically induced electrothermal micro vortex

Trapping, sorting, transportation, and manipulation of synthetic microparticles and biological cells enable investigations in their behavior and properties. Microfluidic techniques like rapid electrokinetic patterning (REP) provide a non-invasive means to probe into the nature of these micro and nanoparticles. The opto-electrically induced nature of a REP micro vortex allows tuning of the trap characteristics in real-time. In this work, we studied the effects of transient optical heating on the induced electrothermal vortex using micro-particle image velocimetry (μ-PIV) and computational modeling. A near infra-red (980nm) laser beam was focused on a colloidal suspension of 1μm polystyrene beads sandwiched between two parallel-plate electrodes. The electrodes were subjected to an AC current. The laser spot was scanned back-and-forth in a line, at different frequencies, to create the transient vortex. This phenomenon was also studied with a computational model made using COMSOL Multiphysics. We visualize fluid flow in custom-shaped REP traps by superposing multiple axisymmetric (spot) vortices and discuss the limitations of using superposition in dynamically changing traps.

Effect of Bismuth Ferrite Nanometer Filler Element Doping on the Surface Insulation Properties of Epoxy Resin Composites.

In the direct current electric field, the surface of epoxy resin (EP) insulating material is prone to charge accumulation, which leads to electric field distortion and damages the overall insulation of the equipment. Nano-doping is an effective method to improve the surface insulation strength and DC flashover voltage of epoxy resin composites. In this study, pure bismuth ferrite nanoparticles (BFO), as well as BFO nanofillers, which were doped by La element, Cr element as well as co-doped by La + Cr element, were prepared by the sol-gel method. Epoxy composites with various filler concentrations were prepared by blending nano-fillers with epoxy resin. The morphology and crystal structure of the filler were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The effects of different filler types and filler mass fraction on the surface flashover voltage, charge dissipation rate, and trap characteristics of epoxy resin composites were studied. The results showed that element doping with bismuth ferrite nanofillers could further increase the flash voltage of the composites. The flashover voltage of La + Cr elements co-doped composites with the filler mass fraction of 4 wt% was 45.2% higher than that of pure epoxy resin. Through data comparison, it is found that the surface charge dissipation rate is not the only determinant of the flashover voltage. Appropriately reducing the surface charge dissipation rate of epoxy resin composites can increase the flashover voltage. Finally, combining with the distribution characteristics of the traps on the surface of the materials to explain the mechanism, it is found that the doping of La element and Cr element can increase the energy level depth and density of the deep traps of the composite materials, which can effectively improve the flashover voltage along the surface of the epoxy resin.

Cobalt‐Nanoporous Carbon Functionalized Nanocomposite‐Based Triboelectric Nanogenerator for Contactless and Sustainable Self‐Powered Sensor Systems

AbstractTriboelectric nanogenerators (TENGs), which operate in contactless mode and avoid physical contact, are highly attractive for self‐powered sensor systems aiming to achieve long‐term reliable operation and reduce rubbing friction. Herein, an ultra‐flexible and high‐performance contactless double‐layer TENG (CDL‐TENG) is first designed and fabricated using a metal–organic framework‐based cobalt nanoporous carbon (Co‐NPC)/Ecoflex with MXene/Ecoflex nanocomposite layer for self‐powered sensor applications. The porous structure of the Co‐NPC provides a high‐surface‐area of the nanocomposite and the charge storage layer of the MXene/Ecoflex nanocomposite accumulates more negative charge to improve the functionality of the CDL‐TENG two and three times, respectively. Compared with Ecoflex film‐based TENGs, the fabricated CDL‐TENG exhibits an eight‐fold slower decay rate owing to charge trapping characteristics, which were confirmed by surface potential measurements. The CDL‐TENG shows excellent humidity and acceleration sensitivity of about 0.3 V/% and 2.06 Vs2 m−1. The CDL‐TENG also offers non‐contact position detection performance in the 20 cm range. Furthermore, the CDL‐TENG is successfully integrated with mobile‐vehicles and an intelligent robot to perform obstacle and human‐motion detection. Finally, a contactless door‐lock password authentication system was demonstrated. These multifunctional benefits make it useful for numerous applications, including artificial intelligence, human‐machine interfaces, and self‐powered sensors.

Experimental Study on Damage Mechanism of Partial Discharge of Oil-Immersed Laminated PMIA Paper

PMIA (Poly-m-phenylene isophthalamide) is an ideal substitute for traditional cellulose paper in oil-immersed paper insulating scenarios. This paper studies the partial discharge characteristics of oil-immersed laminated PMIA. According to the q-φ scatter diagram, discharge quantity and discharge phenomenon, the partial discharge process of PMIA is divided into 3 stages: creeping discharge, co-existence discharge and pre-breakdown. The micro-structure and chemical components of damaged PMIA are presented. The carbon trace, functional groups, carrier trap characteristics and residual insulation strength in different stages of partial discharge are studied. This paper provides a theoretical basis for the application of PMIA in electrical insulation.

Numerical Simulation on Charge Transport and DC Breakdown in Polyethylene-Based Micro-h-BN/Nano-SiO2 with Filler Orientation Dependent Trap Energy

In order to improve the thermal conductivity and the insulation properties of polyethylene (PE) used as cable insulation under DC stress, hexagonal boron nitride (h-BN) and inorganic particles have been considered as micro-filler and nano-filler, respectively. As a 2D material, the orientation of h-BN possibly affects the insulation properties of the polymer. It is important to understand the influence of the filler orientation on the insulation performance of the polymer. In this work, a numerical simulation has been performed to investigate the effect of orientation of micro-h-BN on charge transport and DC breakdown of PE-based micro/nano-composites and a comparison between the simulation result and previous literature data has been conducted. The h-BN was designated to be parallel, perpendicular to the normal sample surface vector (the direction of electric field in this work) or randomly distributed in the matrix, and the charge transport behavior and DC breakdown strength in the samples were discussed by using the bipolar charge transport (BCT) model. The results indicated that when the h-BN was perpendicular to the normal vector, the density of trapped charge was the largest and the DC breakdown strength was the highest among the three cases studied. It is suggested that the charge trapping/de-trapping processes and the electric field in the sample vary with the orientation of h-BN through tailoring the trap characteristics of the material.

Iterative dual boundary element analysis of a wavy porous plate near an inclined seawall

In this work, wave trapping characteristics of a permeable composite wavy barrier located near an inclined seawall are examined under the framework of linear potential flow theory. For the waves past the thin barrier, a semi-empirical discharge equation having a quadratic pressure drop along with the velocity continuum is considered. The boundary value problem is solved using the dual boundary element method (DBEM). The accuracy of the numerical results is ascertained with a numerical model based on an independently developed multi-domain boundary element method (MBEM). Various numerical results such as wave reflection, wave run-up, the vertical force on the barrier and horizontal force on the wall are discussed considering various values of barrier porosity, number of ripples, ripple amplitude, relative spacing between the wall and barrier, relative submergence depth, seawall inclination, and seawall porosity. The numerical results suggest that the performance of the wavy barrier within sight of partial reflection leeward inclined wall is marginal for the design of the development of breakwaters as contrasted to the vertical and seaward inclined wall. The ripple amplitude minimizes the vertical force on the wavy barrier and the reduction is 63% for the non-dimensional ripple amplitude a/B=0.25 as compared to a flat plate where ‘a’ and ‘B’ refers to ripple amplitude and plate width respectively. The parametric study is expected to serve as an incentive for the design and development of composite wavy porous plates to secure the available seawalls.