Defect Profiles Research Articles

Numerical Simulation of OXIDE-ION Blocking Effect in Hydrogen Permeable Metal-Supported Fuel Cell

Protonic ceramic fuel cells (PCFCs) have been drawing considerable attentions because of their potential for high-power operating at intermediate temperature (IT), 400–600°C, which is a salient issue for their practical implementation. BaZr0.1Ce0.7Y0.2O3, popular proton-conducting ceramic electrolyte material, has notably high conductivity of 9 × 10−3 S cm−1 at 500°C [1], but vast majority of power outputs in current PCFC literature still lag far behind 1.0 W cm−2 at the IT regime. In general, PCFCs have structure of porous anode support composed proton-conducting ceramic electrolyte and metallic Ni. Meanwhile, a hydrogen membrane fuel cell (HMFC), which consist of a dense hydrogen-permeable metal anode and kindred electrolyte material, has achieved extraordinary performances of 1.4 W cm−2 at 600°C [2]. This is higher than any others ever reported to the best of our knowledge. However, what give rise to such high performance is obscure. Here, we simulated effect of oxide-ion blocking at anode/electrolyte on defect profile in HMFC and compared them with those of PCFCs to elucidate origins of the high performance.The one-dimensional concentration profiles of three charged defect carriers: oxygen vacancy, proton, and oxygen hole at steady state were computed based on Nernst–Planck–Poisson model with defect thermodynamics of BaZr0.8Y0.2O3 [3]. In PCFC, membrane is equilibrated with O2, H2, and H2O gases. In HMFC, however, boundary conditions at the anodic surface are unknown since the surface is sealed by dense metal anode. We made an assumption that a flux of oxygen vacancy is kept at 0 inside the electrolyte membrane of HMFC [4].Simulations confirm that oxide-ion blocking at an electrolyte/anode interface greatly modifies the defects’ distribution across the membrane. Positively charged oxygen vacancies are depressed near electrolyte/anode interface owing to the oxide-ion blocking, and thus, protonic defects are alternatively accumulated near the regions for the charge neutrality preservation, which results in the enhancement of local proton conductivity (Attached image). Accordingly, the superior performance of HMFC to PCFC is attributable the proton pumping by utilizing the oxygen chemical potentials.

ALS motor neurons exhibit hallmark metabolic defects that are rescued by SIRT3 activation

Motor neurons (MNs) are highly energetic cells and recent studies suggest that altered energy metabolism precede MN loss in amyotrophic lateral sclerosis (ALS), an age-onset neurodegenerative disease. However, clear mechanistic insights linking altered metabolism and MN death are still missing. In this study, induced pluripotent stem cells from healthy controls, familial ALS, and sporadic ALS patients were differentiated toward spinal MNs, cortical neurons, and cardiomyocytes. Metabolic flux analyses reveal an MN-specific deficiency in mitochondrial respiration in ALS. Intriguingly, all forms of familial and sporadic ALS MNs tested in our study exhibited similar defective metabolic profiles, which were attributed to hyper-acetylation of mitochondrial proteins. In the mitochondria, Sirtuin-3 (SIRT3) functions as a mitochondrial deacetylase to maintain mitochondrial function and integrity. We found that activating SIRT3 using nicotinamide or a small molecule activator reversed the defective metabolic profiles in all our ALS MNs, as well as correct a constellation of ALS-associated phenotypes.

A nonlinear dynamic vibration model of a defective bearing: the importance of modelling the angle of the leading and trailing edges of a defect

Rolling element bearings eventually become worn and fail by developing surface defects, such as spalls, dents and pits. Previous researchers have tested bearings with defects that have sharp rectangular edges that were used to develop analytical models of a defective bearing. These models have limitations that require smooth surfaces and constant curvature of the bearing components; as well as assuming the defect profile. A method has been created to capture the surface topography of a bearing defect. A numerical model has been developed for a rolling element bearing that uses the measured defect profile and removes the limitations of models by previous researchers that use analytical expressions for contact area and force. The predicted vibration response of a bearing with a defect that has sloped leading and trailing edges on the outer and inner raceway was compared with experimental results. It was found that the new numerical model was able to predict the vibration response of a defective bearing. The defect topographies and the developed model have been made publicly available.

Defect depth-profiling in kesterite absorber by means of chemical etching and surface analysis

A method to probe the depth morphology, defect profile and possible secondary phases in a thin film semiconductor is presented, taking a standard Kesterite film as an example. Using a top-down approach based on a previously reported controlled Methanol-Br2 chemical etching, well-defined slabs of a state of the art Kesterite absorber are fabricated. The analysis of their morphology both by Scanning Electron Microscopy and 3D optical Profilometry reveals the extent of a previously reported poor film morphology toward the back interface, and we are able to determine that more than 50% of a standard absorber is disconnected from the substrate. More importantly, these etched films are subsequently analyzed by surface sensitive techniques such as X-ray Photoelectron Spectroscopy and UV-Raman analysis. An accurate composition profile is established, and for the first time, a direct observation of the defects’ nature and their depth profiling in Kesterite is made possible. While VCu are found with a constant amount throughout the absorber, indicating a homogenous carrier concentration, a prevalence of the ZnSn defect is observed with a steep gradient toward the back interface, associated with an increase in the SnSe2 secondary phase. With bulk defects being often pointed out as the intrinsic limitation of this material, this result highlights what possibly is the main impediment of Kesterite solar cells, and a critical point to address in the design of future devices. Beyond the case of Kesterite absorbers, the method presented here offers a combination of simplicity, tunability and versatility making a straightforward transfer to other emerging thin film absorbers feasible, and it could possibly be an important tool in their future performance assessment and comparison.

Якість програмного забезпечення: моделі оцінювання доцільності засіву та життєвий цикл профілю дефектів

Забезпечення якості програмного забезпечення (ПЗ) є невід'ємною частиною процесу його розроблення. Першочерговим завданням забезпечення якості ПЗ є його оцінювання. Відомий підхід до оцінювання якості ПЗ заснований на засіві відповідних дефектів. Використання такого підходу, з одного боку, зумовлено наявністю в міжнародних стандартах вимог до його застосування у критичних інформаційних системах, а з іншого – практикою компаній-розробників ПЗ, які приймають рішення про потребу застосування методу засіву дефектів, тому часто його використовують. В обох випадках передбачається наявність додаткових ресурсів, якими повинна володіти компанія-розробник ПЗ. У роботі запропоновано модель для оцінювання доцільності застосування методу засіву дефектів ПЗ і модель життєвого циклу профілю дефектів ПЗ. Модель для оцінювання доцільності застосування методу засіву дефектів ПЗ містить такі елементи: константа необхідності розрахунку доцільності оцінювання якості ПЗ, автоматизація етапу, обсяг об'єкта оцінювання, обсяг дефектів, що засіваються. Профіль дефектів ПЗ подано таксономією і множинами дефектів ПЗ, які відповідають їх таксономічним типам. Розглянуто таксономію типів дефектів у вигляді ієрархічної та фасетної структур. У межах зазначеного життєвого циклу профіль дефектів ПЗ, як правило, модифікується у вигляді таких типів профілів: прогнозований профіль, профіль дефектів, що засіваються, профіль всіх виявлених дефектів при тестуванні після засіву, профіль нових виявлених при тестуванні (на додаток до засіяних) дефектів, профіль виявлених засіяних дефектів і профіль невиявлених засіяних дефектів. Під час оцінювання якості ПЗ сформовані типи профілів його дефектів аналізують, обчислюють метрики і на підставі оцінок отриманих неув'язок приймається рішення про рівень якості ПЗ. Усі неув'язки дефектів профілів подано поєднанням таких типів профілів дефектів ПЗ: профіль дефектів, що засіваються, профілі усіх виявлених дефектів та відповідної таксономії типів дефектів.

Defect incorporation in In-containing layers and quantum wells: experimental analysis via deep level profiling and optical spectroscopy

Recent studies demonstrated that the performance of InGaN/GaN quantum well (QW) light emitting diodes (LEDs) can be significantly improved through the insertion of an InGaN underlayer (UL). The current working hypothesis is that the presence of the UL reduces the density of non-radiative recombination centers (NRCs) in the QW itself: during the growth of the UL, surface defects are effectively buried in the UL, without propagating towards the QW region. Despite the importance of this hypothesis, the concentration profile of defects in the quantum wells of LEDs with and without the UL was never investigated in detail. This paper uses combined capacitance-voltage and steady-state photocapacitance measurements to experimentally identify the defects acting as NRCs and to extract a depth-profile of the traps, thus proving the incorporation upon indium-reaction. Specifically: (i) we demonstrate that LEDs without UL have a high density (9.2 × 1015 cm−3) of defects, compared to samples with UL (0.8 × 1015 cm−3); (ii) defects are located near midgap (E C-1.8 eV, corresponding to E i-E T ∼ 0.3 eV), thus acting as efficient NRCs; (iii) crucially, the density of defects has a peak within the QWs, indicating that traps are segregated at the first grown InGaN layers; (iv) we propose a model to calculate trap distribution in the QW, and we demonstrate a good correspondence with experimental data. These results provide unambiguous demonstration of the role of UL in limiting the propagation of defects towards the QWs, and the first experimental characterization of the properties of the related traps.

A More Accurate Reconstruction Method for Detecting Large-Depth Defects in Plates Using SH Guided Waves

The inspection of thickness thinning defects and corrosion defects is greatly significant for the health prediction of plate structures. The main aim of this research is to propose a novel and effective approach to achieve the accurate and rapid detection of arbitrary defects using shear horizontal (SH) guided waves, particularly for large-depth and complex defects. The proposed approach combines the quantitative detection of Fourier transform with a reference model-based strategy to improve the accuracy of large-depth defect detection. Since the shallow defect profile is theoretically constructed by inverse Fourier transform of the product of reflection coefficients and integral coefficients of reference models, the unknown large-depth defect can be initially assessed using the relevant information from a predefined reference model. By iteratively updating the integral coefficients of reference models, the accuracy of reconstruction of large-depth defects is much improved. To achieve the converged defect profile, a termination criterion, the root mean square error, is applied to guarantee the construction of defects with a high level of accuracy. Moreover, the hybrid finite element method is used to simulate the propagation of SH guided waves in plates for calculating the reflection coefficients of plates with defects. Finally, to demonstrate the capability of the developed reconstruction method for defect detection in terms of accuracy and efficiency, three types of large-depth defect profiles, i.e., a rectangular flaw, a double-rectangular flaw and a complex flaw, are examined. Results show that the discrepancy between the predicted defect profile and the real one is quite small, even in the largest-depth defect case where the defect depth is equal to 0.733 times the plate thickness, the minimal difference is observed. It is noted that the fast convergence of the proposed approach can be achieved by no more than ten updates for the worst case.

Profile reconstruction of a local defect in a groove structure and the theoretical limit under the vector diffraction theory.

The profile of a fine local defect in a periodic surface relief structure is reconstructed from a scattered wave. This defect cannot be imaged with an optical imaging system owing to the diffraction limit, and complicated multiscattering among the high-aspect-ratio grooves and the defect makes it difficult to reconstruct the profile using the scalar diffraction theory. We propose and numerically demonstrate a reconstruction algorithm by applying an efficient vector analysis method-the difference-field boundary element method. We also classify the profile according to the difficulty of reconstruction, which depends on the observation system and the noise level. Finally, this analysis provides the accuracy and limit of reconstruction under the vector diffraction theory.

Multi-mode hydrodynamic evolution of perturbations seeded by isolated surface defects

Inherently multi-mode evolution of isolated defects, such as straight grooves and axisymmetric dots on planar laser targets, is studied theoretically. The development of perturbations is considered for a propagating rippled shock front, a material interface subject to the classical Richtmyer–Meshkov instability (RMI), a rippled rarefaction wave produced by the feedout process, an ablation front subject to the ablative RMI, and a thin fluid layer subject to the classical Rayleigh–Taylor instability (RTI). For the small-amplitude regime, we have established specific characteristics of the perturbation evolution initiated with such defects, scaling, and conservation laws governing it. The main features of the nonlinear growth of the classical and ablative RTI starting from isolated defects are the lateral expansion of the bubbles and the oblique with respect to the direction of the acceleration, ejection of spikes. It results in filling up the void left from the bubble growth by the laterally converging spike material. This effect, first discovered in simulations by Dahlburg et al. [Phys. Fluids B 5, 571 (1993)], and very recently observed by Zulick et al. [Phys. Rev. Lett. 125, 055001 (2020)], is captured by the appropriate modification of the Ott–Basko thin-layer classical RTI theory for arbitrary defect profiles. Predictions for novel hydrodynamic experiments on multi-mode hydrodynamic perturbation evolution are presented.

Hybrid laser and air-coupled ultrasonic defect detection of aluminium and CFRP plates by means of Lamb mode

This study presents two non-contact systems – hybrid laser with air-coupled ultrasound and pure air-coupled ultrasonic system for the non-destructive inspection and detection of flaws in CFRP and aluminium plates. B-scans are used to identify the size and location of the defects. The defects are detected through changes in amplitude of the waves passing through them. B-scans, represented as intensity graphs, clearly show the changes in the defect profiles. In addition, there is agreement between the experimental values of the diameter of the defect and the measured values. The two systems and configurations are tested and compared in order to determine their effectiveness in defect identification. The results of this study prove the potential of these non-destructive and non-contact systems for defect detection in aluminium and CFRP composites.

High power factor due to multi-scale engineering in ultra-thin bismuth telluride films

High thermoelectric (TE) power factors were obtained for bismuth telluride by deploying confinement and multi-scale engineering in synergy. The thickness of the film was kept in the ultra-thin range (41 nm) following which a high magnitude of 1.9 × 104 S m−1 was obtained at room temperature (RT). Films were deposited at an elevated substrate temperature to enhance the grain quality and high mobility bearing (00l) grain growth. Thus, relatively large crystallite sizes (∼26 nm) with less grain boundaries and directional growth with a low defect profile were the prime reasons for highly enhanced electrical conductivity. Apart from the multiple effects that were deployed, ultra-thin dimensions of the films proved to be effective in further enhancing Seebeck coefficient values. The co-alloyed In minimized the hole concentration through reducing antisite defects and also preserved the reduced bipolar effect at elevated temperatures. The inclusion of excess tellurium induced Te segregates in the film that helped in energy dependent scattering of carriers in addition to its donor-like effect. Hot carrier filtering, induced by excess Te along with ultra-thin dimensions resulted in a Seebeck coefficient (S) of −223.6 μV K−1 at RT. A soaring value of −338.1 μV K−1 was obtained at 90 °C. Following the synergetic employment of multiple enhancement strategies, a high power factor of 959.9 μW m−1 K−2 was obtained at room temperature with a towering magnitude of 2537.7 μW m−1 K−2 at 90 °C.

Boundary layer turbulence statistics over transitionally rough marine fouling control coatings

The results of a dedicated boundary layer measurement campaign, which was conducted by using a 2D LDV system over transitionally rough and irregular marine surfaces in a large flow-channel, are presented and discussed in this study. The experimental campaign aimed to investigate the turbulence statistics for zero-pressure gradient turbulent boundary layers developed over marine fouling control coatings, which represent transitionally rough and irregular surfaces, along with hydraulically smooth and fully-rough reference surfaces. A particular emphasis was placed on the wall outer layer similarity. At the same time, the main characteristics of the boundary layer flow such as the velocity defect profiles, Reynolds stresses, triple correlations of turbulence velocities, skewness distributions and flatness factors were comparatively discussed for six different surfaces. The surface roughness properties, boundary layer characteristic parameters, wake parameters and frictional drag properties were also presented for the tested surfaces along with their roughness functions. The outer layer similarity was observed for the surfaces coated with the fouling control coatings in general. The current study presented, perhaps for the first time in such details, the higher-order statistics of turbulence for the turbulent boundary layer flow developed over the state-of-the-art marine fouling control coatings.

Defect shape detection and defect reconstruction in active thermography by means of two-dimensional convolutional neural network as well as spatiotemporal convolutional LSTM network

ABSTRACT A neural network (NN) for semantic segmentation (U-Net) was used for the detection of crack-type defects from thermography sequences. For this task, data sequences of forged steel parts were acquired through induction thermography and the corresponding phase images calculated. The results for defect detection were quantitatively evaluated using Intersection over Union (IoU) metric. Further, a combination of 2D convolutional layer as well as LSTM (Long-Short-Term-Memory) is shown, which includes three-dimensional aspects in the form of time dependent and spatial changes and allows a defect shape reconstruction of back wall drillings. Therefore, pulsed thermography sequences were simulated with COMSOL Multiphysics. Finally, the reconstruction results were compared with the ground-truth defect profile using Mean Squared Error (MSE). The approaches provide improvements over conventional methods in non-destructive testing using infrared thermography.

An analytical approach to reconstruction of axisymmetric defects in pipelines using T(0, 1) guided waves

Torsional guided waves have been widely utilized to inspect the surface corrosion in pipelines due to their simple displacement behaviors and the ability of longrange transmission. Especially, the torsional mode T(0, 1), which is the first order of torsional guided waves, plays the irreplaceable position and role, mainly because of its non-dispersion characteristic property. However, one of the most pressing challenges faced in modern quality inspection is to detect the surface defects in pipelines with a high level of accuracy. Taking into account this situation, a quantitative reconstruction method using the torsional guided wave T(0, 1) is proposed in this paper. The methodology for defect reconstruction consists of three steps. First, the reflection coefficients of the guided wave T(0, 1) scattered by different sizes of axisymmetric defects are calculated using the developed hybrid finite element method (HFEM). Then, applying the boundary integral equation (BIE) and Born approximation, the Fourier transform of the surface defect profile can be analytically derived as the correlative product of reflection coefficients of the torsional guided wave T(0, 1) and the fundamental solution of the intact pipeline in the frequency domain. Finally, reconstruction of defects is precisely performed by the inverse Fourier transform of the product in the frequency domain. Numerical experiments show that the proposed approach is suitable for the detection of surface defects with arbitrary shapes. Meanwhile, the effects of the depth and width of surface defects on the accuracy of defect reconstruction are investigated. It is noted that the reconstructive error is less than 10%, providing that the defect depth is no more than one half of the pipe thickness.

Neutron irradiation and forming gas anneal impact on β-Ga2O3 deep level defects

We used depth-resolved cathodoluminescence spectroscopy (DRCLS), absorption spectroscopy, and temperature-dependent Hall effect (TDH) measurements to study the effects of fluence dependent neutron irradiations on deep level defects and the associated changes of electrical properties of β-Ga2O3 grown by low pressure chemical vapor deposition and pulsed laser deposition. DRCLS enabled us to monitor systematic increases of three deep level defects after neutron irradiation which correlated with TDH measurements of significant free carrier removal and mobility decrease. The correlations between defect profiles and electrical property changes vs. irradiation dose link these dominant electrically active native point defects in Ga2O3 with their contributions to free carrier mobility, carrier density, and donor/acceptor depth profiles, further revealing their donor/acceptor electrical behavior and physical nature, consistent with the formation of compensating defects. After irradiation, temperature-dependent forming gas (FG) anneals were performed to reverse the radiation-induced damage and carrier removal. The evolution of defect concentrations with increasing neutron dose and their depth-resolved distributions with FG anneal temperature reveal an interplay between specific defects to control electronic properties.

Lateral Profiling of Defects and Charges in Oxide Semiconductor Channel Thin-Film Transistors

The lateral distributions of free carriers and defects in a channel of top gate In-Ga-Zn-O thin-film transistors were extracted using a single pulse charge pumping method. A square pulse was applied to the gate, while the charge transport current was monitored at the source–drain. A transmission line model was used to confirm the charging mechanism and extract the effective charge length. The time dependence of the trapped charge density was determined by comparing the charging and discharging transient characteristics. The lateral profiles of the free carriers and defects were decoupled successfully using the time dependence of the effective charge length, free charges, and trapped charges.

Low-Energy Muons as a Tool for a Depth-Resolved Analysis of the SiO<sub>2</sub>/4H-SiC Interface

In this work, the potential of muon spin rotation (μSR) with low-energy muons (LE-μ) for the investigation of oxidation-induced defects at the SiO2/4H-SiC interface is explored. By using implantation energies for the muons in the keV range and comparing the fractions of muonium in different regions, the depth distribution of defects in the first 200 nm of the target material can be resolved. Defect profiles of interfaces with either deposited or thermally grown SiO2 layers on 4H-SiC are compared. The results show an increased number of defects in the case of a thermal oxide, both on the oxide and on the SiC side of the interface, with a spatial extension of a few tens of nm.

Influence of Hysteresis Effect on Contrast of Welding Defects Profile in Magneto-Optical Image

Under the excitation of alternating magnetic field, the disadvantage of Magneto-optical Imaging (MOI) Non-destructive Testing (NDT) is no obvious difference between the light and shade of micro defects (sub-surface cracks) image. It will lead to great difficulties in feature extraction and recognition of welding defects. In response to this problem, the magneto-optical image (induced magnetic field) characteristics of welding defects under an alternating magnetic field are examined in this study. The variation of induced magnetic fields of different welding defects (cracks, pits, unfused, etc.) is studied by simulation and MOI to optimize the nondestructive detection of MOI under alternating excitation. Both the simulation experiment and the MOI detection experiment are conducted to study the variation of the induced magnetic field under the excitation frequency of 50 Hz and sampling frequency of 75 frames/s. First, the variation law of the induced magnetic field for the welding defect is analyzed by simulation. Then, by studying the color moments of different defect magneto-optical image data sets, the periodic variation of the same defect magneto-optical image under alternating excitation is analyzed. To prove the correctness of the periodic law summarized by the color moment, the cosine similarity is used to test the periodic variation of the image. The results show that the contrast of welding defects on the magneto-optical image changes periodically. According to this rule, the image with the strongest contrast is selected in magneto-optical image data set for defect feature extraction and recognition to overcome its shortcomings.

Channel Defect Profiling and Passivation for ZnO Thin-Film Transistors.

The electrical characteristics of Zinc oxide (ZnO) thin-film transistors are analyzed to apprehend the effects of oxygen vacancies after vacuum treatment. The energy level of the oxygen vacancies was found to be located near the conduction band of ZnO, which contributed to the increase in drain current (ID) via trap-assisted tunneling when the gate voltage (VG) is lower than the specific voltage associated with the trap level. The oxygen vacancies were successfully passivated after the annealing of ZnO in oxygen ambient. We determined that the trap-induced Schottky barrier lowering reduced a drain barrier when the drain was subjected to negative bias stress. Consequentially, the field effect mobility increased from 8.5 m2 V−1·s−1 to 8.9 m2 V−1·s−1 and on-current increased by ~13%.

Congenital Heart Defects and Dysmorphic Facial Features in Patients Suspicious of 22q11.2 Deletion Syndrome in Southern Brazil.

22q11.2 deletion syndrome (22q11.2DS) is considered one of the most frequently observed chromosomal abnormalities in association with congenital heart disease (CHD), which can also include some combination of other features. Thus, the aim of this work was to verify the profile of dysmorphic features and heart defects found in patients referred to a reference center in Southern Brazil with clinical findings suggestive of 22q11.2DS. In the overall sample group, only patients with dysmorphic facial features (skull, eyes, ear, and nose) associated with CHD (obstructive pulmonary valve ring, truncus arteriosus, and bicuspid aortic valve associated with atrial septal defect and/or right aortic arch) had a 22q11.2 deletion. These findings proved to be reliable clinical criteria for referral to perform fluorescent in situ hybridization investigation for 22q11.2 deletion.