Trapping Characteristics Research Articles

Deep Traps in AlN Hydride Vapor Phase Epitaxy Film on Low-Temperature AlN/Sapphire

Deep trap states were examined in c-plane, Al-polar AlN epilayers, deposited via metal organic chemical vapor deposition on 270 nm thick AlN buffer layers on sapphire substrates. Contacts were created using e-beam deposited Ni through a shadow mask, with I-V characteristics revealing a trapped limited current (TLC) regime and voltage-dependent hysteresis upon light-emitting diode illumination. Thermally stimulated current and photothermal ionization current spectroscopy measurements demonstrated a prominent trap activation energy of approximately 0.75 eV and additional trap energies of 0.6, 0.4, 0.25, 1.05, and 1.1 eV. The observed differences in photocurrent responses between forward and reverse biases suggest that forward bias induces electron trapping at deeper levels, influencing the TLC behavior. Comparisons with bulk n-type AlN crystals from previous studies show similarities in deep trap spectra, suggesting commonality in trap characteristics across different AlN samples.

Thermoluminescence (TL) properties of Eu3+ incorporated with CaB4O7 phosphors prepared by solution-combustion process

The solution-combustion approach was used to create CaB4O7:Eu3+phosphors using Ba (NO3)2, Eu (NO3)3·5H2O, H3BO3, NH3(ON)H2, and NH4NO3 as source materials. We investigated the thermoluminescence (TL) characteristics of beta (β)-irradiated CaB4O7:Eu3+. When the TL intensity was evaluated at different dosages of β, it rose with the dose. Changes in peak temperature were observed because of the investigation of the effects of varying heating rates on TL glow curves. Moreover, the positions of the peak temperature and the TL intensity did not change when the same sample was measured again, suggesting that the sample was stable. Additionally, the study calculated several kinetic parameters, including activation energy (E), frequency factor (s), and geometrical factor (μg), for distinct TL glow curves. Through geometric analysis of TL glow peaks, the study determined activation energies and kinetic orders, enabling the calculation of the frequency factor. The findings highlight the suitability of the prepared phosphor for dosimetry and provide insights into trap characteristics crucial for continuous illumination at room temperature. The study also emphasises the importance of optimising trap depth for prolonged afterglow, shedding light on the interplay between trap energies and luminescence characteristics. These findings deepen our comprehension of phosphor behavior and open the door to better dosimetry applications.

Effect of ash-bridge deposition in asymmetric diesel particulate filter channels on the pressure drop and particulate matter trapping characteristics

A diesel particulate filter (DPF) is commonly used to trap particulate matter (PM). The collapse and sintering of carbon and ash deposits during exhaust gas flow and DPF regeneration frequently result in the formation of ash bridges, which are buildups of ash and PM that clog the filter channels. To investigate the impact of an ash bridge formed by accumulated ash on the pressure drop and PM trapping characteristics of asymmetric DPFs, an asymmetric DPF channel with an ash bridge was constructed. The analysis employed computational fluid dynamics to examine how the ash bridge affects the pressure drop and PM trapping characteristics in an asymmetric DPF. This study reveals that the asymmetric DPF design effectively enhances the ash-holding capacity, thereby mitigating the risk of channel blockage. The presence of ash bridges in DPF channels has a more substantial impact on the pressure drop through radial congestion than through axial congestion. The application of asymmetric thin-wall DPFs can counteract the increase in exhaust backpressure caused by ash bridges. An ash bridge located in the middle of a DPF channel intensifies the uneven deposition of PM. However, implementing an asymmetric DPF structure enhances the uniformity of PM deposition.

Dual microwave frequency modulation of the VCSEL injection current for a CPT-based atomic clock.

Previously, we have proposed a method to control the emission spectrum of the vertical-cavity surface-emitting laser (VCSEL) with the synchronized modulation of the injection current at single and doubled frequencies. In this work, the above method is used to improve the metrological characteristics of the coherent population trapping (CPT) resonance in 87Rb. The dual-frequency (DF) modulation reduces the carrier power and suppresses the light shift of the resonance frequency, if it is unattainable with the single-frequency modulation. In addition, a higher resonance contrast is achieved by equalizing the powers of the resonant components of the spectrum.

Preparation and anti-counterfeiting application of Sr3Y2Ge3O12:Bi2+ red long afterglow luminescent

Red, as one of the three primary colors, is crucial for blending the luminescent color of long-lasting materials. This project selected Sr3Y2Ge3O12 as the substrate and Bi2+ as the activator. A solid-state method at high temperature was used to prepare a new type of visible red long-afterglow luminescent material, by adjusting the doping concentration of Bi2+ and changing the calcination temperature. When the doping concentration of Bi2+ was 0.50mol% and the calcination temperature was 1150 °C, the prepared Sr3Y2Ge3O12:Bi2+ had the best luminescent properties. After being excited by 254 nm ultraviolet light, the material shows the red afterglow luminous intensity, duration and stability that meet the practical application requirements. Through thermoluminescence, photoluminescence and fluorescence spectra, the trap characteristics and internal mechanism of long afterglow were studied comprehensively. Finally, the film and printing ink were prepared by using the Sr3Y2Ge3O12:Bi2+ long afterglow luminescent powder with the best luminescent performance, and the pattern anti-counterfeiting was successfully realized.

Bioinspired Artificial Visual-Respiratory Synapse as Multimodal Scene Recognition System with Oxidized-Vacancies MXene.

In the pursuit of artificial neural systems, the integration of multimodal plasticity, memory retention, and perceptual functions stands as a paramount objective in achieving neuromorphic perceptual components inspired by the human brain, to emulating the neurological excitability tuning observed in human visual and respiratory collaborations. Here, an artificial visual-respiratory synapse is presented with monolayer oxidized MXene (VRSOM) exhibiting synergistic light and atmospheric plasticity. The VRSOM enables to realize facile modulation of synaptic behaviors, encompassing postsynaptic current, sustained photoconductivity, stable facilitation/depression properties, and "learning-experience" behavior. These performances rely on the privileged photocarrier trapping characteristics and the hydroxyl-preferential selectivity inherent of oxidized vacancies. Moreover, environment recognitions and multimodal neural network image identifications are achieved through multisensory integration, underscoring the potential of the VRSOM in reproducing human-like perceptual attributes. The VRSOM platform holds significant promise for hardware output of human-like mixed-modal interactions and paves the way for perceiving multisensory neural behaviors in artificial interactive devices.

Degradation analysis of GaN-based high–electron-mobility transistors under different stresses in semi-on state conditions

The large numbers of high-energy carriers that occur in semiconductor devices under semi-on state conditions can cause significant device degradation. The effects of different stresses on the electrical and trapping characteristics of GaN-based high-electron-mobility transistors (HEMTs) are investigated. Test results for GaN HEMTs under semi-on state conditions show that the electrical characteristics of these devices degrade to a certain extent after they are subjected to electrical pulse stress cycles with different drain voltage, frequencies, and duty cycles; a degree of degradation also occurs in the electrical characteristics of the devices when they are subjected to direct current electrical stresses. After electrical stress is applied, the absolute amplitude of the traps in the device increases, thus indicating an increase in the trap density. The results show that voltage is the main driver for device damage, with the current playing an accelerating role through its effects on device temperature or by supplying hot electrons; therefore, the drain voltage has the most significant effect on device degradation, which is mainly due to channel high-energy hot electron injection.

Thickness-derived optical-electrical management in Sn-based perovskite solar cells

Tin-based perovskite solar cells (TPSCs) have attracted great attention due to their promising photovoltaic performance and environmental friendliness. Adequate photon trapping and efficient carrier utilization are known to be the keys to achieving high-performance devices, which are closely related to the thickness of the light-absorbing layer and the quality of film formation, respectively. Due to the ultra-fast crystallization characteristics and low defect formation energy, thick tin-based perovskite films are faced with poor electrical performance due to poor quality. Thin tin-based perovskite films are easy to achieve low defects and high crystallization quality, but insufficient thickness leads to the problem of insufficient light trapping. To address these issues, we have thoroughly investigated the various aspects of the photoelectric conversion process in TPSC devices and, for the first time, explored the behavior of front-end optical field management. It is found that the self-constructed microcavity effect can effectively improve the light trapping efficiency under the premise that a thin light-absorbing layer is used, so that sufficient photon trapping and excellent carrier transport characteristics can be ensured simultaneously to realize a high-performance device. Different from the traditional film formation and defect modulation strategy, the present work provides a feasible idea for the performance enhancement of TPSC devices, and is also of great significance for cost control and environmental protection issues in commercial applications.

Microscopic characteristics of CO2 residual trapping in saline aquifers: Experimental study based on X-ray microtomography

The occurrence form and migration characteristics of CO2 in pores have a direct impact on CO2 residual trapping and the safety of CO2 sequestration. In this work, we conduct core flooding and CT scanning experiments at different permeabilities, brine salinities, and sodium dodecyl sulfate (SDS) concentrations. We measure the CO2-brine-rock contact angles in situ and quantitatively analyze the microscopic characteristics of CO2 residual trapping in the pores. The experimental results indicate that CO2 primarily occurs in the form of network, cluster, and droplet. The efficiency of CO2 residual trapping is closely linked to the pore structure, with a higher permeability resulting in less effective trapping. Furthermore, an increase in salinity weakens the hydrophilicity of the sandstone, while the addition of SDS enhances it. The higher the SDS concentration, the greater the sandstone hydrophilicity. When the sandstone hydrophilicity is enhanced, the efficiency of CO2 residual trapping also increases. Additionally, a low permeability, low salinity, and high SDS concentration all result in 20%–35% increase in the frequency of CO2 network formed in the pores, which is advantageous for CO2 residual trapping. These findings clarify the possible occurrence forms of gaseous CO2 in the pores and their variations under different conditions and are also expected to help establish methods for improving CO2 residual trapping efficiency to enhance the long-term safety of CO2 sequestration in shallow saline aquifers.

Influence of Thermal Aging on Space Charge Characteristics and Electrical Conduction Behavior of Cross-Linked Polyethylene Cable Insulation.

The aging of cable insulation presents a significant threat to the safe operation of cables, with space charge serving as a crucial factor influencing cable insulation degradation. However, the characteristics related to space charge and conduction current behavior during thermal aging remain unclear. This study focused on the thermal aging of cross-linked polyethylene (XLPE) material and utilizes a combined pulse electro-acoustic (PEA) and conduction current testing system to analyze the space charge and conduction current characteristics in the sample under varying electric fields and temperatures. The average charge density, short-circuit residual electric field, electric field distortion rate, and conduction current were studied. The findings indicate that the space charge in the samples following thermal aging is predominantly governed by the injected charge. The amorphous region of XLPE decreases, while the cross-linking degree increases after aging, thereby facilitating charge carrier migration within the sample and reducing the generation of charge carriers through thermal pyrolysis. The minimum temperature required for charge injection is reduced by thermal aging. Furthermore, modifications in conduction current, residual electric field, and average charge density indicate that thermal aging has the potential to alter the microstructure and trap characteristics of XLPE. This study provides empirical evidence to elucidate the underlying mechanism of cable insulation aging.

LiGa5O8: Fe3+: A novel and super long near-infrared persistent material

The development of near-infrared persistent materials has become a popular research area owing to their diverse applications. However, the efficient emitters for these materials remains limited. Cr3+ is one of the strongest candidates, since it displays better performance with long duration. Fe3+ is a potential nontoxic alternative although its performance is not as good as Cr3+. In this study, a series of novel Fe3+-activated near-infrared long afterglow phosphors of LiGa5O8 have been prepared. Photoluminescence and persistence luminescence spectroscopy have been collected to investigate its optical properties. Furthermore, the trap characteristics of the samples were systematically analyzed by collecting thermoluminescence signals. The results indicate that there is an intense near-infrared emission centered at 675 nm and a long afterglow duration of more than 28 h for the optimized sample. Trap analysis indicates that oxygen vacancy defects are not the primary reasons for the extraordinarily long afterglow in these samples. Instead, the interaction of other trap types, such as antisite defects, probably contribute to the excellent afterglow properties of the material.

Increased Deep Trap Density in Interfacial Engineered Nanocomposite Revealed by Sequential Kelvin Probe Force Microscopy for High Dielectric Energy Storage.

Nanocomposites combining inorganic nanoparticles with high dielectric constant and polymers with high breakdown strength are promising for the high energy density storage of electricity, and carrier traps can significantly affect the dielectric breakdown process. Nevertheless, there still lacks direct experimental evidence on how nanoparticles affect the trap characteristics of nanocomposites, especially in a spatially resolved manner. Here, a technique is developed to image the trap distribution based on sequential Kelvin probe force microscopy (KPFM) in combination with the isothermal surface potential decay (ISPD) technique, wherein both shallow and deep trap densities and the corresponding energy levels can be mapped with nanoscale resolution. The technique is first validated using the widely-used commercial biaxially oriented polypropylene, yielding consistent results with macroscopic ISPD. The technique is then applied to investigate polyvinylidene fluoride-based nanocomposites filled with barium titanate nanoparticles, revealing higher deep trap density around surface-modified nanoparticles, which correlates well with its increased breakdown strength. This technique thus provides a powerful spatially resolved tool for understanding the microscopic mechanism of dielectric breakdown of nanocomposites.

Technical note: Characterization of a single-beam gradient force aerosol optical tweezer for droplet trapping, phase transition monitoring, and morphology studies

Abstract. Single particle analysis is essential for a better understanding of the particle transformation process and to predict its environmental impact. In this study, we developed an aerosol optical tweezer (AOT) Raman spectroscopy system to investigate the phase state and morphology of suspended aerosol droplets in real time. The system comprises four modules: optical trapping, reaction, illumination and imaging, and detection. The optical trapping module utilizes a 532 nm laser and a 100 × oil immersion objective to stably trap aerosol droplets within 30 s. The reaction module allows us to adjust relative humidity (RH) and introduce reaction gases into the droplet levitation chamber, facilitating experiments to study liquid–liquid phase transitions. The illumination and imaging module employs a high-speed camera to monitor the trapped droplets, while the detector module records Raman scattering light. We trapped sodium chloride (NaCl) and 3-methyl glutaric acid (3-MGA) mixed droplets to examine RH-dependent morphology changes. Liquid–liquid phase separation (LLPS) occurred when RH was decreased. Additionally, we introduced ozone and limonene/pinene to generate secondary organic aerosol (SOA) particles in situ, which collided with the trapped droplet and dissolved in it. To determine the trapped droplet's characteristics, we utilized an open-source program based on Mie theory to retrieve diameter and refractive index from the observed whispering gallery modes (WGMs) in Raman spectra. It is found that mixed droplets formed core–shell morphology when RH was decreased, and the RH dependence of the droplets' phase transitions generated by different SOA precursors varied. Our AOT system serves as an essential experimental platform for in situ assessment of morphology and phase state during dynamic atmospheric processes.

The clinical characteristics of neutrophil extracellular trap in patients with severe cerebral venous sinus thrombosis and its prognostic value in acute and subacute patients

Objective: To explore the clinical characteristics of neutrophil extracellular trap (NET) in patients with severe cerebral venous sinus thrombosis (CVST) and to study their prognostic value in the acute and subacute phases. Methods: This study is a retrospective case series analysis. Clinical and pathological data of 52 patients with severe cerebral venous sinus thrombosis who underwent endovascular treatment in the Department of Neurosurgery, Tianjin Huanhu Hospital from June 2019 to June 2022 were retrospectively analyzed. There were 20 males and 32 females, with an age of (40.1±13.6) years(range:18 to 66 years). Forty-five healthy physical examinees were included in the control group. High-resolution MRI was used to stage the thrombus, with 11 cases in the acute group, 28 cases in the subacute group, and 13 cases in the chronic group. Thrombus specimens were obtained through endovascular treatment, and the fluorescence intensity of NET in peripheral blood at different time points was analyzed by immunofluorescence contrast,including the double-stranded DNA structure and adhesion protein components (citrolinated histone H3 (CitH3), myeloperoxidase-DNA complex(MPO-DNA), neutrophil elastase (NE)). The NET markers were determined by ELISA. Spearman rank correlation analysis was used to analyze the correlation between the NET markers in peripheral blood of patients with severe cerebral venous sinus thrombosis in the acute and subacute phases and the volume of venous sinus thrombus, the degree of venous sinus recanalization after treatment, and the discharge modified Rankin scale(mRS)score. The accuracy of NET markers in predicting the prognosis of patients with severe cerebral venous sinus thrombosis was analyzed by drawing receiver operating characteristic (ROC) curve and calculating the area under the curve (AUC). Results: The results of immunofluorescence staining and ELISA showed that no NET structure was formed in the peripheral blood of the control group, while CitH3, MPO-DNA and NE levels in the peripheral blood of CVST patients were increased, among which the acute stage group was the highest, followed by the subacute group, and the chronic group was the lowest. Spearman correlation analysis showed that CitH3, MPO-DNA and NE levels in peripheral blood of patients in acute group and subacute group were positively correlated with thrombus volume and mRS score at discharge (P<0.05). The levels of CitH3 and MPO-DNA in peripheral blood of patients with complete venous sinus recanalization were lower than those of patients with partial venous sinus recanalization (P<0.01). ROC curve analysis results showed that MPO-DNA and NE had no predictive ability for the prognosis of CVST patients (P values were 0.614 and 0.324, respectively), and the AUC of CitH3 was 0.800 (95%CI: 0.638~0.962, P=0.032), the best cut-off value was 13.5 μg/L, the sensitivity was 100%, and the specificity was 58.8%. Conclusions: A large number of NET are formed in patients with severe cerebral venous sinus thrombosis in acute stage. Patients with severe cerebral venous sinus thrombosis in acute stage and subacute stage with high peripheral blood NET content has a low rate of complete sinus revascularization and poor neurological function recovery after treatment.

Improving the thermostatic steam trap characteristics using spring elements with the shape memory effect

The object of research is the deformation-force characteristics of spring elements of thermostatic steam traps with the shape memory effect. The research solves the problem related to the imperfection of the design of steam traps controlling elements and their high inertia. Experimental studies on the impact of the spring force elements cooling rate on the deformation-force characteristics were conducted. Experimental studies showed that the significant impact of the spring force elements cooling rate on the deformation-force characteristics is observed exceptionally under the deformation mode at a temperature t ≤ Мf. Based on the results of the experiments, it was found that decreasing the cooling rate from 66.7 to 0.013 °C/s has a positive effect on the spring element deformation-force characteristics. Distinctive feature of the work is the study of winding pitch and thermal force cycling impact on the deformation-force characteristics of spring elements. It was found that using thermal force cycling makes it possible to reduce the force required for complete compression of the spring element by 60 %. Intensive decrease in the force required for the complete compression of the spring elements occurs during the first 100 thermal force cycles. The rational method for spring elements heat treatment has been given. It is based on the next steps: heating to a temperature of 400–500 °C for 1 hour; exposure at this temperature for an hour; cooling with rate 0.013 °C/s, the number of thermal force cycles is at least 100 with a winding pitch of 8·10–3 m. Based on research results, an improved design of thermostatic steam trap with controlling element in the form of cylindrical compression spring made of the VSP-1 alloy based on nitinol has been presented

Effects of gamma-ray irradiation on material and electrical properties of AlN gate dielectric on 4H-SiC

This article investigates the radiation effects on as-deposited and annealed AlN films on 4H-SiC substrates under gamma-rays. The AlN films are prepared using plasma-enhanced-atomic-layer-deposition on an n-type 4H-SiC substrate. The AlN/4H-SiC MIS structure is subjected to gamma-ray irradiation with total doses of 0, 300, and 600 krad(Si). Physical, chemical, and electrical methods were employed to study the variations in surface morphology, charge transport, and interfacial trapping characteristics induced by irradiation. After 300 krad(Si) irradiation, the as-deposited and annealed samples exhibit their highest root mean square values of 0.917 nm and 1.190 nm, respectively, which is attributed to N vacancy defects induced by irradiation. Under irradiation, the flatband voltage (V fb) of the as-deposited sample shifts from 2.24 to 0.78 V, while the annealed sample shifts from 1.18 to 2.16 V. X-ray photoelectron spectrum analysis reveals the decomposition of O-related defects in the as-deposited AlN and the formation of Al(NO x ) y compounds in the annealed sample. Furthermore, the space-charge-limits-conduction (SCLC) in the as-deposited sample is enhanced after radiation, while the barrier height of the annealed sample decreases from 1.12 to 0.84 eV, accompanied by the occurrence of the SCLC. The physical mechanism of the degradation of electrical performance in irradiated devices is the introduction of defects like N vacancies and O-related defects like Al(NO x ) y . These findings provide valuable insights for SiC power devices in space applications.

Change in Hydrogen Trapping Characteristics and Influence on Hydrogen Embrittlement Sensitivity in a Medium-Carbon, High-Strength Steel: The Effects of Heat Treatments.

Medium-carbon, high-strength steels are widely used in the field of hydrogen energy because of their good mechanical properties, and they can be readily tailored by heat treatment processes such as the normalizing-tempering (N&T) and quenching-tempering (Q&T) methods. The hydrogen embrittlement (HE) susceptibility of a medium-carbon, high-strength steel was investigated utilizing microstructural characterization with scanning electron microscopy (SEM), the electron backscatter diffraction (EBSD) technique, and transmission electron microscopy (TEM). A study was also conducted on the steel's hydrogen transport behavior as affected by the N&T and Q&T treatments. The steel contained more hydrogen traps, such as dislocations, grain boundaries, lath boundaries, and carbide interfaces, after the Q&T process, which was associated with a lower HE sensitivity when comparing the two treatments. In comparison, the N&T process produced larger-size and lesser-density carbides distributed along the grain boundaries, and this resulted in a relatively higher HE susceptibility, as revealed by the slow-strain-rate tensile (SSRT) tests of the hydrogen-charged steels and by the fractographic study of the fracture surface.

Miniature atom bottle traps enabled by chiral doughnut light

We highlight what we believe to be a novel optical set-up which enables the confinement of cold atoms in a finite set of sub-wavelength bottle traps. This involves two counter-propagating vortex beams with the same winding number ℓ = ±1 and the same circular polarization (. Strong focusing generates significant longitudinal field components which become responsible for an on-axis standing wave enabling the axial confinement of far blue-detuned atoms. The off-axis radial confinement is provided by the optical potential due to the transverse components of the light. The trap characteristics are illustrated using experimentally accessible parameters and are tunable by changing the power, focusing and ellipticity of the light. Atoms trapped in such a set-up are useful for applications, including quantum simulation and quantum information processing.

Insights into dynamic switching behavior and electric field distribution of depletion-mode GaN HEMT with bonding pad over active layout

Bonding pad over active (BPOA) layout, which stacks traditional horizontal structure pad electrodes vertically above the active area, is an area-effective device architecture and packaging-enabled solution for GaN-based high electron mobility transistors (HEMTs). In this work, the dynamic switching and electric field distribution of such layout, as well as associated capacitance–voltage and trapping characteristics, are comprehensively studied on D-mode GaN-on-sapphire HEMT by performing numerical simulations. In terms of different pad electrodes covering the active area, BPOA is composed of various structures such as gate-related and drain-related BPOAs (i.e. G-BPOA and D-BPOA), among which G-BPOA exhibits inferior switching characteristics due to the additional introduction of Miller capacitance that prolongs the device switching, while breakdown voltage of D-BPOA is 400–900 V lower than other BPOA counterparts due to the interplay between D-BPOA and the drain electrode. Furthermore, the effects of trap capture cross section and trap density on switching characteristics are evaluated. These results highlight the differences in electrical characteristics of various structures within the BPOA layout, and provide valuable insights into BPOA device design and performance improvement.

Emission and capture characteristics of deep hole trap in n-GaN by optical deep level transient spectroscopy

Emission and capture characteristics of a deep hole trap (H1) in n-GaN Schottky barrier diodes (SBDs) have been investigated by optical deep level transient spectroscopy (ODLTS). Activation energy (E emi) and capture cross-section (σ p) of H1 are determined to be 0.75 eV and 4.67 × 10−15 cm2, respectively. Distribution of apparent trap concentration in space charge region is demonstrated. Temperature-enhanced emission process is revealed by decrease of emission time constant. Electric-field-boosted trap emission kinetics are analyzed by the Poole−Frenkel emission (PFE) model. In addition, H1 shows point defect capture properties and temperature-enhanced capture kinetics. Taking both hole capture and emission processes into account during laser beam incidence, H1 features a trap concentration of 2.67 × 1015 cm−3. The method and obtained results may facilitate understanding of minority carrier trap properties in wide bandgap semiconductor material and can be applied for device reliability assessment.