Distribution Of Structural Defects Research Articles

An Automated Analysis of Homocoupling Defects Using MALDI-MS and Open-Source Computer Software.

Conjugated organic polymers have substantial potential for multiple applications but their properties are strongly influenced by structural defects such as homocoupling of monomer units and unexpected end-groups. Detecting and/or quantifying these defects requires complex experimental techniques, which hinder the optimization of synthesis protocols and fundamental studies on the influence of structural defects. Mass spectrometry offers a simple way to detect these defects but a manual analysis of many complex spectra is tedious and provides only approximate results. In this work, we develop a computational methodology for analyzing complex mass spectra of organic copolymers. Our method annotates spectra similarly to a human expert and provides quantitative information about the proportions of signal assigned to each ion. Our method is based on the open-source Masserstein algorithm, which we modify to handle large libraries of reference spectra required for annotating complex mass spectra of polymers. We develop a statistical methodology to analyze the quantitative annotations and compare the statistical distributions of structural defects in polymer chains between samples. We apply this methodology to analyze commercial and lab-made samples of a benchmark polymer and show that the samples differ both in the amount and in the types of structural defects.

Roadmap toward Controlled Ion Beam‐Induced Defects in 2D Materials

AbstractUnderstanding the nature, density, and distribution of structural defects is crucial for tailoring the properties of atomically thin two‐dimensional (2D) materials, which is paramount for advances in nanotechnology. Ion irradiation emerges as a promising technique for defect engineering of single‐atom‐thick materials, due to its high controllability, repeatability, and accuracy. The objective is to provide a comprehensive review elucidating the impact of various irradiation parameters, such as ion mass, energy, fluence, and incident angle, on defect formation in 2D materials. However, the presence of the substrate can significantly influence defect yield and the mechanism of formation due to backscattered ions and sputtered substrate atoms. Hence, a thorough comparison of ion beam‐induced defects in both freestanding (suspended) and supported (on a substrate) 2D materials, with a focus on substrate effects is conducted. Moreover, a detailed analysis of characterization techniques suitable for each scenario will be provided. This work not only contributes to advancing the current understanding of defect formation and evolution in 2D materials during ion beam irradiation but also offers insights into selecting specific parameters for this process to create desired defects in these materials. Consequently, it has the potential to facilitate the design of nanoscale devices with tailored functionality.

About the distribution of structural defects in sapphire

About the distribution of structural defects in sapphire

Development of Comprehensive Rating for the Evaluation of Sewer Pipelines

The Pipeline Assessment and Certification Program (PACP) was developed by the National Association of Sewer Service Companies, the industry-accepted protocol for condition rating sewer pipes in the US. The PACP method relies exclusively on visual inspections performed using closed-circuit television (CCTV), where certified operators observe existing structural and operation and maintenance (O&M) defects limitation of the PACP method is that it does not use pipe characteristics, depth, soil type, surface conditions, pipe criticality, and capacity, nor the distribution of structural defects or history of preventative maintenance to determine the condition rating of the sewer pipe segment. Therefore, this research addresses the limitations of the PACP with the development of a new wastewater pipe rating system known as the comprehensive rating (CR) system. The CR evaluation system is based on a commonly used decision-making approach known as the analytical hierarchy process (AHP) to analyze problems and issues. The new CR model incorporates pipe characteristics (age, corrosion, diameter, and shape), external characteristics (depth, soil type, traffic loading, waste type, seismic zone), and hydraulic characteristics (structural score, O&M score, and repair history). The results showed a below-average validity percentage because linear regression assumes a linear relationship between the input and output variables but the relationship between the response and the predictor is not linear.The CR methodology can be improved by increasing the number and variability of experts who evaluate the condition of existing sewer pipes, enhancing geospatial data for locational accuracy, and establishing evaluation standards for inspectors to minimize human error. More research is needed to determine a suitable nonlinear relation that can be used to model data from this new comprehensive rating system.

Fabrication of Sx/In2O3−x based microsphere for photoexcitation enhancing the NO2 gas detection properties

Development research as a NO2 gas sensor has attracted extensive attention recently. However, how to improve the electrical conductivity of materials, adjust the band structure of materials through photoexcitation and improve the carrier lifetime is still a challenge. In this work, an S-doped In2O3 structure (Sx/In2O3−x) was synthesized by enforcing the simple hydrothermal method. Doping directly controls the distribution of structural defects and oxygen vacancies in the material structure, and the response to NO2 increases by orders of magnitude under photoexcitation. Various structural characterization techniques examined the properties of the Sx/In2O3−x-based material. More specifically, its electro-optical properties and the impact of S doping on its energy band structure were thoroughly analyzed to investigate the origins of the enhanced responsivity.

Depth selective magnetic phase coexistence in FeRh thin films

We demonstrate the manipulation of magnetic phases in FeRh thin films through atomic displacements and the distribution of structural defects. Atomic scale disorder can be controlled via irradiation with light noble gas ions, producing depth-varying nanoscale phase configurations of distinct antiferromagnetic, ferromagnetic, and paramagnetic regions. Here, we perform a spatial characterization of the magnetic phases and the local magnetic environment around the Fe atoms, as well as the variation of the open-volumes around atomic sites. Thus, a direct correspondence between the existence of the three magnetic phases and lattice defects is revealed. By careful selection of the irradiating fluence, we show that it is possible to produce simple and thermally stable magnetic configurations, such as uniform magnetization or a bilayer phase structure. Furthermore, the thin film surface and interfaces are observed as the nucleation sites for the transitions between the phases. These results demonstrate a sensitive nanoscale manipulation of magnetic properties, shedding light on magnetic ordering in alloy lattices and broadening the scope for applications.

In situ topographical chemical and electrical imaging of carboxyl graphene oxide at the nanoscale

Visualising the distribution of structural defects and functional groups present on the surface of two-dimensional (2D) materials such as graphene oxide challenges the sensitivity and spatial resolution of the most advanced analytical techniques. Here we demonstrate mapping of functional groups on a carboxyl-modified graphene oxide (GO–COOH) surface with a spatial resolution of ≈10 nm using tip-enhanced Raman spectroscopy (TERS). Furthermore, we extend the capability of TERS by measuring local electronic properties in situ, in addition to the surface topography and chemical composition. Our results reveal that the Fermi level at the GO–COOH surface decreases as the ID/IG ratio increases, correlating the local defect density with the Fermi level at nanometre length-scales. The in situ multi-parameter microscopy demonstrated in this work significantly improves the accuracy of nanoscale surface characterisation, eliminates measurement artefacts, and opens up the possibilities for characterising optoelectronic devices based on 2D materials under operational conditions.

Elucidation of Iron Gettering Mechanisms in Boron-Implanted Silicon Solar Cells

To facilitate cost-effective manufacturing of boron-implanted silicon solar cells as an alternative to BBr3 diffusion, we performed a quantitative test of the gettering induced by solar-typical boron-implants with the potential for low saturation current density emitters (<50 fA/cm2). We show that depending on the contamination level and the gettering anneal chosen, such boron-implanted emitters can induce more than a 99.9% reduction in bulk iron point defect concentration. The iron point defect results as well as synchrotron-based nano-X-ray-fluorescence investigations of iron precipitates formed in the implanted layer imply that, with the chosen experimental parameters, iron precipitation is the dominant gettering mechanism, with segregation-based gettering playing a smaller role. We reproduce the measured iron point defect and precipitate distributions via kinetics modeling. First, we simulate the structural defect distribution created by the implantation process, and then we model these structural defects as heterogeneous precipitation sites for iron. Unlike previous theoretical work on gettering via boron- or phosphorus-implantation, our model is free of adjustable simulation parameters. The close agreement between the model and experimental results indicates that the model successfully captures the necessary physics to describe the iron gettering mechanisms operating in boron-implanted silicon. This modeling capability allows high-performance, cost-effective implanted silicon solar cells to be designed.

Spatial distribution of structural defects in Cz-seeded directionally solidified silicon ingots: An etch pit study

The PV properties of wafers processed from Cz-seeded directionally solidified silicon ingots suffer from variable structural defects. In this study, we draw an overview on the types of structural defects encountered in the specific case of full 〈1 0 0〉 oriented growth. We found micro twins, background dislocations, and subgrains boundaries. We discuss the possible links between thermomechanical stresses and growth processes with spatial evolution of both background dislocation densities and subgrain boundaries length.

TEM Study of the microstructure of melt grown FeGe2 single crystals

The results of transmission electron microscopy and metallographic investigation of the microstructure of FeGe2 single crystals are reported. The main defects revealed are edge dislocations, dislocation loops, and stacking faults located predominantly in close-packed crystallographic planes. The spatial distribution of structural defects is shown to correlate with the specific features of the growth technology. The dislocation density in the samples studied is about 104 cm–2 and is almost constant in a wide pulling-rate range. Small amounts of doping elements (Co, Al, Sn) do not significantly change the microstructure, and thus high quality crystals can be obtained after corresponding correction of the growth parameters.

Bulk growth of organic 4-hydroxy l-proline (HLP) single crystals grown by conventional slow evaporation and Sankaranarayanan–Ramasamy (SR) method

Organic single crystals of 4-hydroxy l-proline (HLP) were grown by conventional slow evaporation and Sankaranarayanan–Ramasamy (SR) method in an aqueous medium. With a vision to improve the crystal quality, SR method was adopted and optically transparent HLP single crystal, (110) directed, with the size of 80 mm length and 15 mm diameter was grown. The crystalline structure of the grown crystal was analyzed by single crystal X-ray diffraction (SXRD) analysis. The conventional and SR method grown HLP crystals were characterized and the results were compared by UV–Vis–NIR, photoluminescence, chemical etching, Vickers microhardness, dielectric permittivity, dielectric loss, photoconductivity, photoacoustic, laser damage threshold (LDT) and second harmonic generation (SHG) measurements. The thermal property of the grown crystal was carried out by thermogravimetric (TG) and differential thermal analysis (DTA). The SHG efficiency of HLP crystal was determined using Kurtz–Perry powder technique. The comparative optical transmittance study clearly indicates that the transmission of SR method grown HLP crystal is 10% higher and quite good in the entire visible and near infrared region which suggest its suitability for optical device applications. The distribution of structural defects and the etch pit density (EPD) of the grown crystals were determined by chemical etching analysis. The Vickers microhardness measurement reveals that the hardness of SR method grown HLP crystal is higher compared to conventional method grown crystal. The dielectrics, photoconductivity, photoacoustic and laser damage threshold studies clearly indicate that the crystal grown by SR method possesses good quality compared to conventional method grown crystal.

Vibration analysis of defective graphene sheets using nonlocal elasticity theory

Many papers have studied the free vibration of graphene sheets. However, all this papers assumed their atomic structure free of any defects. Nonetheless, they actually contain some defects including single vacancy, double vacancy and Stone-Wales defects. This paper, therefore, investigates the free vibration of defective graphene sheets, rather than pristine graphene sheets, via nonlocal elasticity theory. Governing equations are derived using nonlocal elasticity and the first-order shear deformation theory (FSDT). The influence of structural defects on the vibration of graphene sheets is considered by applying the mechanical properties of defective graphene sheets. Afterwards, these equations solved using generalized differential quadrature method (GDQ). The small-scale effect is applied in the governing equations of motion by nonlocal parameter. The effects of different defect types are inspected for graphene sheets with clamped or simply-supported boundary conditions on all sides. It is shown that the natural frequencies of graphene sheets decrease by introducing defects to the atomic structure. Furthermore, it is found that the number of missing atoms, shapes and distributions of structural defects play a significant role in the vibrational behavior of graphene. The effect of vacancy defect reconstruction is also discussed in this paper.

Evolution of Microstructural Disorder in Annealed Bismuth Telluride Nanowires

Controlling the distribution of structural defects in nanostructures is important since such defects can strongly affect critical properties, including thermal and electronic transport. However, characterizing the defect arrangements in individual nanostructures is difficult because of the small length scales involved. Here, we investigate the evolution of microstructural disorder with annealing in electrochemically deposited Bi2Te3 nanowires, which are of interest for thermoelectrics. We combine Convergent Beam Electron Diffraction (CBED) and Scanning Transmission Electron Microscopy (STEM) to provide the necessary spatial and orientational resolution. We find that despite their large initial grain sizes and strong crystallographic texturing, the as-deposited nanowires still exhibit significant intragranular orientational disorder. Annealing drives both grain growth and a significant reduction in the intragranular disorder. The results are discussed in the context of the existing understanding of the initial microstructure of electrodeposited materials and the understanding of annealing microstructures in both electrochemically deposited and bulk-deformed materials. This analysis highlights the importance of assessing both the grain size and intragranular disorder in understanding the microstructural evolution of individual nanostructures.

Influence of defect distribution on the reducibility of CeO2−x nanoparticles

Ceria nanoparticles (NPs) are fundamental in heterogeneous catalysis because of their ability to store or release oxygen depending on the ambient conditions. Their oxygen storage capacity is strictly related to the exposed planes, crystallinity, density and distribution of defects. In this work a study of ceria NPs produced with a ligand-free, physical synthesis method is presented. The NP films were grown by a magnetron sputtering based gas aggregation source and studied by high resolution- and scanning-transmission electron microscopy and x-ray photoelectron spectroscopy. In particular, the influence of the oxidation procedure on the NP reducibility has been investigated. The different reducibility has been correlated to the exposed planes, crystallinity and density and distribution of structural defects. The results obtained in this work represent a basis to obtain cerium oxide NP with desired oxygen transport properties.

The Influence of Heat Treatment on the Magnetization Process (within Strong Magnetic Fields) for the Alloy: Fe61Co10Y8Cu1B20

Abstract Samples of Fe61Co10Y8Cu1B20 alloy were investigated in the ‘approach to ferromagnetic saturation’ region by using the Kronmüller method. The amorphous material was obtained by radially cooling the molten alloy under a protective atmosphere of inert gas. Following this manufacturing process, static magnetic hysteresis loops were measured for samples, before and after a controlled isothermal annealing process, using a LakeShore vibrating magnetometer (VSM). From analysis of the primary magnetization curves, the distribution of structural defects and the average exchange distance for these defects were determined.

Correlation of Lifetime Mapping of 4H-SiC Epilayers with Structural Defects Using Synchrotron X-Ray Topography

Lifetime maps for two 4H-SiC epi-wafers (samples 1 and 2) were recorded using microwave photoconductive decay (μPCD) measurements and correlated with the type and distribution of structural defects mapped by synchrotron X-ray topography (white beam and monochromatic). Sample 1 showed lower lifetime inside one of its higher doped facet regions and along its edges. The low lifetime in the facet region was associated with the presence of a high density of multi-layered Shockley stacking faults (SFs) and low angle grain boundaries (LAGBs). These stacking faults are likely double Shockley stacking faults (DSSFs) and probably nucleated from scratches present on the substrate surface and LAGBs present in that region, propagating during epilayer growth. In contrast, sample 2 showed a reduced carrier lifetime in the middle region associated with a network of interfacial dislocations (IDs) and half loop arrays (HLAs) originating from 3C inclusions that are generated during epilayer growth. Along the edges of both samples, overlapping triangular defects, microcracks and BPD loops lowered lifetime.

Harmonic model of graphene based on a tight binding interatomic potential

Like in many other materials, the presence of topological defects in graphene has been demonstrated to modify its behavior, thus enhancing features aimed at several technological applications, more specifically, its electronic and transport properties. In particular, pristine defect-free graphene has been shown to be of limited use for semiconductor-based electronics, whereas the presence of individual or cluster defect rings along grain boundaries hinders electron transport and introduce a transport gap, unveiling the possibility of novel electronic device applications based on the structural engineering of graphene-based materials. In this work, we present an atomic bondwise force-constant model from the tight binding potential by Xu et al. (1992), that accounts for the electron-mechanical coupling effects in graphene. First we verify that this computational scheme is capable of accurately predicting the defect energies and core structures of dislocation dipoles based on the theory of discrete dislocations of Ariza and Ortiz (2005). In order to demonstrate our ability to characterize the effect of patterned distributions of structural defects on the electronic structure of graphene, we present the electronic band structures and density of states curves of several defective graphene sheets.

Birth prevalence of selected external structural birth defects at four hospitals in Dar es Salaam, Tanzania, 2011–2012

Background94% of all birth defects (BD) and 95% of deaths due to the BD occur in low and middle income countries, many of which are preventable. In Tanzania, there is currently a paucity of BD data necessary to develop data informed prevention activities.MethodsA cross-sectional analysis was conducted of deliveries identified with BD in the labor ward registers at four Dar es Salaam hospitals between October, 2011 and February, 2012. The birth prevalence of structural BD, case fatality proportion, and the distribution of structural defects associated deaths within total deaths were calculated.ResultsA total of 28 217 resident births were encountered during the study period. Overall birth prevalence of selected defects was 28.3/10 000 live births. Neural tube defects and indeterminate sex were the most and least common defects at birth (9.9 and 1.1/10 000 live births, respectively). Among stillbirths (66.7%) and deaths that occurred within less than 5 days of an affected live birth (18.5%), neural tube defects were the most frequently associated structural defect.ConclusionStructural BD is common and contributes to perinatal mortality in Dar es Salaam. More than half of perinatal deaths encountered among the studied selected external structural BD are associated with neural tube defects, a birth defect with well–established evidence based prevention interventions. By establishing a population–based BD surveillance program, Tanzania would have the information about neural tube defects and other major structural BD needed to develop and monitor prevention activities.

Residual Defect Density in Random Disks Deposits.

We investigate the residual distribution of structural defects in very tall packings of disks deposited randomly in large channels. By performing simulations involving the sedimentation of up to 50 × 109 particles we find all deposits to consistently show a non-zero residual density of defects obeying a characteristic power-law as a function of the channel width. This remarkable finding corrects the widespread belief that the density of defects should vanish algebraically with growing height. A non-zero residual density of defects implies a type of long-range spatial order in the packing, as opposed to only local ordering. In addition, we find deposits of particles to involve considerably less randomness than generally presumed.

Building intuition of iron evolution during solar cell processing through analysis of different process models

An important aspect of Process Simulators for photovoltaics is prediction of defect evolution during device fabrication. Over the last twenty years, these tools have accelerated process optimization, and several Process Simulators for iron, a ubiquitous and deleterious impurity in silicon, have been developed. The diversity of these tools can make it difficult to build intuition about the physics governing iron behavior during processing. Thus, in one unified software environment and using self-consistent terminology, we combine and describe three of these Simulators. We vary structural defect distribution and iron precipitation equations to create eight distinct Models, which we then use to simulate different stages of processing. We find that the structural defect distribution influences the final interstitial iron concentration ([ $$\hbox {Fe}_i$$ ]) more strongly than the iron precipitation equations. We identify two regimes of iron behavior: (1) diffusivity-limited, in which iron evolution is kinetically limited and bulk [ $$\hbox {Fe}_i$$ ] predictions can vary by an order of magnitude or more, and (2) solubility-limited, in which iron evolution is near thermodynamic equilibrium and the Models yield similar results. This rigorous analysis provides new intuition that can inform Process Simulation, material, and process development, and it enables scientists and engineers to choose an appropriate level of Model complexity based on wafer type and quality, processing conditions, and available computation time.