Active Defects Research Articles

Light Induced Degradation Quantification by Monitoring the VOC Output of Silicon Solar Cell Using Low-Cost Real-Time Virtual Instrumentation

Silicon-based solar cells suffer from different types of light-induced efficiency losses (can cause up to 10% loss), known as light-induced degradation (LID). Impurities, such as boron, iron, and oxygen, are common at different concentrations in these solar cells. They form active recombination defects in boron-doped mono-crystalline (Cz-Si) and multi-crystalline (mc-Si) solar cells during illumination. For the solar industry, this will lead to serious financial loss, hence the importance of inspecting and controlling the LID level accurately. Seeking to minimize the human factor and the inaccuracy that comes with it, we have proposed in this research a low-cost virtual instrumentation solution to provide a new real-time instrumentation technique for solar cell characteristics such as open circuit voltage (VOC). The virtual data acquisition system (VDAS) design is based on a low-cost Arduino board associated with MATLAB/Simulink software. Moreover, this system can collect in real time the values of solar cell outputs under prolonged illumination and under different temperatures of the LID test. Further, kinetic modeling of the solar cell output VOC variation as a function of light soak duration; shows the predominance of one type metastable defect over the LID test of c-Si solar cells. Additionally, degradation mechanism in mc-Si solar cells involve more than one metastable defect and are more complexes due to the mc-Si substrate elaboration technique compared to c-Si substrate. Furthermore, the temperature dependence of the concentrations (NVoc) and the thermal activation energies of the defects have been extracted from the experimental VOC measurements obtained using the VDAS. Finally, the system minimizes the test period and errors for solar cell characterization compared to traditional approaches.

All‐Optical Thermometry with Infrared Emitting Defects in Diamond

AbstractDiamond color centers (optically active defects) can be used for all‐optical thermometry for non‐invasive and localized temperature measurements. The visible to near‐infrared photoluminescence of these defects is greatly attenuated in optical fibres and biological samples and therefore limits their use. A color center in Si‐doped diamond with emission coinciding with the O‐band and a major biological transparency window has recently been reported. It has a zero phonon line (ZPL) at 1221 nm and well‐resolved phonon side‐band features. In this work, a strong temperature dependence above 150 K is observed, allowing for accurate temperature measurements up to approximately 420 K. The temperature can be determined via spectral shifts or thermal broadening of the ZPL and through the intensity ratio between the ZPL and the phonon side‐band to a maximum temperature resolution of 0.57 K/. Thermometry using these micro‐diamonds is demonstrated for both electronic and biological applications highlighting their versatility. The potential for further enhancements in sensitivity is discussed.

Boosting H2S gas sensing performance of metal oxide semiconductors at room-temperature by the electron-extracting effect of Pt nanocluster

Hydrogen sulfide (H2S) is not only a hazardous gas harmful to environment, but is also a marker molecule for periodontitis. In this study, a sensitive H2S sensing chip was developed based on Pt nanocluster (NC) decorated TiO2@ZnFe2O4 nanotube arrays for room temperature (RT) operation. Benefiting from the plentiful defects induced by PtNC and the selectivity of ZnFe2O4 towards H2S, high sensing response and excellent specificity were achieved by the resulting sensing chips. The abundant energetic active defects (Ov and Pt+δ species) were mainly responsible for triggering the sensing reactions of H2S in the absence of traditional thermal energy and UV irradiation. Based on the excellent electron transfer properties and the electron-extracting effect of PtNC, the resulting samples exhibited a remarkably high sensitivity for H2S with a low limit of detection of 0.43 ppb and a response value of 16.6 towards 10 ppm H2S gas. This sensing chip also displayed good selectivity, reproducibility (RSD < 3 %), and long-term storage stability (RSD < 4 %). The successful application of PtNC provides a novel way to improve the sensing performance of metal oxide semiconductor-based chemiresistor gas sensors at RT.

Monolayer Borophene Formation on Cu(111) Surface Triggered by Step Edge.

Borophene, a promising material with potential applications in electronics, energy storage, and sensors, is successfully grown as a monolayer on Ag(111), Cu(111), and Au(111) surfaces using molecular beam epitaxy. The growth of two-dimensional borophene on Ag(111) and Au(111) is proposed to occur via surface adsorption and boron segregation, respectively. However, the growth mode of borophene on Cu(111) remains unclear. To elucidate this, scanning tunneling microscopy in conjunction with theoretical calculations is used to study the phase transformation of boron nanostructures under post-annealing treatments. Results show that by elevating the substrate temperature, boron nanostructures undergo an evolution from amorphous boron to striped-phase borophene (η = 1/6) adhering to the Cu step edge, and finally to irregularly shaped β-type borophene (η = 5/36) either on the substrate surface or embedded in the topmost Cu layer. dI/dV spectra recorded near the borophene/Cu lateral interfaces indicate that the striped-phase borophene is a metastable phase, requiring more buckling and electron transfer to stabilize the crystal structure. These findings offer not only an in-depth comprehension of the β-type borophene formation on Cu(111), but also hold potential for enabling borophene synthesis on weakly-binding semiconducting or insulating substrates with 1D active defects.

Oxygen-vacancy defect in 4H-SiC as a near-infrared emitter: An ab initio study

Optically active spin defects in semiconductors can serve as spin-to-photon interfaces, key components in quantum technologies. Silicon carbide (SiC) is a promising host of spin defects thanks to its wide bandgap and well-established crystal growth and device technologies. In this study, we investigated the oxygen-vacancy complexes as potential spin defects in SiC by means of ab initio calculations. We found that the OCVSi defect has a substantially low formation energy compared with its counterpart, OSiVC, regardless of the Fermi level position. The OCVSi defect is stable in its neutral charge state with a high-spin ground state (S = 1) within a wide energy range near the midgap energy. The zero-phonon line (ZPL) of the OCVSi0 defect lies in the near-infrared regime, 1.11–1.24 eV (1004–1117 nm). The radiative lifetime for the ZPL transition of the defect in kk configuration is fairly short (12.5 ns). Furthermore, the estimated Debye–Waller factor for the optical transition is 13.4%, indicating a large weight of ZPL in the photoluminescence spectrum. All together, we conclude that the OCVSi0 defect possesses desirable spin and optical properties and thus is potentially attractive as a quantum bit.

Multiple reaction pathway on alkaline earth imide supported catalysts for efficient ammonia synthesis

The tunability of reaction pathways is required for exploring efficient and low cost catalysts for ammonia synthesis. There is an obstacle by the limitations arising from scaling relation for this purpose. Here, we demonstrate that the alkali earth imides (AeNH) combined with transition metal (TM = Fe, Co and Ni) catalysts can overcome this difficulty by utilizing functionalities arising from concerted role of active defects on the support surface and loaded transition metals. These catalysts enable ammonia production through multiple reaction pathways. The reaction rate of Co/SrNH is as high as 1686.7 mmol·gCo−1·h−1 and the TOFs reaches above 500 h−1 at 400 °C and 0.9 MPa, outperforming other reported Co-based catalysts as well as the benchmark Cs-Ru/MgO catalyst and industrial wüstite-based Fe catalyst under the same reaction conditions. Experimental and theoretical results show that the synergistic effect of nitrogen affinity of 3d TMs and in-situ formed NH2− vacancy of alkali earth imides regulate the reaction pathways of the ammonia production, resulting in distinct catalytic performance different from 3d TMs. It was thus demonstrated that the appropriate combination of metal and support is essential for controlling the reaction pathway and realizing highly active and low cost catalysts for ammonia synthesis.

Microscopic defect dynamics during a brittle-to-ductile transition

Deformation of all materials necessitates the collective propagation of various microscopic defects. On Earth, fracturing gives way to crystal-plastic deformation with increasing depth resulting in a "brittle-to-ductile" transition (BDT) region that is key for estimating the integrated strength of tectonic plates, constraining the earthquake cycle, and utilizing deep geothermal resources. Here, we show that the crossing of a BDT in marble during deformation experiments in the laboratory is accompanied by systematic increase in the frequency of acoustic emissions suggesting a profound change in the mean size and propagation velocity of the active defects. We further identify dominant classes of emitted waveforms using unsupervised learning methods and show that their relative activity systematically changes as the rocks cross the brittle-ductile transition. As pressure increases, long-period signals are suppressed and short-period signals become dominant. At higher pressures, signals frequently come in avalanche-like patterns. We propose that these classes of waveforms correlate with individual dominant defect types. Complex mixed-mode events indicate that interactions between the defects are common over the whole pressure range, in agreement with postmortem microstructural observations. Our measurements provide unique, real-time data of microscale dynamics over a broad range of pressures (10 to 200 MPa) and can inform micromechanical models for semi-brittle deformation.

Influence of porous support structure and the possible presence of active layer defects on FO membrane behaviour

In forward osmosis, defects on the selective active layer and changes in the porous structure of the support layer can be detrimental factors affecting the membrane performance. This study focuses on the impacts of (i) the possible presence of defects and (ii) the changes in pore structures on the water flux and membrane selectivity via computational fluid dynamics analyses. Results suggest that diffusion of the draw solute through the support layer, i.e. internal concentration polarization, can be strongly enhanced or reduced by widening or narrowing the shape of the pore, respectively, while no significant effect on water permeation can be associated with the change in draw solution cross-flow velocity or in the loss of draw solute during filtration. Interestingly, defects within the active layer may affect the water flux exponentially as function of the defect size, suggesting the presence of a threshold below which the convective passage of contaminated water flux through the defect is not affecting the membrane productivity. Moreover, the presence of defects may not be a detrimental factor for membrane operating with high nominal rejection (>90%) and low percentage of defected area (<1%).

Modification of Diamond Surface by Femtosecond Laser Pulses

The basic mechanisms of laser interaction with synthetic diamond are reviewed. The characteristics of the main regimes of diamond surface etching are considered. In addition to the well-known graphitization and ablation processes, nanoablation and accumulative graphitization, which have attracted relatively recent attention, are described in detail. The focus is on femtosecond (fs) laser exposure, which allows for the formation of a dense cold electron–hole plasma in the focal zone and minimal overheating in the surrounding area. This potentially opens the way to the development of unique laser-based technologies that combine physical and chemical processes for precise surface treatment and functionalization. The physical limitations that determine how precisely the diamond surface can be treated by short-pulsed laser radiation and possible ways to overcome them with the ultimate goal of removing ultrathin layers of the material are discussed. Special attention is paid to the novel possibility of inducing the local formation of point active defects—nitrogen vacancy (NV) complexes in the laser-irradiated zone. Such defects have been at the forefront of solid-state physics for the past thirty years due to continuous attempts to exploit their unique properties in quantum optics, quantum computing, magnetometry, probing, and other fields. Both regimes of NV center formation with and without graphitization of the diamond lattice are considered. Thus, it is shown that intense pulsed laser irradiation is a perfect tool for the processing of synthetic diamonds at the micro-, nano-, and even at the atomic level, which can be well controlled and managed.

Introduction Rates of Electrically Active Radiation Defects in Proton Irradiated n-Type and p-Type Si Monocrystals

Introduction Rates of Electrically Active Radiation Defects in Proton Irradiated n-Type and p-Type Si Monocrystals

Optically Active Spin Defects in Few-Layer Thick Hexagonal Boron Nitride.

Optically active spin defects in hexagonal boron nitride (hBN) are promising quantum systems for the design of two-dimensional quantum sensing units offering optimal proximity to the sample being probed. In this Letter, we first demonstrate that the electron spin resonance frequencies of boron vacancy centers (V_{B}^{-}) can be detected optically in the limit of few-atomic-layer thick hBN flakes despite the nanoscale proximity of the crystal surface that often leads to a degradation of the stability of solid-state spin defects. We then analyze the variations of the electronic spin properties of V_{B}^{-} centers with the hBN thickness with a focus on (i)the zero-field splitting parameters, (ii)the optically induced spin polarization rate and (iii)the longitudinal spin relaxation time. This Letter provides important insights into the properties of V_{B}^{-} centers embedded in ultrathin hBN flakes, which are valuable for future developments of foil-based quantum sensing technologies.

Quality of medicines in Sri Lanka: a retrospective review of safety alerts

BackgroundMany medicine quality problems are detected after they arrive at health facilities. Thus, critically defective medicines that may pose health risks to patients need to be withheld or recalled.AimsTo investigate the withheld and recalled medicines in relation to the types of defects, their total numbers, therapeutic categories, pharmaceutical dosage forms, and country of manufacturer during the study period.MethodsA retrospective review was performed on withheld and recalled medicines published on the publicly available National Medicines Regulatory Authority (NMRA) official website in Sri Lanka between June 2018 and August 2021. Details on substandard medicines (SM) were extracted and documented. Each record of SM was individually reviewed to determine the type of defect, subsequent action taken by NMRA, therapeutic category, pharmaceutical dosage form, and country of manufacturer.ResultsA total of 163 defects were identified in 143 defective medicines, among which the most common types of defects were contamination (n = 59, 36.2%), stability defects (n = 41, 25.2%), packaging and labelling defects (n = 27, 16.6%) and active pharmaceutical ingredient defects (n = 26, 15.9%). Out of 143 total defective medicines identified, anti-infectives accounted for 41.9%, while parenteral preparations (44.0%) were found to be frequently defective. Nearly 70% of the recalled and withheld medicines were of Indian origin, and some manufacturers were identified to be repeatedly involved.ConclusionsThis study revealed that contamination was the most frequent cause of defective medicines, while parenteral preparations and anti-infectives were the most susceptible pharmaceutical dosage form and therapeutic category found to be substandard, respectively. In addition, the findings show that some manufacturers were accountable for repetitive withholdings and recalls, which reflects the ignorance of quality control measures and weak regulatory inspections as a violation of Good Manufacturing Practice (GMP).

Effect of internal energy depletion on active nematic texture and dynamics

ABSTRACTActive nematics represent a relatively new class of materials with liquid crystalline properties that rely on an energy source to maintain their structure and dynamics. In this paper, we focus on the well-known microtubule-kinesin-based active nematic, powered by chemical energy as ATP (Adenosine triphosphate), and report on how ATP depletion impacts active nematic defect dynamics and texture. Using fluorescence microscope video imaging, we measure the time averaged mean defect separations and root mean square velocities of the active flows as a function of time. We also characterise textural changes and the growth of void space in the network after ATP depletion using an image binarization technique.

Control on the density and optical properties of color centers at SiO2/SiC interfaces by oxidation and annealing

Color centers in solids can serve as single photon emitters (SPEs) those are important in many quantum applications. Silicon carbide (SiC) is a promising host for color centers because of its well-established crystal growth and device technologies. Although color centers with extremely high brightness were found at the silicon dioxide (SiO2)/SiC interface, controlling their density and optical properties remains a challenge. In this study, we demonstrate control over the color centers at the SiO2/SiC interface by designing the oxidation and annealing conditions. We report that post-oxidation CO2 annealing has the ability to reduce the color centers at the interface and form well-isolated SPEs with bright emission. We also discuss the correlation between the color centers and electrically active defects.

Topological edge state assisted dynamically tunable microwave propagations in photonic crystals

Topological photonics has emerged as a cutting-edge and intriguing field that permits electromagnetic waves to transmit with minimal losses even when they come in contact with sharp turns or imperfections or defects. In this study, we validate a strategy to realize dynamically amplitude tunable light propagation in a topological waveguide based on a three-dimensional printed valley Hall photonic crystal structure operating in the microwave frequency region. Here, tunable light propagation is facilitated by inserting an active defect in the form of a semiconductor (silicon) material slab across the domain boundary of the topological waveguide. In this configuration, dynamic variation of transmission amplitude is realized via photoexcitation of the semiconductor defect using an external laser of wavelength, nm. This results in active amplitude tunability of dB in topological wave propagation under a photoexcitation of 100 mW. Our demonstrated route can lead to the design of dynamically controlled topological photonic devices such as optical modulators, switches, optical buffers, etc which are important for the development of 6G communication systems.

(Invited) Nanoscale Mapping of Electrochemical and Photoelectrochemical Processes on 2D Layered Materials by SECM

Electrocatalytic and photo(electro)catalytic activities of 2D materials are highly heterogeneous with different active sites, e.g., structural defects and facet edges, contributing to the overall current. Scanning electrochemical microscopy (SECM) and related techniques have been extensively used for localized measurements of electrocatalytic activity; however, the progress is hindered by the difficulty in pinpointing the active sites, particularly when their size is on the atomic scale. We have recently reported the use of SECM for nanoscale imaging of electrocatalytic reactions at 2D materials and photoelectrochemical processes at semiconductor surfaces. In this paper, we present new approaches to surface reactivity mapping, including electrochemical and photoelectrochemical tunneling experiments at monolayers and nm-thick exfoliated flakes of MoS2.

Development of a Low-Shrinkage-Lightweight Engineered Cementitious Composite Based on Heavily Doped Zeolites

In recent years, there has been a growing utilization of lightweight engineered cementitious composites (LECC) for the reinforcement and restoration of contemporary building structures. This study focuses on the incorporation of zeolite, serving as an internal reservoir for moisture maintenance, and examines its impact on various performance indicators, including apparent density, compressive strength, tensile strength, and autogenous shrinkage. Additionally, the influence of zeolite on the tensile and ductile properties of LECC is elucidated with the aid of scanning electron microscopy (SEM). The findings reveal that the addition of zeolite enables the preservation of excellent mechanical properties of LECC while further reducing its density. Notably, the introduction of a substantial amount of zeolite leads to a decrease in matrix density, average crack width, and ultimate tensile strain. The ultimate tensile strain exceeds 8% to reach 8.1%, while the decrease in compressive and tensile strengths is marginal. Zeolite’s internal curing capability facilitates the complete hydration of unhydrated cement, concurrently alleviating the autogenous shrinkage of LECC. Consequently, the durability and reliability of the material are enhanced. The ability of zeolite, with its porous framework structure, to significantly improve the ultimate tensile strain of the matrix can be attributed to the amplified occurrence of active defects and a shift in the pull-out mode of PE fibers from “pull-out” to “pull-through”. This study presents a promising alternative material in the field of engineering, holding potential for diverse building and infrastructure projects, as it enhances their durability and reliability.

Neighborhood social deprivation and healthcare utilization, disability, and comorbidities among young adults with congenital heart defects: Congenital heart survey to recognize outcomes, needs, and well-being 2016-2019.

Research on the association between neighborhood social deprivation and health among adults with congenital heart defects (CHD) is sparse. We evaluated the associations between neighborhood social deprivation and health care utilization, disability, and comorbidities using the population-based 2016-2019 Congenital Heart Survey To RecognizeOutcomes, Needs, and well-beinG (CH STRONG) of young adults. Participants were identified from active birth defect surveillance systems in three U.S. sites and born with CHD between 1980 and 1997. We linked census tract-level 2017 American Community Survey information on median household income, percent of ≥25-year-old with greater than a high school degree, percent of ≥16-year-olds who are unemployed, and percent of families with children <18 years old living in poverty to survey data and used these variables to calculate a summary neighborhood social deprivation z-score, divided into tertiles. Adjusted prevalence ratios (aPR) and 95% confidence intervals (CI) derived from a log-linear regression model with a Poisson distribution estimated the association between tertile of neighborhood social deprivation and healthcare utilization in previous year (no encounters, 1 and ≥2 emergency room [ER] visits, and hospital admission), ≥1 disability, and ≥1 comorbidities. We accounted for age, place of birth, sex at birth, presence of chromosomal anomalies, and CHD severity in all models, and, additionally educational attainment and work status in all models except disability. Of the 1435 adults with CHD, 43.8% were 19-24 years old, 54.4% were female, 69.8% were non-Hispanic White, and 33.7% had a severe CHD. Compared to the least deprived tertile, respondents in the most deprived tertile were more likely to have no healthcare visit (aPR: 1.5 [95% CI: 1.1, 2.1]), ≥2 ER visits (1.6 [1.1, 2.3]), or hospitalization (1.6 [1.1, 2.3]) in the previous 12 months, a disability (1.2 [1.0, 1.5]), and ≥1 cardiac comorbidities (1.8 [1.2, 2.7]). Neighborhood social deprivation may be a useful metric to identify patients needing additional resources and referrals.

Electron-transfer based selective oxidation of organic pollutants via N-doped biochar activated peroxydisulfate: Important role of oxidation potential

For persulfate-based advanced oxidation process, the non-radical pathway is an important route due to the selective oxidation of pollutants and its strong tolerance to complex water bodies. However, the selective oxidation mechanism of organic pollutants needs further elaboration. Herein, we demonstrate a facile hydrothermal pretreatment and high-temperature carbonization route to synthesize the nitrogen-doped porous biochar (NHBC-1). Owing to the well-developed hierarchical porous structure, the created internal active defects, and tailored nitrogen dopants, the NHBC-1 catalyst exhibited excellent catalytic activity for peroxydisulfate (PDS) activation. The results show that pyridinic N facilitated the adsorption of PDS on NHBC-1 to form the highly active NHBC-PDS* complex. Meanwhile, graphitic N and the defective structures promoted the electron-transfer process, thus allowing the efficient catalytic performance of the NHBC/PDS system for phenol oxidation via an electron-transfer dominated pathway. In addition, the system exhibited versatile applicability for the remediation of various organic pollutants in different actual water matrices with wide pH adaptability and satisfactory mineralization efficiency. More importantly, the selective oxidation mechanism of organic contaminants was revealed. Specifically, only the pollutant with oxidation potential lower than that of the NHBC-PDS* complex (0.91 V) can be effectively eliminated. This study not only provides a facile route for the rational designing of a cost-affordable biochar catalyst for PDS activation, but also offers valuable insights into the understanding of selective oxidation of organic contaminants via an electron-transfer dominated pathway.

Over- and Undercoordinated Atoms as a Source of Electron and Hole Traps in Amorphous Silicon Nitride (a-Si3N4).

Silicon nitride films are widely used as the charge storage layer of charge trap flash (CTF) devices due to their high charge trap densities. The nature of the charge trapping sites in these materials responsible for the memory effect in CTF devices is still unclear. Most prominently, the Si dangling bond or K-center has been identified as an amphoteric trap center. Nevertheless, experiments have shown that these dangling bonds only make up a small portion of the total density of electrical active defects, motivating the search for other charge trapping sites. Here, we use a machine-learned force field to create model structures of amorphous Si3N4 by simulating a melt-and-quench procedure with a molecular dynamics algorithm. Subsequently, we employ density functional theory in conjunction with a hybrid functional to investigate the structural properties and electronic states of our model structures. We show that electrons and holes can localize near over- and under-coordinated atoms, thereby introducing defect states in the band gap after structural relaxation. We analyze these trapping sites within a nonradiative multi-phonon model by calculating relaxation energies and thermodynamic charge transition levels. The resulting defect parameters are used to model the potential energy curves of the defect systems in different charge states and to extract the classical energy barrier for charge transfer. The high energy barriers for charge emission compared to the vanishing barriers for charge capture at the defect sites show that intrinsic electron traps can contribute to the memory effect in charge trap flash devices.