Trapping Properties Research Articles

Three newly developed BeO-based OSL dosimeters

This work presents the structural, morphological, luminescent and dosimetric characteristics of newly produced BeO based ceramic pellets, namely, BeO:Na5%,Ce0.01%,Er0.01%, BeO:Na5%,Ce0.005%,Tb0.05%, and BeO:Na5%,Ce0.01%,Dy0.01% by a simultaneous comparison with the commercially developed BeO Thermalox 995 chips. In this study, the BeO-based ceramics have been prepared using the co-precipitation synthesis method. Their phase formation and morphology have been confirmed by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Energy Dispersive x-ray (EDS) analyses. To investigate the luminescence characteristics of the studied samples for dosimetry applications, the trap properties were identified using the TL and OSL emissions, step-annealing curve analyses, and experimental determination of temperature dependence. It was investigated that luminescence bands located between 300 and 400 nm (i.e., 3–4 eV) are dependent on the same luminescence mechanism in all radiation-induced luminescence effects used in dosimetry (RL, TL, and OSL). These newly developed BeO dosimeters with high OSL sensitivity and good reproducibility gave a linear response to β-radiation exposure from 0.5 to 100 Gy. The energy response of the samples was discussed. Negligible decay of stored OSL was determined as almost 7% after 3 months of storage. The application of BeO dosimeters for medical monitoring was discussed in comparison to the OSL evaluations from the Thermalox 995.

Light behaviors outside a black hole surrounded by dark matter

Here we show the light behaviors outside a Schwarzschild black hole that is surrounded by a dark matter model proposed by Konoplya (see Konoplya R., Phys. Lett. B, 795 (2019) 1). It is worth mentioning that dark matter is studied for the first time in an optical system by transformation optics theory. Different from other works of mimicking curved spaces with geodesic equations, we calculate ray trajectories using the equivalent anisotropic material tensor, which can also be used to simulate field patterns for wave optics. The results from geometric optics and wave optics agree with each other perfectly, showing the gravitational lensing effects and light trapping properties, revealing the influences of dark matter on the black hole shadow and gravity, which can give some hints for future observations.

Dynamical power flow and trapping-force properties of two-dimensional Airy-beam superpositions

Abruptly autofocusing beams have attracted more and more attention because of their potential applications in optical manipulation. Here, we not only experimentally and theoretically investigate dynamical propagation properties of two-dimensional (2D) Airy--beam superpositions in free space and disordered media, but also study their stability, dynamical power flow, and trapping force properties from a different point. 2D Airy-beam superpositions have superior stability and can easily control their autofocusing propagations and trapping forces through a changing number of superimposing beams, truncated factor, scale factor, initial position, and the angle between two wings of 2D Airy beams. Based on the analysis of the evolution of power flow and trapping force, it is demonstrated that 2D Airy-beam superpositions repeat many autofocusing propagations, leading to a series of focuses and stable trapping positions to appear in propagation. Compared to traditional autofocusing beams, i.e., circular Airy beams and one-dimensional Airy-beam superpositions, 2D Airy-beam superpositions can show a better optical trapping performance in theory. Moreover, we used 2D Airy-beam superpositions as an optical tweezer to trap particles in the experiment and quantitatively analyzed trapping force properties such as trap stiffness via the power spectra method. The experimental results further demonstrate that 2D Airy-beam superposition can show better optical trapping ability than the circular Airy beam. Our work provides a systematic understanding of the propagation and trapping properties of 2D Airy-beam superpositions in theory and experiment. It is helpful for the further applications of autofocusing beams on the optical tweezer, especially in biomedical research.

Analysis of the Effects of High-Energy Electron Irradiation of GaN High-Electron-Mobility Transistors Using the Voltage-Transient Method

The effects of high-energy (1 MeV) electron irradiation on the electrical and trapping properties of AlGaN/GaN high-electron-mobility transistors (HEMTs) are investigated systematically. When the irradiation fluence increases from 5 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 1 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the drain-source current also increases and the threshold voltage shifts toward the negative direction. A Raman spectroscopy study shows that electron irradiation induces strain relaxation in the HEMT, which results in an improvement in the device's electrical characteristics. In particular, three traps in the device are identified using the voltage-transient method and the trapping effects in the HEMT are investigated after the final irradiation. When compared with the transient voltages during the pristine stage, the absolute amplitudes of the three traps in the device decrease after irradiation, which indicates a reduction in the density of the traps. Furthermore, it is proposed that the time constants of the three traps increase while the energy levels remain unchanged, which is ascribed to the strain relaxation and the structural ordering of the defects after electron irradiation. The observed changes in the trapping behaviors are consistent with the improvement in the electrical properties of the device and the shift in the Raman spectra.

Effects of gamma irradiation on GaN high-electron-mobility transistors characterized by the voltage-transient method

The effects of gamma irradiation on the electrical and trapping properties of AlGaN/GaN high-electron-mobility transistors (HEMTs) are investigated in detail. During the irradiation, the gate–source leakage current of the HEMT is monitored online when applying a reverse gate voltage. The variations of electrical properties of the device, including an increase in drain–source current, the negative threshold voltage shift, and a decrease of leakage current, are observed. In particular, three traps in the device are identified using the voltage-transient method and the variations of these traps after irradiation are also investigated. The results show that the absolute amplitudes of the three traps in the device decrease after irradiation, which indicates a reduction in the density of the traps. Furthermore, it is proposed that the time constants and energy levels of the three traps decrease after irradiation. The observed changes in the trapping behaviors are ascribed to the structural ordering of the defects, which is consistent with the improvement in the electrical characteristics of the device.

A high-precision current measurement platform applied for statistical measurement of discharge current transient spectroscopy of traps in SiN dielectrics

This paper presents a current measurement platform to measure current across dielectrics with a high-precision of 10−17 A from a large number of small capacitors at high speed. The developed platform consists of a common readout circuit part and a dielectric part formed on the circuit part by a simple process. A platform chip with 10 μm pitch 384H × 360V cells was fabricated using a 0.18 μm CMOS technology and silicon nitride (SiN) films were formed by plasma-enhanced CVD (PECVD) as a measurement target. The trap property of SiN films in metal–insulator–metal (MIM) capacitors was statistically measured by discharge current transient spectroscopy (DCTS) using the developed platform. The measured average energy levels of traps (E c –E t ) were 0.21–0.25 eV, which is in good agreement with that of the discrete samples. The distributions of energy levels and densities of traps measured with different film thicknesses and areas are also presented and discussed.

Morphology evolution of the light trapping structure using atmospheric plasma textured c-Si wafer for silicon solar cells

Applying atmospheric plasma etching to the surface texturing process of silicon solar cells is a promising strategy for the current photovoltaic manufacturing industry due to its low equipment cost and good fabrication flexibility. This paper investigates the morphology evolution of the silicon surface etched by an Ar/CF4/O2 plasma and the associated optical properties. Results show that the generation of the light trapping structure on the polished silicon surface can be divided into two stages on the basis of the multi-scale morphological images and the quantitative evaluation of roughness parameters. The initial roughening stage mainly involves the formation of high-frequency nanoroughness that can act as an effective medium layer with a gradual refractive index. The resulting optical medium effect can reduce the surface reflectance within a broad range of wavelengths. At the next texturing stage, the low-frequency and high-amplitude microroughness dominates the morphology of the etched silicon surface. It features inverted parabolic structures with a high aspect ratio, which can cause multiple reflections of the incident light. The optical medium effect resulting from the nanoroughness is also inherited. Thus, the anti-reflectance property of the etched silicon surface is greatly improved. This work demonstrates that the light trapping properties of silicon surface etched by atmospheric plasma jet are a synergy of the optical medium effect and geometrical optics. Insights into the morphology evolution and optical properties of the textured surfaces are important for developing a new surface texturing process of silicon solar cells.

Surface engineering enables highly reversible lithium-ion storage and durable structure for advanced silicon anode

Silicon has been regarded as one of the most promising anodes for lithium-ion batteries (LIBs). However, state-of-the-art silicon-based material suffers from huge volume changes and poor conductivity. Here, we develop a surface engineering strategy to address the intrinsic defects. A dual-binder formed by cross-linking sodium alginate and chitosan is investigated and proposed. Moreover, a 3,4,9,10-perylenetetracarboxylic diimide (PDI) shell is introduced into the Si@SiO x surface. Density functional theory (DFT) calculations reveal that π-π stacking PDI with Li-ion trapping properties is compatible with an SA/CS complex (SC) binder through strong adsorption. These factors buffer the interface tension of Si@SiO x and facilitate Li-ion diffusion. The fabricated electrode shows highly reversible lithium-ion storage and long-term stability. Furthermore, a full-cell configuration with lithium nickel cobalt manganate (NCM) as the cathode demonstrates superior electrochemical properties and potential applications. Such surface engineering creates an opportunity for the fabrication of advanced silicon anodes. Surface engineering is guided by theoretical calculations π-π stacking PDI with Li-ion trapping properties are compatible with SC dual-binder Electrochemical mechanisms have been well studied Silicon-based anode materials persistently suffer from low conductivity and drastic volume expansion. In this work, Meng et al. design a surface engineering strategy consisting of a dual-binder and a coating layer with capturing lithium-ion properties. The prepared electrode shows a superior lithium-ion storage capability and long-term stability.

Shielding Effect on Flux Trapping in Pulsed-Field Magnetizing for Mg-B Bulk Magnet

MgB2 superconducting bulk materials are characterized as simple and uniform metallic compounds, and capable of trapping field of non-distorted conical shapes. Although pulsed-field magnetization technique (PFM) is expected to be a cheap and an easy way to activate them, the heat generation due to the magnetic flux motion causes serious degradation of captured fields. The authors precisely estimated the flux trapping property of the bulk samples, found that the flux-shielding effect closely attributed to the sample dimensions. The magnetic field capturing of Ti-5.0wt% sample reached the highest value of 0.76 T. The applied field which reached the centre of the sample surface shifted from 1.0 T to 1.2 T with increasing sample thickness from 3.67 mm to 5.80 mm. This means that the shielding effect was enhanced with increasing the sample thickness. Moreover, Ti-addition affected the frequency of flux jump happenings. The occurrence of flux jumps was suppressed in 5.0wt%Ti-added sample. This means that the heat capacity of the compounds was promoted by Ti addition.

Continuous Breathing Rare-Earth MOFs Based on Hexanuclear Clusters with Gas Trapping Properties

Guest responsive porous materials represent an important and fascinating class of multifunctional solids that have attracted considerable attention in recent years. An understanding of how these structures form is essential toward their rational design, which is a prerequisite for the development of tailor-made materials for advanced applications. We herein report a novel series of stable rare-earth (RE) MOFs that show a rare continuous breathing behavior and an unprecedented gas-trapping property. We used an asymmetric 4-c tetratopic carboxylate-based organic ligand that is capable of affording highly crystalline materials upon controlled reaction with RE cations. These MOFs, denoted as RE-thc-MOF-1 (RE: Y3+, Sm3+, Eu3+, Tb3+, Dy3+, Ho3+, and Er3+), feature hexanuclear RE6 clusters that display a highly unusual connectivity and serve as unique 8-c hemi-cuboctahedral secondary building block, resulting in a new (3,3,8)-c thc topology. Extensive single-crystal to single-crystal structural analyses coupled with detailed gas (N2, Ar, Kr, CO2, CH4, and Xe) and vapor (EtOH, CH3CN, C6H6, and C6H14) sorption studies, supported by accurate theoretical calculations, shed light onto the unique swelling behavior. The results reveal a synergistic action involving steric effects, associated with coordinated solvent molecules and 2-fluorobenzoate (2-FBA) nonbridging ligands, as well as cation-framework electrostatic interactions. We were able to probe the individual role of the coordinated solvent molecules and 2-FBA ligands and found that both cooperatively control the gas-breathing and -trapping properties, while 2-FBA controls the vapor adsorption selectivity. These findings provide unique opportunities toward the design and development of tunable RE-based flexible MOFs with tailor-made properties.

Programmable icosahedral shell system for virus trapping.

Broad spectrum antiviral platforms that can decrease or inhibit viral infection would alleviate many threats to global public health. Nonetheless, effective technologies of this kind are still not available. Here we describe a programmable icosahedral canvas for the self-assembly of icosahedral shells that have viral trapping and antiviral properties. Programmable triangular building blocks constructed from DNA assemble with high yield into various shell objects with user-defined geometries and apertures. We create shells with molecular masses ranging from 43 to 925 Megadaltons (8 to 180 subunits) and with internal cavity diameters ranging up to 280 nm. The shell interior can be functionalized with virus-specific moieties in a modular fashion. We demonstrate this virus-trap concept by engulfing hepatitis B virus (HBV) core particles and adeno-associated viruses (AAV). We show inhibition of HBV core interactions with surfaces in vitro and demonstrate neutralization of infectious AAV exposed to human cells.

EPR characterization in natural quartz samples of a newly discovered hydrogen related defect and already known germanium related defects

The role of hydrogen in the formation and modification of defects in quartz is well known, but still to be clarified is its involvement in trapping and recombination properties of quartz on which its dating characteristics are based. In this work, we studied the thermal stabilities of EPR signals in natural pegmatitic quartz using an X-band spectrometer. We also observed at least two previously unreported EPR signals in quartz, one of them possessing a hydrogen hyperfine structure with large coupling constant. Its thermal stability is intermediate between the well-known [GeO4]- and [GeO4/Li+]0 centres, while the other newly reported signals possess a thermal stability comparable to the latter. The sample has been further studied with a Q-band spectrometer to enhance the resolution of the spectrum. This allowed to confirm, without having to fit or simulate the overlapped signals, the g-factors reported in the literature for Ge related centres, which are strongly overlapped in the X-band. We performed simulations to extrapolate the g-factors and coupling constants of the observed components. We carried out pulse annealing experiments to determine the trap depth of the centres originating such signals. The hydrogen related centre signal has been simulated with the g-tensor's main components being g1 = 2.0007, g2 = 1.9974 and g3 = 1.9929, with coupling constants A1 = 233 MHz, A2 = 235 MHz and A3 = 239 MHz, and trap depth of 1.14 eV.

Characterization and role of deep traps on the radio frequency performances of high resistivity substrates

In this study, high-resistivity gold-implanted silicon substrates developed for radio frequency (RF) applications were characterized. By varying PICTS (Photo-Induced Current Transient Spectroscopy) measurement conditions such as the illumination wavelength, we identified the signature and the nature of four dominant traps. Two were electron traps and the others were hole traps. All of the related defects involved gold atoms. RF simulations of coplanar waveguide transmission lines integrated on these substrates were carried out, based on the trap properties extracted from PICTS results. A good agreement between RF experimental data and simulations was achieved by tuning the trap concentrations. Finally, the gold density extracted from the fit was successfully compared with the secondary ion mass spectrometry profile and an explanation of the role of the traps in RF behavior of the substrate was given.

Statistical moments of the interspike intervals for a neuron model driven by trichotomous noise.

The influence of a colored three-level input noise (trichotomous noise) on the spike generation of a perfect integrate-and-fire (PIF) model of neurons is studied. Using a first-passage-time formulation, exact expressions for the Laplace transform of the output interspike interval (ISI) density and for the statistical moments of the ISIs (such as the coefficient of variation, the skewness, the serial correlation coefficient, and the Fano factor) are derived. To model the anomalous subdiffusion that can arise from, e.g., the trapping properties of dendritic spines, the model is extended by including a random operational time in the form of an inverse strictly increasing Lévy-type subordinator, and exact formulas for ISI statistics are given for this case as well. Particularly, it is shown that at some parameter regimes, the ISI density exhibits a three-modal structure. The results for the extended model show that the ISI serial correlation coefficient and the Fano factor are nonmonotonic with respect to the input current, which indicates that at an intermediate value of the input current the variability of the output spike trains is minimal. Similarities and differences between the behavior of the presented models and the previously investigated PIF models driven by dichotomous noise are also discussed.

Probing the Effect of Surface Modification of MgO Filler on Charge Transport in Polyethylene/MgO Composites: From an Electronic Structure Viewpoint

In this work, with the aid of first-principles calculation, we attempt to clarify whether nanoparticles itself can trap electrons and holes. Polyethylene (PE)/MgO nanocomposite is chosen as a model system. According to the computed adsorption energies, pristine and fully terminated surfaces are stable for the MgO (100) and MgO (111) surfaces, respectively. The electronic structures of several energetically favorable surface configurations are then studied. To probe the behavior of the excess charge, we examined the change in the charge distribution upon electron and hole doping. In the case of ideal MgO, holes are localized within the MgO slab, whereas electrons reside at the PE layer. We also show that the band alignment at the MgO/PE interface and, therefore, the carrier trapping property of MgO, is mainly determined by the intrinsic band edge positions of PE and MgO and the surface dipole of MgO, which can easily be tuned by surface modification.

Pebble Trapping in Vortices: Three-dimensional Simulations

Abstract Disk vortices have been heralded as promising routes for planet formation due to their ability to trap significant amounts of pebbles. While the gas motions and trapping properties of two-dimensional vortices have been studied in enough detail in the literature, pebble trapping in three dimensions has received less attention, due to the higher computational demand. Here we use the Pencil Code to study 3D vortices generated by convective overstability and the trapping of solids within them. The gas is unstratified whereas the pebbles settle to the midplane due to vertical gravity. We find that for pebbles of normalized friction times of St = 0.05 and St = 1 , and dust-to-gas ratio ε = 0.01 , the vortex column in the midplane is strongly perturbed. Yet when the initial dust-to-gas ratio is decreased the vortices remain stable and function as efficient pebble traps. Streaming instability is triggered even for the lowest dust-to-gas ratio ( ε 0 = 10 − 4 ) and smallest pebble sizes ( St = 0.05 ) we assumed, showing a path for planetesimal formation in vortex cores from even extremely subsolar metallicity. To estimate if the reached overdensities can be held together solely by their own gravity we estimate the Roche density at different radii. Depending on disk model and radial location of the pebble clump we do reach concentrations higher than the Roche density. We infer that if self-gravity was included for the pebbles then gravitational collapse would likely occur.

Electron trapping in ferroelectric HfZrO4 and Al- and Si-doped layers

Electron trapping in ferroelectric and non-ferroelectric HfO2-based layers was studied at room temperature by charge injection and photodepopulation techniques. The comparison of inferred energy distribution and density of trapped electrons in differently processed samples shows insignificant impact of Al- and Si-doping on trapping properties suggesting intrinsic nature of the observed traps. A comparison to the HfZrO4 layers is provided. The volume concentration of deep traps, most of which are energetically distributed between 2 and 3.5 eV below the HfO2 conduction band, is found to be in the range of 1019 cm−3.

Understanding temporal evolution of microstructures on metal-assisted chemically etched Ge surface and its applications

We report on metal-assisted chemical etching (MaCE) of single crystalline p-Ge(100) substrates at an elevated temperature, using dilute H2O2 solution, for various etching times in the range of 30–1200 s. We carry out atomic force microscopic and scanning electron microscopic studies to investigate the temporal evolution of microstructures on Ge substrates. It is observed that at lower etching times rough surfaces evolve, whereas higher etching times lead to the formation of pyramidally textured surfaces. In order to understand the present observations numerical simulation studies, based on continuum theory of stress-induced morphological instability, are carried out. Further, in an attempt to demonstrate the tunable multifunctional properties of pyramidally textured-Ge surfaces, we study light trapping and cold cathode electron emission properties of the same as a function of etching time. Interestingly, the optical reflectance of pyramidally textured surfaces reduces systematically with increasing etching time and the one evolved under an etching time of 1200 s can go down to an unprecedented low value of 0.23% over a broad spectral range (600–3000 nm). In addition, the turn-on potential for cold cathode electron emission from the etched-Ge surfaces also reduces steadily with increasing etching time with the lowest one being 1.7 V µm−1 (with the field-enhancement factor of 15,171) for the highest etching time of 1200 s. These are by far the best known results for any chemically etched-Ge surface and offer tremendous potential to fabricate various Ge-based optoelectronic devices.

Ternary fault permeability diagram: An innovative way to estimate fault zones hydraulics

Understanding the impact of fault zones on reservoir trap properties is a major challenge for a variety of geological resources applications. Fault zones in cohesive rocks are complex structures, composed of 3 components: rock matrix, damage zone fractures and fault core rock. Despite the diversity of methods to estimate fault zone permeability/drain properties, up to date none of them integrate simultaneously all three components, nor their evolution with time. In this paper, we present a ternary plot that characterizes the fault zones permeability as well as the drainage properties. The ternary plot aims at characterizing the fault zone permeability between the three vertices (matrix, fractures and fault core permeability) and at defining the drain properties among 4 possible hydraulic systems: (I) good horizontal and vertical, fault-perpendicular and -parallel; (II) moderate parallel fluid pathway; (III) good parallel fault-core and (IV) good parallel fractures. The ternary plot method is valid for 3 or 2 components fault zones. The application to the Castellas Fault field case study (SE France) shows the simplicity and efficiency of the plot for studying underground as well as cropping out active and/or fossil, simple or polyphase faults in reservoirs with complete or limited permeability data.

Enhanced light trapping in GaN thin films with Al nanoparticles for photocathode applications

In this paper, the light absorption model of GaN thin film with metal nanoparticle array is constructed based on COMSOL Multiphysics software, and the effect of metal nanoparticles on the light absorption performance of GaN thin film is studied. Compared with Au and Ag, Al nanoparticle array can enhance the absorption of ultraviolet light in GaN thin film, and the structure of Al nanoparticles deposited on the surface of GaN films has high light trapping properties. Therefore, Al nanoparticle array, as a method of improving the ultraviolet absorption performance of GaN, can provide some references for the design of ultraviolet photocathode, which will contribute to the development of high-efficient ultraviolet photocathode.