Trap Energy Research Articles

Exploring the inhibitory effect of WTaVCr high-entropy alloys on hydrogen retention: From dissolution, diffusion to desorption

Due to the excellent resistance to radiation damage, high-entropy alloys (HEAs) have been considered as important candidates for nuclear materials. However, to realize the great potential of HEAs in fusion energy, it is important to consider the hydrogen (H) behaviors, which remain to be elucidated. Here, we systematically investigate the dissolution, diffusion and desorption of H in equiatomic WTaVCr using the first-principles calculations. It is found that the H solution energy in WTaVCr is lower than that in pure W, which can be clarified by the H affinity of metallic elements and the available volume of interstitial sites. Accordingly, a possible diffusion path of interstitial H is selected, containing 26 metastable sites, and the corresponding energy barrier is 0.46 eV. Besides, the maximum trapping energy and accommodation number of H at a mono-vacancy in WTaVCr is only 0.30 eV and 3 ∼ 5 H, respectively, which is much lower than that in pure W (1.28 eV and 12 H). More importantly, because of the low trapping energy and moderate diffusion energy barrier, the desorption temperature of H from a mono-vacancy is lower than the room temperature, implying that vacancies are not efficient trapping centers for interstitial H atoms in WTaVCr. Therefore, although the equilibrium interstitial H concentration in WTaVCr is higher than that in pure W, H retention at high temperatures and H-induced blistering are suppressed due to the weak H-defect interactions. Our results will provide a good reference for understanding the H behaviors in HEAs.

Phonon-assisted leakage current of InGaN light emitting diode

We report on the leakage current mechanism in a blue GaN-based light-emitting diode (LED). The device structure was grown by the MOCVD technique on a sapphire substrate. The LED was characterized through various measurements including current-voltage, electroluminescence, and secondary ion mass spectroscopy (SIMS). Capacitance-voltage measurements were employed to calculate the depletion layer thickness at different bias voltages and to analyze the doping profile in the active layer. The reverse temperature-dependent current-voltage measurements were carried out to study the leakage mechanism. The leakage current was explained by phonon-assisted tunneling of charge carriers through deep trap states. The trap energy and density of states were extracted from the application of the introduced model. Cathodoluminescence measurements were performed to evaluate the density of dislocations, which were then compared to x-ray diffraction measurements. The determined value was close to the density of states obtained from the tunneling model.

Cluster dynamics modeling of hydrogen retention and desorption in tungsten with saturation and multi-trapping effect of sinks

Hydrogen (H) retention and desorption in tungsten (W)-based plasma-facing materials are still not well understood, largely due to the limitations of ex-situ observations in experimental detection methods like thermal desorption spectroscopy (TDS). In order to reveal the fundamental mechanisms behind H retention and desorption, we developed a cluster dynamics model, IRadMat-TDS, for theoretical modeling of depth distribution and TDS of deuterium (D) in polycrystalline W. The model newly includes the saturated absorption and emission of D in inherent sinks like grain boundaries (GBs), as well as the multi-trapping effect of D in various types of GBs with different trapping energies. The simulated TDS spectra are in agreement with experimental ones. For polycrystalline W under D ion irradiation within keV-energy range, two typical thermal desorption peaks in TDS at around 490 and 550 K are explicitly attributed to D emission from GBs and vacancies, respectively. And GBs play a major role in D retention. Moreover, the broad peaks in TDS come from the convolution of multi-trapping of D in sinks with different types of trapping sites rather than a single-site approximation.

The OrbiTOF mass analyzer: Time-of-flight analysis via an orbitrap quadro-logarithmic field with periodic drift focusing

Thermo Scientific™ Orbitrap™ analyzers represent a prominent class of high-resolution mass analyzer commonly used in life sciences, and for interrogation of complex samples. Injected ions, trapped within a quadro-logarithmic field, orbit a central electrode and oscillate up and down the axis. A new class of multi-reflection time-of-flight mass analyzer has been developed based on the Orbitrap field structure plus an additional series of periodic lenses wrapped around the central axis to constrain beam dispersion. The axial and angular velocity of the injected ions was balanced so that with each axial oscillation, the ions passed through the next lens in the series, to form a tightly folded 25-m long, 3-dimensional ion path, ending with ions striking a detector surface.Performance was interrogated via experiment and simulation. 70k resolving power was observed within the relatively compact analyzer, albeit at cost to transmission. A larger design with an integrated extraction trap and greater flight energy is discussed.

Reverse Leakage Current Hysteresis in GaN Schottky Barrier Diodes Interpreted in Terms of a Trap Energy Band

Reverse Leakage Current Hysteresis in GaN Schottky Barrier Diodes Interpreted in Terms of a Trap Energy Band

Understanding Electrophoresis and Electroosmosis in Nanopore Sensing with the Help of the Nanopore Electro-Osmotic Trap.

Nanopore technology is widely used for sequencing DNA, RNA, and peptides with single-molecule resolution, for fingerprinting single proteins, and for detecting metabolites. However, the molecular driving forces controlling the analyte capture, its residence time, and its escape have remained incompletely understood. The recently developed Nanopore Electro-Osmotic trap (NEOtrap) is well fit to study these basic physical processes in nanopore sensing, as it reveals previously missed events. Here, we use the NEOtrap to quantitate the electro-osmotic and electrophoretic forces that act on proteins inside the nanopore. We establish a physical model to describe the capture and escape processes, including the trapping energy potential. We verified the model with experimental data on CRISPR dCas9-RNA-DNA complexes, where we systematically screened crucial modeling parameters such as the size and net charge of the complex. Tuning the balance between electrophoretic and electro-osmotic forces in this way, we compare the trends in the kinetic parameters with our theoretical models. The result is a comprehensive picture of the major physical processes in nanopore trapping, which helps to guide the experiment design and signal interpretation in nanopore experiments.

Metastable Supramolecular Assembly of Simple Monomers Enabled by Confinement: Towards Aqueous Phase Room Temperature Phosphorescence

AbstractThe application of supramolecular assembly (SA) with room temperature phosphorescence (RTP) in aqueous phase has the potential to revolutionize numerous fields. However, using simple molecules with crystalline RTP to construct SA with aqueous phase RTP is hardly possible from the standpoint of forces. The reason lies in that the transition from crystal to SA involves a structure transformation from highly stable to more dynamic state, leading to increased non‐radiative deactivation pathways and silent RTP signal. Here, with the benefit of the confinement from the layered double hydroxide (LDH), various simple molecules (benzene derivatives) can successfully form metastable SA with aqueous phase RTP. The maximum of RTP lifetime and efficiency can reach 654.87 ms and 5.02 %, respectively. Mechanistic studies reveal the LDH energy trap can strengthen the intermolecular interaction, providing the prerequisite for the existence of metastable SA and appearance of aqueous phase RTP. The universality of this strategy will usher exploration into other multifunctional monomer, facilitating the development of SAs with aqueous phase RTP.

Metastable Supramolecular Assembly of Simple Monomers Enabled by Confinement: Towards Aqueous Phase Room Temperature Phosphorescence.

The application of supramolecular assembly (SA) with room temperature phosphorescence (RTP) in aqueous phase has the potential to revolutionize numerous fields. However, using simple molecules with crystalline RTP to construct SA with aqueous phase RTP is hardly possible from the standpoint of forces. The reason lies in that the transition from crystal to SA involves a structure transformation from highly stable to more dynamic state, leading to increased non-radiative deactivation pathways and silent RTP signal. Here, with the benefit of the confinement from the layered double hydroxide (LDH), various simple molecules (benzene derivatives) can successfully form metastable SA with aqueous phase RTP. The maximum of RTP lifetime and efficiency can reach 654.87 ms and 5.02 %, respectively. Mechanistic studies reveal the LDH energy trap can strengthen the intermolecular interaction, providing the prerequisite for the existence of metastable SA and appearance of aqueous phase RTP. The universality of this strategy will usher exploration into other multifunctional monomer, facilitating the development of SAs with aqueous phase RTP.

Deep trapped bipolar heterocharges enable electret nanofibrous membranes for high-efficiency PM0.3 filtration

Recently frequent global pandemic outbreak triggers the demand of high-efficiency aerosol filtration materials. Most of traditional electret air filters can hardly achieve high efficiency (>99.99 %) due to limited charge density and inappropriate charge distribution. The influence mechanism of nanofibers bipolar heterocharge configuration on electrostatic capture of airborne particles is still confusing. Herein, a novel strategy to create high-efficiency air filters based on electret nanofibrous membranes with deep trapped heterocharge is reported. Space charges and dipole charges with opposite polarity are formed in electrospun membranes composed of different polymers under in-situ charge injection and electric poling during electrospinning. Nanoscale spatial surface potential mapping on individual nanofiber characterized by Kelvin probe force microscopy demonstrates bipolar heterocharge distribution. Numerical simulation shows that fiber heterocharge distribution endows the electret membrane with greater electrostatic field intensity gradient, resulting in stronger electrostatic force between nanofibers and airborne particles. With bipolar heterocharge configuration and bimodal fiber diameter distribution, the nanofibrous membranes exhibit high-efficiency low-resistance filtration property against 0.3 μm NaCl particles (99.994 %, 97.4 Pa) at 5.3 cm s−1. Furthermore, benefiting from charges with deep trap energy of 1.12 eV, the membranes still maintain 99.972 % filtration efficiency after 40 h exposure in 95 % relatively humidity. The prepared membranes brings new insight in the design of high-efficiency and long-term stability air filtration materials for public health precaution. This study not only reveals influence mechanism of nanofibers heterocharge distribution on electrostatic attraction, but also provides useful guidance for fiber charge configuration design to improve aerosol filtration performance of electret filters.

Photocatalytic degradation of tetracycline hydrochloride and oxytetracycline using novel zinc-based coordination polymers constructed with mixed linkers

In the present work, a new zinc-based coordination polymer was successfully synthesized by mixed-ligand method with the molecular formula of {[Zn(ipa)(Hpap)]·2H2O}n, (abbreviated as Zn-CP), where ipa = isophthalic acid, Hpap = 4-(1H-pyrazol-4-yl)pyridine. Furthermore, reasonable characterization of Zn-CP was carried out by single crystal X-ray diffraction (SC-XRD), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and other spectra. During the characterization process, it was found that Zn-CP can have excellent acid-base stability, water stability and thermal stability. In addition, the complex was able to effectively degrade tetracycline hydrochloride (TCH) and oxytetracycline (OTC) within 60 min under visible light irradiation (with degradation efficiencies of 80.2 % and 83.5 %, respectively), and the cycling experiments showed that Zn-CP could still effectively degrade TCH and OTC after three cycles. Finally, in order to propose a rational photocatalytic degradation mechanism, free radical trapping experiments and energy band structure analysis were also carried out.

High‐Performance Self‐Powered Deep Ultraviolet Photodetector Based on NiO/β‐Ga2O3 Heterojunction with High Responsivity and Selectivity

A high‐performance self‐powered deep ultraviolet (DUV) photodetector based on the NiO/β‐Ga2O3 heterojunction is fabricated and analyzed. The NiO/β‐Ga2O3 heterojunction photodetectors are fabricated both with and without a post‐annealing process following NiO film deposition. Each photodetector structure is investigated through technology computer‐aided design simulations, including energy band diagram, trap density, and carrier concentration. The pristine self‐powered NiO/β‐Ga2O3 photodetector, lacking a post‐annealing process, exhibits partial Schottky contact formation between metal and NiO film, leading to performance degradation, including reduced responsivity, detectivity, and response time. On the other hand, the post‐annealed self‐powered NiO/β‐Ga2O3 photodetector demonstrates high performance such as a responsivity of 592.0 mA W−1, a detectivity of 4.30 × 1012 Jones, and response times of 30.93 ms and 72.32 ms, respectively. Therefore, the fabricated NiO/β‐Ga2O3 photodetector shows a promising potential for various applications requiring DUV detection without an external voltage bias.

Discrete trapping levels of localized states in amorphous silicon nitride

The spectrum of localized hole states (traps) in amorphous silicon nitride, a-Si3N4, is experimentally studied using the method of thermally stimulated depolarization. The experiment is compared with theoretical calculations using three models of the energy spectrum of traps: discrete spectrum (monoenergetic trap), continuous spectrum, and Gaussian trap distribution. The experiment is quantitatively described by a model of a discrete spectrum of traps with an energy of 1.15 eV and a width of no more than 0.01 eV. In the case of a continuous and Gaussian spectrum of traps, the contribution to depolarization is made by the deepest traps. The blurring of the trap energy level in a-Si3N4 due to the absence of long-range order (fluctuations in the Si–N bond length and fluctuations in the N–Si–N and Si–N–Si angles) does not exceed 0.01 eV.

Unveiling highly sensitive Dy3+ doped BaMgAl10O17 phosphor’s thermoluminescence trap features and temperature dependent luminescence for solid state lighting applications

This article explores the structural, morphological, thermoluminescence, and temperature-dependent emission properties of novel Dy3+ doped BaMgAl10O17(BAM-Dy) phosphors. Structural studies reveal that the phosphor has a similar structure to β-alumina. Rod-shaped interlinked surface morphology is a notable characteristic of the BAM-Dy samples. Incorporation of Dy3+ ions lead to the formation of distinct emission peaks (485 nm, 577 nm, and 635 nm) in the PL emission spectra. The effect of dopant concentration on the light output is crucial, and the highest PL intensity is observed for 1.5 mol% of Dy3+ concentration. The potential use of BAM-Dy phosphors for Gamma radiation detection and measurement is tested through thermoluminescence studies, which reveal high sensitivity, low threshold dose values, and exceptional response to low gamma doses, making them suitable for dosimetry applications. The investigation of trap parameters provides useful information about the number of traps, trapping mechanism, and trap energies, which is essential for in-depth study of synthesized phosphors for γ dosimetry application. The study of the effect of temperature on the luminescence behaviour is crucial for the application of phosphors in the light-emitting field. The BAM-Dy samples exhibit excellent thermal stability even at 210 °C, making them suitable for use in the field of White LEDs.

First principles study of the behavior of H atoms at TiO/V interface

TiO-precipitate and H atom are crucial factors for degradation of mechanical properties in vanadium alloys under irradiation environment. Herein, the behaviors of H atom at TiO/V interface are systemically studied by first principles calculations to elucidate the influence of TiO-precipitate on the H bubble formation. H atom prefers to dissolve in octahedral interstitial site (OIS2) with smaller lattice distortion and stronger bonds. The electronic interaction between H atom near monovacancy at the interface and surrounding atoms is enhanced with the existence of the TiO-precipitate. The capture of four H atoms in monovacancy is thermodynamically optimal, and the electronic action mainly contributes to the total trapping energy by monovacancy. The total trapping energy by multi-vacancy clusters is independent of the number of vacancies. H atoms trapped by vacancies cannot form H2 molecule at TiO/V interface. Our work can provide theoretical guidance for further understanding the H bubbles formation in vanadium alloys.

Strategies to Enhance the Stability of Non‐Fullerene Acceptor‐Based Organic Solar Cells

AbstractThrough comprehensive density functional theory calculations, the photodegradation mechanisms, including cis–trans isomerization, electrocyclization, and sigmatropic rearrangement reactions are investigated in indacenodithieno [3,2‐b] thiophene (IT)‐based non‐fullerene acceptors (NFAs). Various functional group substitutions on the core (fluorine, ethyl, and cyano groups) and end groups (fluorine) of NFA are introduced to elucidate the influence of chemical modifications on photodegradation pathways. The findings reveal that the core substitution can effectively suppress electrocyclization and 1,5‐sigmatropic shift reactions, which are major contributors to photodegradation. Furthermore, the electronic, excited‐state, and charge transport properties of pristine and degraded products are studied to gain insights into the impact of degradation on photovoltaic parameters. The results suggest that photodegradation leads to the formation of shallow energy trap states, hindering charge transport and increasing charge recombination, ultimately affecting the power conversion efficiency of organic solar cells (OSCs). The study not only provides a comprehensive understanding of photodegradation mechanisms but also offers valuable molecular design strategies to enhance the stability of NFAs for future large‐scale applications of OSCs. By establishing a clear connection between the chemical structure and photostability of NFA, this research represents a pivotal contribution to the field of organic electronics and sustainable energy technologies.

Mechanism and dynamic analysis of persistent luminescence in phosphors Sr2MgSi2O7: Eu2+, Dy3+

The persistent luminescent (PSL) phosphors Sr2-x-yMgSi2O7: xEu2+, yDy3+ (x = 0∼0.08, y = 0∼0.08) were synthesized by a solid-state reaction method in a weak reductive atmosphere of 5%-H2/N2. Comprehensive measurements were carried out to study the effects of Eu2+ and Dy3+ doping amount on the crystal phase, photoluminescence (PL), afterglow decay properties, and trap energy levels. The results indicated that the impurity phases decreased and disappeared, and crystalline grains tended to be larger and denser with the doping amount of Eu2+ and Dy3+ increasing. We shed light on the origination of asymmetric PL peak, concentration quenching of Eu2+ ions, time evolution of PSL specture and chromaticity of Eu2+, Dy3+ co-doped phosphors. Based on the deconvolutions of X-ray photoelectron spectroscopy (XPS) spectra and thermoluminescence (TL) spectra, the types and energy depth of traps in these phosphors were systematically studied. According to the data of PL, PLE, and TL, we deduced a schematic diagram of the energy level and discussed the mechanism of PSL of the phosphors. As Dy3+ dopant increases, the Eu2+, Dy3+ co-doped phosphors not only generate more defects of VO•• and VSrʺ, but also introduce DySr• defect with proper trap depth, meanwhile, a thermally assisted tunneling mechanism will gradually dominate during the persistent luminescence, which is responsible for that the phosphor with x = 0.02, y = 0.01 presents the best long afterglow property.

Analysis of interface trap induced ledge in β-Ga2O3 based MOS structures using UV-assisted capacitance–voltage measurements

A ledge feature in the capacitance–voltage (CV) profiles of Ga2O3 MOS (metal–oxide–semiconductor) capacitors is investigated using UV-assisted CV measurements. A model is presented whereby the capacitance ledge is associated with carrier trapping in deep-level states at the Al2O3/Ga2O3 interface. Following UV assisted emptying of interface traps at a constant bias, a voltage ramp toward flatband results in a CV ledge when the trap recombination current becomes equal to the quasi-static sweep charging current. The ledge continues until all the traps below the corresponding pinned surface potential have been filled. Varying the UV energy varies the ledge voltage range and allows a density of states to be determined as a function of energy. A broad interface state peak with maximum density ∼8 × 1012 cm−2 eV−1 for deep trap energies lying between 2.4 and 4.1 eV below the conduction band (CB) edge is extracted. Using the conductance method, the interface trap density is also found to rise toward the CB edge in the range 0.25–0.45 eV below the CB edge, reaching a maximum density of ∼1 × 1012 cm−2 eV−1. Combining these two techniques, an interface trap distribution is estimated for almost the entirety of the bandgap of Ga2O3. This novel technique probes deep interface states where standard methods fail to quantify interface states reliably.

Enhanced high‐temperature electrical properties and charge dynamics of inorganic/organic silicone elastomer nanocomposites via nanostructure grafting and molecular trap construction

AbstractThis study introduces a novel strategy to enhance the high‐temperature electrical performance of the silicone elastomer (SE), while ensuring control over its thermal and mechanical properties for SiC device packaging insulation application. For the same, the ultra‐low‐content inorganic/organic SE nanocomposites are prepared and tested (at room temperature and 150°C) by grafting polyhedral oligomeric silsesquioxane (POSS) nanofillers and doping organic semiconductors. It is found that grafting POSS nanofillers enhances the SE's thermal and mechanical properties. Moreover, doping the grafted SE with different organic semiconductors (ITIC, PCBM, and NTCDA) further improves its electrical properties and charge dynamics at 150°C. The optimal doping content for ITIC, PCBM, and NTCDA is found to be 0.05, 0.10, and 0.15 wt%, respectively. Among these, NTCDA exhibits superior electrical performance at 150°C. Particularly, compared to pure SE, NTCDA doping and POSS grafting reduce the electrical conductivity by an order of magnitude and increase the breakdown strength, charge hopping activation energy, and trap energy level by 65.5%, 0.20 eV and 0.73 eV, respectively. This study finds that organic semiconductors outperform nanostructures in inhibiting electron injection and immobilizing free electrons at high temperatures.Highlights Nano‐POSS grafting enhances material properties by reinforced molecular chains. Charge dynamics is studied by space charge and current integrated charge at HT. Organic semiconductors improve electrical properties and charge dynamics at HT. Organic semiconductors outperform nanofillers in immobilizing electrons at HT. The ideal organic semiconductor doping level correlates with its energy gap.

Phosphorescence of beta irradiated Sr4Al14O25:Eu2+,Dy3+ ─ A persistent luminescence phosphor

Phosphorescence of beta irradiated Sr4Al14O25:Eu2+,Dy3+ has been analysed. The persistent luminescence that defines this phosphor is phosphorescence hence the justification for this study. A set of phosphorescence decay curves were measured at various temperatures Tph between 20 and 352 °C following irradiation to 2 Gy. The residual thermoluminescence (R-TL) was recorded at 1 °C/s after the phosphorescence decay. A conventional TL glow curve recorded at the same rate following irradiation to 2 Gy produces two composite glow peaks P1 and P2 at 63 and 252 °C respectively. The decay curves measured between Tph = 28–60 °C and 200–240 °C associated with peaks P1 and P2 respectively give the values of the activation energy of peaks P1 and P2 as 0.59 ± 0.01 and 0.80 ± 0.04 eV. The effective frequency factors associated with the traps are 6.2 × 109 and 6.4 × 105 s−1 respectively. Peaks P1 and P2 are affected by thermal quenching with activation energy W = 0.69 ± 0.06 eV and 0.66 ± 0.03 eV respectively. The R-TL glow curves show two maxima R1 and R2 at ∼72 and 260 °C respectively. Kinetic analysis of R-TL peak R2 shows a Gaussian distribution of trap energy whereas the same analysis on R-TL peak R1 shows a non-Gaussian distribution of trap energy. The mean values of activation energy corresponding to the respective electron traps of R1 and R2 are estimated to be 0.62 ± 0.07 and 1.04 ± 0.06 eV. For peak R2, the Gaussian distribution curve shows the maximum at ∼1.06 eV which indicates that most electron traps corresponding to peak R2 have this trap depth.

Analysis of defects dominating carrier recombination in CeO2 single crystal for photocatalytic applications

In photocatalytic water splitting and CO2 reduction, recently, cerium oxide (CeO2) has been widely investigated. Defects that can directly dominate carrier recombination are essential for the photocatalytic performance of CeO2. In this study, several photoluminescence (PL) peaks are observed on the (100) face of an undoped CeO2 single crystal, indicating the presence of defects. Moreover, we characterize carrier recombination using time-resolved photoluminescence (TR-PL) and microwave photoconductivity decay (μ-PCD) measurements. The temperature dependence of decay curves is the result of carrier trapping and emission at deep levels. These decay curves are observed separately using a 565 nm band-pass filter (BPF) based on the PL spectra. The trap energy level ( ET ) and majority carrier capture cross-section ( σT ) of each defect are also analyzed using rate equations to fit the experimental results. The temperature-dependent time constants are well reproduced by a recombination model using hole traps HTinfrared and HTvisible at ET of 0.76 and 0.55 eV from the conduction or valence band, with estimated σT of the order of 10−21 and 10−22 cm2 for without and with the BPF, respectively. These findings regarding the presence of multiple defects in a single crystal indicate the necessity to focus on defect control.