Types 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.

Thermal Battery Multi-Defects Detection and Discharge Performance Analysis Based on Computed Tomography Imaging

To address the typical structural defects that are prone to occur during the preparation and storage processes of thermal battery, experiments of battery image acquisition were designed based on X-ray computed tomography system. An improved Yolov5s network was employed to achieve high-precision automatic detection of typical defects. Through the discharge experiment of thermal battery, discharge performance curves of normal batteries and three defective batteries were constructed. The impact and mechanisms of different defects on the discharge performance were analyzed based on the voltage curve. By designing an automatic stitching scheme, the phenomenon of interlayer information overlap caused by the increase of cone angle in digital radiography images was suppressed. To address the issues of low image contrast and limited defect data in thermal battery imaging, the defect dataset was expanded using the designed image preprocessing steps and improving the contrast of the images. For subtle defects that are difficult to identify, the introduced multi-head self-attention mechanism in Transformer and the use of Focal Loss instead of cross-entropy loss function were employed to improve the recognition accuracy of subtle defects while ensuring the detection speed. The comparative experiment shows that the improved network model has higher recognition accuracy compared to Faster R-CNN, SSD, Cascade R-CNN, EfficientDet and the original Yolov5s network. The recognition accuracy of typical defects in thermal batteries can reach 98.7%.

Ultrasonic assessment of aging in lithium metal pouch cells

Lithium metal anodes are prone to non-uniform lithium plating that can lead to dendrite formation, internal short circuits, and catastrophic ignition. This type of structural defect is not captured by battery management systems, prompting the need to advance nondestructive evaluation (NDE) techniques that are suitable for periodic monitoring of the internal structure. An ultrasonic inspection technique is evaluated here as a means of identifying flaws and irregular lithium plating that can be a precursor to dendrite formation and, ultimately, battery failure.Lithium metal pouch cell batteries were aged through electrochemical cycling at a range of moderate constant-current charging and discharging rates. They were inspected intermittently using a tailored local ultrasonic resonance spectroscopy (LURS) approach that measures the local through-thickness resonances of the battery as an indicator of the underlying structure. LURS results showed clear structural resonances in cells in the range of 3–7 MHz, which shifted significantly to lower frequencies as batteries aged. In addition to point measurements, scanning LURS measurements were implemented to map resonance frequencies over the electrode surface. These resonance maps revealed spatial variations in structure that developed during aging and showed better contrast to structural variation than achieved using conventional amplitude-based c-scans of the specimens.NDE results from pouch cell measurements were compared to a destructive physical analysis of the electrode structures using scanning electron microscopy (SEM). The SEM results showed differences in the end-of-life lithium anode structure at different charge rates. The results of this study show the capability of LURS as a means for identifying changes in battery structures during aging and establish resonance trends that may be applied in future work for prognostic modeling of batteries in service.

The influence of spark plasma sintering on multiscale mechanical properties of nickel-based composite materials

The paper presents a comprehensive investigation of the influence of the main process parameters of spark plasma sintering on the mechanical and microstructural properties of nickel-silicon carbide composites at various scales. Microstructure analysis performed by scanning and transmission electron microscopy revealed a significant interfacial reaction between nickel and silicon carbide due to the decomposition of silicon carbide. The chemical interaction of the matrix and reinforcement results in the formation of a multicomponent interphase zone formed by silicides (Ni31Si12 or/and Ni3Si) and graphite precipitates. Furthermore, several types of structure defects were observed (mainly nano/micropores at the phase boundaries). These significantly influenced the mechanical response of nickel-silicon carbide composites at different levels. At the macroscopic scale, uniaxial tensile tests confirmed that applying a 1000 °C sintering temperature ensured that the manufactured composite was characterised by satisfactory tensile strength, however, with a considerable reduction of material elongation compared to pure nickel. Moreover, the fractography study allowed us to identify a significant difference in the damage mode for certain nickel-silicon carbide samples. Secondly, the interface of the nickel matrix and silicate interphase was tested by bending with microcantilevers to evaluate its deformation behaviour, strength, and fracture characteristics. It was confirmed that a diffusive kind of interface, such as Ni-NiSi, demonstrates unexpected bonding properties with a relatively large range of plastic deformation. Finally, the nanoindentation of three main components of the nickel-silicon carbide composite was executed to evaluate the evolution of nanohardness, Young's modulus, and elastic recovery due to the application of various spark plasma sintering conditions.

Comparing neutron and helium ion irradiation damage of REBa2Cu3O coated conductor using x-ray absorption spectroscopy

Understanding the effects of high energy neutron damage on REBa2Cu3O (REBCO) coated conductor is of vital importance for the design of the magnetic confinement systems for compact nuclear fusion power plants. However, neutron irradiation campaigns can only be carried out in a few facilities, and the experiments are very slow and expensive partly because the samples become radioactive. Ion irradiation provides an easily accessible alternative route to studying the effects of radiation on high temperature superconductors, which not only increases the volume of technical data that can be obtained but also enables more complex experiments such as in situ cryogenic irradiation. The question is, does ion damage offer a good proxy for neutrons? Here we use high energy resolution fluorescence detected x-ray absorption spectroscopy to probe the effects of fast neutron irradiation on the local environment around the copper ions in the REBCO layer of coated conductor tapes. We find that the spectral changes are similar to those induced by helium ion irradiation, suggesting that both projectiles produce the same types of structural defect in the REBCO lattice, although there is some evidence of an additional type of defect present in the sample heavily damaged by He+ ion irradiation. It is also shown that the linear degradation of superconducting transition temperature (T c ) of coated conductors with the calculated number of displacements per atom occurs at the same rate for neutrons and helium ions. Together these results provide new evidence suggesting that helium ions can emulate neutron point defect damage in REBCO high temperature superconductor reasonably well, increasing confidence that helium ions could be used as a useful proxy for neutrons in future experiments.

Influence of structural defects on charge density waves in 1T-TaS2

The influence of intrinsic defects of 1T-TaS2 on charge density waves (CDWs) is studied using scanning tunneling microscopy and spectroscopy (STM, STS), angle-resolved photoelectron spectroscopy (ARPES), and density functional theory (DFT). We identify several types of structural defects and find that most have a local character limited to a single CDW site, with a single exception which effectively behaves as a dopant, leading to band-bending and affecting multiple neighboring sites. While only one type of defect can be observed by STM topographic imaging, all defects are easily resolved in STS mapping. Our results indicate modulation of the Mott band gap commensurate with the CDW and breaking of the three-fold symmetry of electronic states. DFT calculations (with included Coulomb interactions) are used to investigate the electronic structure, focusing on both sulfur vacancy and oxygen-sulfur substitution. The sulfur vacancy system, characterized with a metallic behavior, is identified as the origin of one of the experimentally observed defects. Additionally, the effect of oxidation of 1T-TaS2 depends on the substitution site, leading to the heterogeneity of electronic properties.

Tuning the defects density in additively manufactured fcc aluminium alloy via modifying the cellular structure and post-processing deformation

In this study, using an L-PBF AlSi10Mg alloy with different microstructural properties, the typical structural defects caused by severe plastic deformation are investigated by scanning electron microscopy and high-resolution transmission electron microscopy. Microscopic characterization shows that the deformed L-PBF AlSi10Mg alloy exhibits a heterogeneous microstructure consisting of Al/Si interfaces and a high density of dislocations, stacking faults, and nanotwins. On the basis of experimental data, it is also shown that high stresses build up at the Al/Si interface due to incompatible deformation, enabling the activation of novel deformation modes that control the plastic deformation of the hard Si twin phase and amorphization in the solid state. The revealed synergy and novel deformation modes open a new horizon for the development of next-generation structural materials and provide insights into the atomically resolved structures of dislocations and GBs in nanostructured L-PBF alloys.

Sympetalous defects in metalorganic vapor phase epitaxy (MOVPE)-grown homoepitaxial β-Ga2O3 films

We report a new type of structural defect in β-Ga2O3 homoepitaxial thin films grown by metalorganic vapor phase epitaxy, which we have dubbed as “sympetalous defects.” These consist of a line defect (for example, a nanotube defect) in the underlying substrate combined with a multi-faceted inverted polycrystalline pyramid in the epitaxial film, which may also be decorated with twinned polycrystalline grains. In plan-view atomic force, scanning electron, or optical microscopies, the sympetalous defects appear similar in shape to polygonal etch pits observed for single crystals. Photoluminescence microscopy exposed spots of polarization-dependent luminescence at these defects, different from the single crystal films' luminescence. Furthermore, some of the defects exhibited circular dichroism in their luminescence that we correlated with partial helices formed within the pits by the arrangement of linearly dichroic polycrystalline grains. Finally, the density of sympetalous defects agrees with the etch pit densities of the substrates. Understanding and controlling these defects will be of importance as they modify the local properties of films, affect fabricated device yields, and influence characterization experiments.

Detecting, quantifying, and mapping urban trees' structural defects using infrared thermography: Implications for tree risk assessment and management

Urban trees are a fundamental and key component of urban green areas, however, they are subject to several stresses which can compromise their mechanical integrity through the development of defects such as wood decay. In this study, we evaluated the structural health state of trees in four urban parks in the city of Mytilene, Greece, using structural traits of the trees, their trunk surface temperature distribution as recorded using infrared thermography, and spatial statistics both at single tree and at park level. We developed thermal indices by analyzing data from 334 trees belonging to three main species (Robinia pseudoacacia, Morus alba and Melia azedarach). We estimated temperature spatial dependence across each tree trunk using Moran's I index, while statistically significant spatial clusters were assessed using local spatial autocorrelation statistics. Relationships between tree traits, thermal, and spatial indices were established using linear and logistic regression models. Finally, we used the Getis-Ord Gi* statistic for the identification of risky tree hotspots and we applied the kriging geostatistical procedure for mapping of such hotspots. Our results have shown that the thermal and spatial indices can sufficiently predict different types of structural defect, and to identify hotspots of risky trees and their spatial extent. This approach can successfully contribute to tree risk assessment for a more effective urban park management.

Effects of chiral index, vacancy defects and external electric field on the structures and electronic properties of DWSiNTs by SCC-DFTB calculations

As a new candidate material, silicon nanotubes (SiNTs) have been widely studied. However, various types of structural defects and external electric field are usually inescapability introduced in the experimental process of SiNTs synthesis. Structures, stability and electronic properties of the materials especially for double-walled silicon nanotubes (DWSiNTs) require to be considered. In this work, effects of vacancy defects and external electric field on properties of the geometrically structural optimization and electronic properties of DWSiNTs zigzag (3,0)@(7,0) and armchair (3,3)@(7,7) are studied via the self-consistent charge density functional tight binding (SCC-DFTB) method. The results of us show that the regular arrangement of the atoms, quantum molecular descriptors, distribution of charge, the degree of warping, stability, energy gap and Fermi energy levels intensely hinge on the chirality index of the tube and impacts of vacancy defects and electric field. Especially, the appearance of monovacancy and the change of vacancy density have the most significant effect on the band gap. For the pristine tubes, the charges transfer from the inside to the outside along the radial direction of the tube exhibiting an axisymmetric distribution. With the introduction of defects, the range of the charge transfer is broadened dramatically. The direction of charge transfer in the applied electric field is always opposite to the field direction. Our work may provide a new route to tune the electronic properties of DWSiNTs and opens a wider field of its application in nano-electronic devices.

Comparative evaluation of inspection techniques for decay detection in urban trees

A crucial problem associated with urban trees is the need ensure citizens’ safety. It requires the development and application of rapid and precise diagnostic techniques for detecting decay and other types of structural defects in trees to prevent falling due to strength failure or damage caused by internal decay. Significant effort has been devoted to developing robust non-destructive technologies, such as specialized sensors, capable of predicting the intrinsic properties of the wood of individual trees. In this study, the authors used four different devices with its sensors to measure decay: a microsecond timer, an electric resistivity tomograph, an acoustic tomograph and a resistograph. An inspection protocol combined stress wave, electrical resistance, and drilling resistance to detect internal defects on Mindi trees (Melia azedarach L.) located in the city of Reggio Calabria in Southern Italy. The percentages of the decayed wood areas, calculated by the different instruments, were compared to establish at which degree the use of simple and rapid instruments can guarantee reliability in detecting the extent of damaged woody tissues. This study’s experimental results indicate high correlations between the resistance drilling and the stress wave methods. These high correlations may provide the opportunity to replace the resistograph with the microsecond timer or the acoustic tomograph, both of which are less invasive tools for detecting defects in standing trees. Compared to the resistograph, the electrical resistivity tomograph proved to be the least sensitive instrument for detecting wood decay.

In situ high temperature spectroscopic study of liquid inclusions and hydroxyl groups in high purity natural quartz

High purity natural based quartz is used as raw material for production of crucibles for solar-grade silicon production. The crucible properties are strongly related to presence of water and hydroxyl groups in the raw material. In this work, in situ temperature-dependent diffuse reflectance infrared (DRIFT) and Raman spectroscopy in the spectral range of the OH stretching modes, 3000–4000 cm−1, were used to investigate water inclusions and hydroxyl groups at temperatures up to 800 °C. DRIFT shows that a substantial amount of liquid water was removed at 700 °C whereas new silanol groups characterised by stretching modes at about 3650 cm−1 were formed above 200 °C. A surface OH mode was also identified by multivariante curve resolution (MCR) of Raman maps. These surface OH groups were interpreted as the sign of formation of a hydrated layer at the surface of inclusions. It was not possible to detect water signals in other types of structural defect like cracks. Images were acquired in an in situ cell showing different stages of the rupture of an inclusion with a diameter of ≈8 μm between 400 and 500 °C. The in situ Raman spectrum of the inclusion water showed the typical liquid water bands at room temperature with a maximum moving to higher wavenumbers with increasing temperature. At 400 °C, the single peak at 3645 cm−1 indicated a situation close to the critical point, triggering rupture. The rupture of such large inclusions was thus identified as the dominating channel for the removal of liquid water inclusions. A small inclusion with a diameter ≈4 μm, however, was stable even at 800 °C. These small inclusions contain supercritical water, as evidenced by the sharp Raman peak at 3600 cm−1. Via the peak position, the internal pressure in this stable inclusion was estimated to be 90 MPa. Stability may be facilitated by the formation of a hydrated interfacial layer; the different reactivities of the inclusion fluid at different temperatures leads to different interfacial structures at different temperatures. The presented evidence suggests that inclusions with diameter in the range of few μm are the main source of remaining water and hydroxyl groups in thermally treated high purity quartz sand.

Time-Resolved Raman Scattering in Exfoliated and CVD Graphene Crystals

Phonon lifetimes are fundamental physical parameters playing a significant role in phonon transport and thermal conductivity of two-dimensional materials. We employed the time-resolved incoherent anti-Stokes Raman scattering (TRIARS) technique to capture the G phonon dynamics and to extract the G phonon lifetimes in supported exfoliated and polycrystalline chemical vapor deposited (CVD) graphene samples of various thickness. We have found that substrate reduces considerably the G phonon lifetime of exfoliated monolayer graphene while the corresponding lifetimes for bilayer and trilayer converge gradually close to that of graphite. The lifetimes of CVD monolayers are systematically lower than exfoliated ones mainly due to the presence of various types of structural defects. Besides, the electron–phonon coupling strength of graphite is determined to be 10.6 cm–1, in excellent agreement with theoretical predictions for graphene, justifying that the lifetimes of suspended graphene and graphite are similar.

Effect of electron-irradiation on layered quantum materials

Technological advancement towards the quantum era requires secure communication, quantum computation and ultra-sensitive sensing capabilities. Layered quantum materials (LQMs) have remarkable optoelectronic and quantum properties that can usher us into the quantum era. Electron microscopy is the tool of choice for measuring these LQMs at an atomic and nanometre scale. On the other hand, electron-irradiation of LQMs can modify various material properties, including the creation of structural defects. We review different types of structural defects, as well as electron elastic- and inelastic-scattering induced processes. Controlled modification of optoelectronic and quantum properties of LQMs using electron-irradiation, including creation of single-photon emitters is discussed. Protection of electron-irradiation induced damage of LQMs via encapsulation by other layered materials is encouraged. We finally give insights into challenges and opportunities, including creating novel structures using an electron beam.

Identification of Three Coexistent Defect Types in Hematite Photoanodes through Structure–Property Analysis

Structural defects present in hematite photoanodes are analyzed by correlating parameters derived from Raman spectra, band structure measurements and photoelectrochemical (PEC) oxygen evolution reaction performance. A series of photoanodes with varying quality of hematite are prepared by sintering akaganeite films with a systematically varied protocol. Data acquired through Raman microscopy, linear sweep voltammetry, and electrochemical impedance spectroscopy is parametrized and systematically compared to detect relationships amongst the data. Correlations between the structural information contained within the Raman spectra and PEC parameters enable the identification of three types of structural defects within the material. Each defect type is found to exert unique influence on PEC behavior and each became dominant under specific fabrication conditions. A straightforward approach to detecting defects in photoelectrodes and identifying their influence on photoelectrode properties and behavior is provided.

Research perspectives on the photocatalytic activity of titanium dioxide: Catalytic assessment methods in solution and solid-state in relation to particle surface activity

A range of prepared titania nanoparticles were characterised by Brunauer-Emmett-Teller (BET) surface area, X-ray Diffraction (XRD), CPS Disc Centrifuge, Transmission Electron Microscope (TEM), Scanning Electron Micrographs (SEM), Thermogravimetric Analysis (TGA) and Fourier Transform Infrared Measurements (DRIFTS). In addition, the activities of the different catalysts were determined via rapid assessment methodologies like Microwave Dielectric Spectroscopy (MDS), Hydroxyl content, Phosphorescence and Chemiluminescence Spectroscopy and Isopropanol Oxidation Test and the data related to actual weathering properties of the pigments doped in metallocene polyethylene under dry and humid conditions. Quantum size effects, which lead to high surface areas and blue shifts and diminish electron–hole recombination, are used to explain the high activities of the nanoparticle products. In situ FTIR data and OH content determination show the presence of high contents of hydroxyl groups and large amounts of adsorbed water on TiO2 nanoparticles. The Disc Centrifuge results and BET surface area combined with the XRD particle size results show that a careful distinction between the crystal and aggregate sizes must be made in order to properly interpret the activity of TiO2 pigments. Aggregation of TiO2 pigments affects not only the surface area offered by the TiO2 but also the type of interaction between the light and the TiO2. The treatment conditions used for the crystallization of the primary material (precursor) in order to prepare the nanoparticle pigments, not only influenced the anatase crystal size but also other anatase properties (such as the surface hydroxylation, adsorbed water, recombination rate, aggregation state and type of structural defects). Chemiluminescence of the titania particles is discussed in light of potential surface active peroxidic species.

Формирование и структура термомиграционных кремниевых каналов, легированных Ga

We have produced through-wafer vertical Si (Ga) p-channels by thermal migration of local gallium zones in c-Si (111) wafers. To achieve this, a method for the formation of local zone was proposed and implemented, which consists in filling linear grooves etched in a silicon wafer with fine-dispersed Ga powder. The grooves were 100 um wide and 30-50um deep. It was shown that a high yield of suitable zones occurs when the grain size of the powder is 5 um and the temperature is 290 K. The obtained Si (Ga) thermomigration p-channels were studied by X-ray methods of double-crystal rocking curves and projection topography. The characterization of structural perfection of Ga p-channels was performed by their comparison with the structural features of the Si (Al) thermomigration channels. Typical structural defects at the boundaries of both thermomigration channels were shown to be dislocation half-loops fixed by their ends at those boundaries. The concentrations of Al and Ga in the obtained channels were estimated as С(Al) ~ 1E19 и С(Ga) ~ 1.9 E19cm-3, the deformation e~(2–5)E-5 and tilt ~ 15–30 ʹʹ of crystal planes near the channel-matrix interface of the plate were determined.

SYNTHESIS OF TWO-DIMENSIONAL Fe-C ALLOY VIA MOLECULAR DYNAMICS SIMULATION

Formation of two-dimensional (2D) Fe-C alloy with square lattice structure from the liquid state is studied via molecular dynamics (MD) simulation. The researchers find that the crystallization of 2D Fe-C alloy exhibits a first-order-like phase transition. Evolution of structural and thermodynamic properties upon cooling from the melt of the model is investigated in details. Structural properties of the Fe50C50 model are investigated via the radial distribution function (RDF), coordination number, interatomic distance, and bond-angle distributions. The researchers find that Fe-Fe distance is 2.62Å, which is close to the value of DFT calculations and experiments. In addition, various types of structural defects are studied such as vacancies of different shapes and rings of several sizes clearly using the visualization’s software Visual Molecular Dynamics (VMD). Moreover, it can be proposed that the 2D Fe-C material would have many important applications in electronics and mechanic devices.

Growth defects in WC:H layers for tribological applications

Friction and wear resistance are important factors in almost all branches of industry, as they affect lifetime, power consumption and other properties of all mechanical tools and machines. Diamond-like carbon (DLC) and derived metal-carbon composite (WC:H) layers are known to substantially improve both of these factors and frequently find their use in tribological applications.One of the desired properties of the tribological layers is a smooth surface. However, microscopic analysis of the WC:H layers shows a frequent occurrence of a certain type of structural defects that have major influence on the layer roughness. The defects are conically shaped objects penetrating the layer all the way down to the substrate, being covered with a spherical cap on the top of the layer. The lateral dimensions of the defects vary from several hundreds of nanometers to a few micrometers.To study these defects we prepared several layers at various conditions and analysed them by different methods, such as SEM, FIB, EDX, AFM and Raman spectroscopy. We will discuss the structure of the defects and influence of the preparation conditions on their growth to find the way to control their occurence in the layer.

The effect of defects on the cyclic behavior of polymeric 3D kirigami structures

Recent advances in the assembly of three-dimensional (3D) structures driven by compressive buckling have provided an opportunity to exploit the capability in a broad range of engineering applications. These include microelectromechanical systems, energy storage, and wearable electronic devices. The occurrence of defects during fabrication and assembly, or during operation could impact the performance of the devices. Herein, we investigate the mechanical cycling of structures with different types of structural defects, including the presence of a pre-existing crack, structures with a thinner leg, and a pre-buckled leg. Studies of compressive cycling response of these microscale 3D polymer-based kirigami architectures revealed stiffening behavior for both defective and non-defective structures. Structural densification, developed internal stress, and deformation of the elastomer substrate were the reasons for stiffening. Cyclic compression was performed to 50% and extreme condition of 100 % of the initial height using in-situ scanning electron microscopy. The structures were found to achieve stable hysteretic cycling with steady-state mechanical response after a number of cycles. The deformation behavior, the structure stability under cyclic loading, and the load bearing capability were found to be dependent on the defect type, but they were not catastrophic.