Single Defect Research Articles

Energetics of Point Defects in D0a Ag3Sn: First‐Principles Calculations

The Ag3Sn intermetallic compound is commonly found and acts as a strengthening factor in the key lead‐free solders based on Sn‐Ag‐Cu. The Ag3Sn phase exhibits also an asymmetric off‐stoichiometry, which necessitates the existence of constitutional point defects. The presence of point defects can, in general, sensitively affect the plastic deformation of materials and the strengthening role of Ag3Sn in particular. To understand the nature of the point defects and the compositional stability of Ag3Sn, the relaxed structures and the energies of single point defects (vacancies and antisite defects) in all three sublattices of Ag3Sn are calculated at 0 K using ab initio density functional theory (DFT) and the supercell method. The first‐principles‐based calculations predict that the AgSn antisite defect (Ag substitution for Sn) has the smallest enthalpy of formation, thus indicating that the AgSn antisite defect is the dominant point defect in Ag3Sn. The point defect concentrations as a function of Sn content are estimated using the DFT defect energies and the Wagner–Schottky model. The compositional dependence of the point defect concentrations gives new insights on the atomistic mechanisms of formation of nonstoichiometric Ag3Sn.

Rate theory model of irradiation effects in UO2: Influence of electronic energy losses

To investigate the effect of electronic energy losses on nuclear damage in UO2, we use a simple Rate Theory (RT) model, based on the time evolution of single point defects, governed by their absorption at the surface of TEM lamellae, and by interstitial-type dislocation loops nucleation, solely characterized by their number and average size. We first parametrize the model by fitting six different experimental datasets at various temperatures, ion type and energy (0.39 MeV Xe and 4 MeV Au ion irradiations at 93, 298 and 873 K) where defect evolution in UO2 is dominated by displacement damage caused by nuclear energy losses. The model suggests that dislocation evolution kinetics is driven by monomers diffusion at 873 K. At lower temperature (93 and 298 K) monomer diffusion has little impact and the evolution is governed by the nucleation of loops within the collision cascade. Analysis of four additional experimental datasets at 93 and 298 K where electronic energy losses are strong (single 6 MeV Si and dual simultaneous Xe & Si ion irradiations) required modification of monomer's diffusion coefficients. In the case of single Si ion irradiation, evolution is temperature independent and the enhanced diffusion due to electronic excitations and ionizations are best captured by adding athermal component to the monomer diffusion coefficients. In case of the dual Xe & Si ions irradiation, electronic excitation caused by Si ions impacts the defects pre-generated by Xe ions and enhances defect diffusion by at local heating induced by the thermal spike of Si ions. This effect is best captured by artificially raising the irradiation temperature.

High-efficiency treatment of oily wastewater by photocatalytic in-situ Fenton oxidation under visible light

Oily wastewater poses a significant threat to environmental safety, and complex water environments have caused numerous disturbances in oil pollution treatment. Therefore, constructing composite systems is expected to improve oil pollution treatment efficiency. This study developed an efficient photocatalytic in-situ Fenton oxidation system, HTCC@ZnFe2O4/Ag3PO4 (HZFA), loaded onto polypropylene spheres (PP) for treating oily wastewater (diesel oil) in complex environments. The built-in electric field of HZFA promotes photogenerated carrier separation, enhancing photocatalytic effect. At a diesel concentration of 3.2 g/L, performance of HZFA degraded diesel in deionized water and artificial seawater (ASW) were 60.80 % and 52.62 %, respectively, much higher than a pure photocatalytic system (13.84 %). The dual system compensated for single system defects like instability and narrow application range, achieving 8 effective cycles in ASW. Experimental and computational results showed that high oxidation and reduction potentials in the dual system promoted hydrocarbon oxidative degradation and H2O2 production/activation. The amount of OH, O2−, and h+ produced in different environments is fundamental for the stabilization of catalytic degradation by HZFA. GC–MS and DFT analysis revealed potential oxidative chain-breaking processes for diesel components like alkanes, aromatics, alcohols, acids, aldehydes, and esters. This study offers a new method for green and efficient oily wastewater treatment, overcoming inherent defects of traditional Fenton, with broad application prospects.

Image reconstruction from compressed measurements for ultrasound NDT

In ultrasound NDT, Delay-and-Sum schemes are commonly used to reconstruct images from the measurement data. For single channel pulse-echo measurements, this is called Synthetic Aperture Focusing Technique (SAFT). In a multi-channel setup, SAFT is extended to the Total Focusing Method (TFM), where the focused image is reconstructed from measurements of all transmit-receive combinations, called Full Matrix Capture (FMC). In previous work, we showed that both SAFT and TFM can be cast as a sparse recovery problem that enables enhancing the Delay-and-Sum scheme to a physically motivated forward model that leads to improved image quality. The reconstruction is performed using l1 minimization. Further, this also allows to perform the reconstruction from compressed/subsampled measurements following compressed sensing theory. This subsampling was achieved by only measuring a subset of the frequency coefficients of the signal. In both the single channel and the multi-channel setup the amount of measurement data is thereby significantly reduced. Additionally, for the TFM, we added a spatial subsampling by only considering a subset of transmit and receive pairs, further reducing the measurement data and at the same time also reducing the measurement time. In our previous work, the frequency and spatial dimensions were considered separately for simplicity, using the same compression strategy for all spatial measurements. In this work we consider joint frequency/spatial compression schemes. We show that a joint multidimensional compression strategy where different Fourier subsets are considered for each channel pair leads to a superior reconstruction performance when the compression rate is fixed. Analysis based on an analytical model for a single defect and a real-world example with multiple defects shows that the approach works in practice.

Threefold Impact on Reaction Coordinate Mapping of Zirconium Based Tri‐Chalcogenide Pseudo‐Monolayers as Emerging Ultrathin Catalysts for Water Splitting

AbstractThe continuous quest of finding optimum catalysts for photo‐electrocatalytic (PEC) water splitting has been revolving around 2D ultrathin materials because of the fact of exploiting both the surface area. In this work, a threefold impact is envisaged route to enhance the activity both in terms of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the emerging Zirconium Tri‐sulfides (ZrS3) based pseudo‐monolayers. Due to the unique and distinct electronic properties of the tri‐chalcogenide systems as compared to the di‐chalcogenide counterpart of Zirconium, one could afford to explore the implications of not only single‐atom functionalization and vacancy defect, but also the external strain to expedite the bifunctional catalytic activity in this promising material. Rigorous electronic structure calculations have been performed for the mentioned threefold effect on not only the band‐edge alignment, but going beyond to it by further constructing the reaction coordinate mapping corresponding to HER and OER mechanism. The repercussion of external strain in addition to the single atom functionalization and vacancy defect on the adsorption free energies of the prime intermediates of HER and OER reaction has been further correlated with the work function variation in this pseudo‐monolayer system.

Imaging Quantum Interference in a Monolayer Kitaev Quantum Spin Liquid Candidate

Single atomic defects are prominent windows to look into host quantum states because collective responses from the host states emerge as localized states around the defects. Friedel oscillations and Kondo clouds in Fermi liquids are quintessential examples. However, the situation is quite different for quantum spin liquid (QSL), an exotic state of matter with fractionalized quasiparticles and topological order arising from a profound impact of quantum entanglement. Elucidating the underlying local electronic property has been challenging due to the charge neutrality of fractionalized quasiparticles and the insulating nature of QSLs. Here, using spectroscopic-imaging scanning tunneling microscopy, we report atomically resolved images of monolayer α−RuCl3, the most promising Kitaev QSL candidate, on metallic substrates. We find quantum interference in the insulator manifesting as incommensurate and decaying spatial oscillations of the local density of states around defects with a characteristic bias dependence. The oscillation differs from any known spatial structures in its nature and does not exist in other Mott insulators, implying it is an exotic oscillation involved with excitations unique to α−RuCl3. Numerical simulations suggest that the observed oscillation can be reproduced by assuming that itinerant Majorana fermions of Kitaev QSL are scattered across the Majorana Fermi surface. The oscillation provides a new approach to exploring Kitaev QSLs through the local response against defects like Friedel oscillations in metals. Published by the American Physical Society 2024

Structural integrity assessment of pipe elbows: Burst test and finite element analysis

In this study, the failure pressures of pipe elbows were compared with those predicted using Level 3 numerical assessment method (Finite Element Method). Four 90-degree pipes elbows representing a pristine pipe, a pipe with a single corrosion defect, a pipe with longitudinally aligned interacting defects, and a pipe with a circumferentially aligned interacting defects, were subjected to internal pressure based on the ASME B31.3–2012 Burst Test standard until failure. The Sch-80 pipes were made of ASTM A234 WPB steel with a wall thickness and bending radius of 12.7 mm and 305 mm respectively. The corrosion defects were simulated on the exterior surface of the pipe elbows using computer numerical control (CNC) machine to generate a machined version of the corrosion defect. The results revealed that corrosion defects significantly reduce the burst pressure of pipe elbows, with longitudinally aligned interacting defects causing the largest reduction of 20.9 % compared to pristine pipe. The comparison between the Level 3 numerical assessment method and burst test showed close agreement with a maximum difference of 4.79 %, confirming the accuracy and reliability of the numerical method.

One-Stone-for-Multiple-Birds Additive Strategy for Highly Efficient and Stable Carbon-Based Hole-Transport-Layer-Free CsPbI2Br Solar Cells.

During fabrication and operation of perovskite solar cells (PSCs), defects commonly arise within the crystals as well as at grain boundaries. However, conventional additive strategies typically only serve to mitigate the occurrence of a single defect and fail to significantly enhance device performance. Herein, carbon-based hole-transport-layer-free CsPbI2Br devices are focused on, one kind of important PSCs with more stable structure and an appropriate bandgap for a semitransparent solar cell or a top cell in a tandem configuration, and present a highly efficient one-stone-for-multiple-birds additive strategy based on lanthanide trifluoromethanesulfonates (Ln(OTF)3, Ln: neodymium (Nd), europium (Eu), dysprosium (Dy), thulium (Tm)). Density functional theory calculations reveal that the Ln3+ ions with a smaller radius can elevate defect formation energy for Pb and I vacancies within the crystals, while the presence of OTF- can effectively passivating uncoordinated Pb2+ at grain boundaries. In addition, Ln(OTF)3 addition increases the grain size and meanwhile reduces the surface roughness of the CsPbI2Br layers. All these positive contributions lead to a significant enhancement in power conversion efficiency (PCE) to 15.13% which is among the top PCEs reported for the corresponding solar cells, from 11.80% of the pristine device without Tm(OTF)3 addition, while notably boosting long-term stability and reducing current-voltage hysteresis.

Research on the fusion imaging method of sign coherence and time reversal for Lamb wave sparse array

Time-reversal imaging struggles to detect plate-like structures due to interference from Lamb wave mode conversion and the processing demands, leading to less effective outcomes. This paper proposes a sign coherence factor and time reversal fusion (SCF-TR) imaging method based on amplitude and phase estimation. This method removes the coherence of array signals during signal reversal and refocusing. It reintroduces the sign coherence component to reduce interference from non-target scattered waves and partially overcome the constraints imposed by the Rayleigh criterion. The method allows imaging at a resolution smaller than the wavelength of Lamb and enhances the quality of the resulting images. In addition, a sparse array design utilizing the White Shark Optimisation Algorithm (WSO) is proposed to streamline the SCF-TR calculation process. This design utilizes sparse full matrix data to improve imaging efficiency. The experimental results show that for single blind hole defects, the SCF-TR method improves the array performance metrics and signal-to-noise ratio by 22.46% and 42.50%, respectively, compared to the TR method. For multiple asymmetric blind hole defects, when the defect size exceeds the resolution threshold, SCF-TR accurately reflects the position and morphology of defects smaller than the wavelength. When the defect size is below the resolution threshold, SCF-TR achieves super-resolution imaging. The sparse array designed using the White Shark Optimization algorithm demonstrates good sidelobe characteristics, effectively reducing sidelobe noise without reducing the array aperture. Moreover, the SCF-TR imaging time is reduced by approximately half while maintaining imaging accuracy.

Optical induction of monopoles, knots, and skyrmions in quantum gases

Single topological defects and related structures have been experimentally created inside clouds of Bose-Einstein condensates. However, a practical protocol for creating multiple defects inside a single cloud—a prerequisite for studying defect interactions—has been lacking. Here we propose, and theoretically analyze, a practical protocol for the creation of configurations of topological monopoles, quantum knots, and skyrmions in Bose-Einstein condensates by employing fictitious magnetic fields induced by the interaction of the atomic cloud with coherent light fields. It is observed that a single coherent field is not enough for this purpose, but instead we find incoherent superpositions of several coherent fields that introduce topological point charges. We numerically estimate the experimentally achievable strengths and gradients of the induced fictitious magnetic fields and find them to be adjustable at will to several orders of magnitude greater than those of the physical magnetic fields employed in previous experimental studies. This property together with ultrafast control of the optical fields paves the way for advanced engineering of topological defects in quantum gases. Published by the American Physical Society 2024

Consanguinity and Occurrence of Monogenic Diseases in a Single Tertiary Centre in Riyadh, Saudi Arabia: A 2 Years Cross-Sectional Study.

Consanguinity, or the practice of marrying close relatives, is a common cultural tradition in Saudi Arabia, with rates among the highest in the world. This practice has significant implications for the prevalence and distribution of major single genetic defects and chromosomal abnormalities within the Saudi population. Herein, using the BESTCare electronic medical record system (designed to streamline hospital operations, enhance patient care, and improve the overall efficiency of healthcare services; bestcare.ezcaretech.com) in a single tertiary centre, King Abdullah Specialized Children Hospital (KASCH) in Riyadh, Saudi Arabia, we performed a cross-sectional study for all patients referred to the hospital from the 1st January 2020 until 1st January 2022. The present study, which included 1100 individuals, found a high prevalence of consanguinity (64%) and a significant proportion of third-degree relatives (69%). The mean age of participants was 12.24 years, and the diagnostic rate using advanced molecular genetics techniques was 45%, with whole exome sequencing (WES) being the most common method (43%). The study also noted a significant delay in diagnosis for more than a year in 16% of cases, with a common neurodevelopmental phenotype (18%). In conclusion, we revealed the prevalence of consanguineous marriages in the KASCH hospital in Riyadh, Saudi Arabia. We also highlighted the most frequently referred phenotype. These findings are consistent with previous research on the prevalence and impact of consanguinity on rare genetic disorders.

Characterization of hexagonal boron nitride quantum emitters for application in quantum radiometry

Abstract We present the metrological characterization of single-photon emitters based on single point defects in hexagonal boron nitride (hBN) to be used in quantum radiometry. The characterization is performed in terms of their spectral characteristics, single-photon properties and stability of photon flux emission at room temperature. A statistical analysis of 563 emitters has been carried out showing that approximately one third of the photon emission can be attributed to single photon emitters. In addition, a relative calibration of two single-photon avalanche diode (SPAD) detectors using a selected hBN single-photon emitter is presented.

Neuroimaging Applications for the Delivery and Monitoring of Gene Therapy for Central Nervous System Diseases.

Neurological disease due to single gene defects represents a targetable entity for adeno-associated virus (AAV) mediated gene therapy. The delivery of AAV-mediated gene therapy to the brain is challenging, owing to the presence of the blood-brain barrier. Techniques in gene transfer, such as convection-enhanced intraparenchymal delivery and image-guided delivery to the cerebrospinal fluid (CSF) spaces of the brain has led the field into highly accurate delivery techniques, which provide correction of genetic defects in specific brain regions or more broadly. These techniques commonly use magnetic resonance imaging (MRI), computed tomography (CT), and fluoroscopic guidance. Even more, the neuroimaging changes evaluated by MRI, MR spectroscopy (MRS), diffusion tensor imaging (DTI), and functional MRI (fMRI) can serve as important biomarkers of therapy effect and overall disease progression. Here, we discuss the role of neuroimaging in delivering AAV vectors and monitoring the effect of gene therapy.

Atomic-Level Defect Engineering in GeP Nanoflake Biosensors for Gastric Cancer Diagnosis.

Defect engineering offers a promising approach to enhance the sensitivity of biosensing materials by creating abundant chemically active sites. Despite its potential, achieving precise control and modification of these defects remains a significant challenge. Herein, we propose atomic-level defect engineering in GeP two-dimensional (2D) layered materials, following precise in situ growing Au nanoparticles on the single defect active sites for the design of ultrasensitive biosensors. The GeP-based biosensor exhibits notable capabilities for miRNA detection with excellent chemical stability, sensitivity, selectivity, and an extremely low detection limit of 28.6 aM. When applied to clinical tissue samples from gastric cancer patients, the biosensor effectively quantified the miR378c biomarker, enabling accurate stage-specific monitoring. This research not only represents a crucial advancement in the field of biosensing materials through defect engineering but also provides a promising avenue for early cancer diagnosis, staging, and monitoring.

Quantum Spin Probe of Single Charge Dynamics.

Electronic defects in semiconductors form the basis for emerging quantum technologies, but many defect centers are difficult to access at the single-particle level. A method for probing optically inactive spin defects would reveal semiconductor physics at the atomic scale and advance the study of new quantum systems. We exploit the intrinsic correlation between the charge and spin states of defect centers to measure the charge populations and dynamics of single substitutional nitrogen spin defects in diamond. By probing their steady-state spin population, read out at the single-defect level with a nearby nitrogen vacancy center, we directly measure the defect ionization-corroborated by first-principles calculations-an effect we do not have access to with traditional coherence-based quantum sensing.

Genetic analysis of the X-linked Adrenoleukodystrophy ABCD1 gene in Drosophila uncovers a role in Peroxisomal dynamics.

X-linked adrenoleukodystrophy (X-ALD) is a progressive neurodegenerative disorder caused by a loss-of-function (LOF) mutation in the ATP-binding cassette subfamily D member 1 (ABCD1) gene, leading to the accumulation of very long-chain fatty acids (VLCFAs). This disorder exhibits striking heterogeneity; some male patients develop an early childhood neuroinflammatory demyelination disorder, while other patients, including adult males and most affected female carriers, experience a chronic progressive myelopathy. Adrenocortical failure is observed in almost all male patients, with age of onset varying sometimes being the first diagnostic finding. The gene underlying this spectrum of disease encodes an ATP-binding cassette (ABC) transporter that localizes to peroxisomes and facilitates VLCFA transport. X-ALD is considered a single peroxisomal component defect and does not play a direct role in peroxisome assembly. Drosophila models of other peroxisomal genes have provided mechanistic insight into some of the neurodegenerative mechanisms with reduced lifespan, retinal degeneration, and VLCFA accumulation. Here, we perform a genetic analysis of the fly ABCD1 ortholog Abcd1 (CG2316). Knockdown or deficiency of Abcd1 leads to VLCFA accumulation, salivary gland defects, locomotor impairment and retinal lipid abnormalities. Interestingly, there is also evidence of reduced peroxisomal numbers. Flies overexpressing the human cDNA for ABCD1 display a wing crumpling phenotype characteristic of the pex2 loss-of-function. Surprisingly, overexpression of human ABCD1 appears to inhibit or overwhelm peroxisomal biogenesis to levels similar to null mutations in fly pex2, pex16 and pex3. Drosophila Abcd1 is therefore implicated in peroxisomal number, and overexpression of the human ABCD1 gene acts a potent inhibitor of peroxisomal biogenesis in flies.

Making Patterned Single Defects in MoS2 Thermally with the MoS2/Au Moiré Interface.

Normally, it is hard to regulate thermal defects precisely in their host lattice due to the stochastic nature of thermal activation. Here, we demonstrate a thermal annealing way to create patterned single sulfur vacancy (VS) defects in monolayer molybdenum disulfide (MoS2) with about 2 nm separations at subnanometer accuracy. Theoretically, we reveal that the S-Au interface coupling reduces the energy barriers in forming VS defects and that explains the overwhelming formation of interface VS defects. We also discover a phonon regulation mechanism by the moiré interface that effectively condenses the Γ-point out-of-plane acoustic phonons of monolayer MoS2 to its TOP moiré sites, which has been proposed to trigger moiré-patterned thermal VS formation. The high-throughput nanoscale patterned defects presented here may contribute to building scalable defect-based quantum systems.

Optical and electrical studies on the TS defect in 4H-SiC

Abstract When annealing a 4H silicon carbide (SiC) crystal, a sequence of optically active defect centers
occurs among which the TS center is a prominent example. Here, we present low-temperature photoluminescence
analyses on the single defect level. They reveal that the three occurring spectral
signatures TS1, TS2 and TS3 originate from one single defect. Their polarization dependences expose
three different crystallographic orientations in the basal plane, which relate to the projections of
the nearest neighbor directions. Accordingly, we find a three-fold level-splitting in ensemble studies,
when applying mechanical strain. This dependency is quantitatively calibrated. A complementary
electrical measurement, deep level transient spectroscopy, reveals a charge transition level of the TS
defect at 0.6 eV above the valence band. For a future identification, this accurate characterization
of its optical and electronic properties along with their response to mechanical strain is a milestone.

Analysis on the vibration signals of a novel double-disc crack rotor-bearing system with single defect in inner race

Previous studies have paid little attention to the dynamic modeling of multi-fault systems with both bearing defect and cracked rotor. In the current research, a double-disc rotor model with a breathing crack and fault bearing was established using the finite element method (FEM). The dual-impulse phenomenon associated with inner race defect was addressed as a time-varying external excitation. The effects of varying crack depths and inner race spall lengths were further investigated. The maximum error between simulation and experiment was found to be less than 5% for the dual-impulse time spacing. The calculated results indicate that the inner race defect causes a slight increase in the rotational frequency frotor and 2frotor, followed by a decrease in the 3frotor at low speeds, as observed using Fast Fourier Transform (FFT) and Short-Time Fourier Transform (STFT). The influence of changes in crack depth is greater than the bearing defect in the system, a finding that is also confirmed at 1/2 critical speed. The phenomenon of frequency modulation observed in the simulation was also verified experimentally. The ball passing frequency on inner raceway fBPFI, frotor and mixed frequency components can be used to distinguish whether there is inner race defect.

Thermoelectric properties of pristine and defective α-graphyne nanoribbons with vacancies present in different positions

In the present work, first-principle thermoelectric property investigations of pristine and defective α-graphyne nanoribbons (α-GYNRs) are conducted. Investigations have also been extended toward variation in temperature affecting the thermoelectric properties. Other objectives of the work presented are to investigate the thermoelectric properties at three temperatures, 300K, 500K, and 700K, of a single vacancy defect in a carbon atom removed from α-GYNRs. Pristine α-GYNRs is an intrinsic band gap semiconductor since defects occur naturally during synthesis, and the band gap significantly increases due to single vacancies and removal of carbon atoms at different positions. It results in a change of electrical conductivity Seebeck coefficient, and thermal conductivity. For some defective structures, with increasing temperature, the Seebeck coefficient increases compared with that of the pure structure and decreases. Also, the total thermal conductivity increases with increasing temperature. The obtained results show that the figure-of-merit value of defective α-GYNRs is much better than pristine α-GYNRs. In addition, ZT decreases in different structures by increasing temperature. Among all the considered structures, the Seebeck coefficient values and the ZT of some defective structures reach about 1.18 and 2.5 times that of the pristine structures at room temperature, respectively.