Defect Formation Research Articles

Optimizing microstructure and minimizing defects in laser-arc hybrid additive manufacturing of Al-Cu alloy: the role of laser mode

Recently, laser-arc hybrid additive manufacturing (LAHAM) has emerged as a transformative method for producing lightweight aluminum alloys, valued for its advantageous surface quality and mechanical properties. In this study, the effect of various laser modes on macro morphology, defect formation, microstructure evolution, and mechanical properties of Al-Cu alloy were investigated. At a laser power threshold of 1.5 kW, the transition from conduction mode to keyhole mode was observed. When the keyhole formed, the molten metal exhibited enhanced fluidity, resulting in smoother surfaces and more uniform spreading. As laser power increased, although hydrogen-induced pores (HIP) were notably reduced, the keyhole-induced pores (KIP) began to appear. During subsequent depositions, the intense reheating effects from laser facilitated a transformation from reticular eutectics (RE) along grain boundaries to granular eutectics (GE). Additionally, recrystallization and formation of Σ3 coincidence site lattice (CSL) boundaries were restricted due to the reduced residual stress caused by moderating cooling rates, alleviating stress concentration near pores during deformation. Therefore, optimal results were achieved in conduction mode at a laser power of 1 kW, achieving highest tensile strengths of 269.5 MPa and 260.1 MPa, and elongations of 19.6% and 13.8% in horizontal and vertical directions, respectively.

Insight into the influence of plasma-assisted heteroatom doping and defect formation in enhancing the areal capacitance of carbon nanowalls

Insight into the influence of plasma-assisted heteroatom doping and defect formation in enhancing the areal capacitance of carbon nanowalls

Bridging behavior of molten pool and its effect on defects formation in ultra-thin sheets edge welding by micro-plasma arc

Bridging behavior of molten pool and its effect on defects formation in ultra-thin sheets edge welding by micro-plasma arc

Study of defect formation mechanisms in Li2ZrO3/MgLi2ZrO4 ceramics using EPR spectroscopy

Study of defect formation mechanisms in Li2ZrO3/MgLi2ZrO4 ceramics using EPR spectroscopy

Enhancing the ferroelectric performance of Hf0.5Zr0.5O2films by optimizing the incorporation of Al dopant.

HfO2-based ferroelectric (FE) thin films have gained considerable interest for memory applications due to their excellent properties. However, HfO₂-based FE films face significant reliability challenges, especially the wake-up and fatigue effects, which hinder their practical application. In this work, we fabricated 13.5 nm-thick Al-doped Hf0.5Zr0.5O2(HZO) films with both uniform (UD) and optimized (OD) Al distributions, systematically investigating the effects of Al doping distribution on their ferroelectric and endurance performances. After optimizing the Al distribution, the OD samples exhibit significantly enhanced ferroelectricity, with a robust remnant polarization (2Pr) of 53.7 μC/cm2. Besides, compared to the undoped and UD HZO films, the OD samples exhibit enhanced dielectric performance, with lower leakage currents and higher breakdown voltages, suggesting that the optimized distribution suppresses oxygen vacancy generation and mitigates defect formation. Furthermore, the OD samples maintain a large 2Pr of 40.4 μC/cm2after 108, which can be rejuvenated back to 50.7 μC/cm2by higher voltage cycling. The enhanced dielectric performances and reversible phase transitions during cycling underline the potential of Al-doped HZO films with optimized distribution as reliable, long-endurance FE materials, advancing the development of HfO₂-based FE devices for future memory applications.&#xD.

Electrophysiological Characterization of Monoolein-Fatty Acid Bilayers.

Understanding the evolution of protocells, primitive compartments that distinguish self from nonself, is crucial for exploring the origin of life. Fatty acids and monoglycerides have been proposed as key components of protocell membranes due to their ability to self-assemble into bilayers and vesicles capable of nutrient exchange. In this study, we investigate the electrophysiological properties of planar bilayers composed of monoglyceride and fatty acid mixtures, using a droplet interface bilayer system. Three fatty acids with varying hydrocarbon chain lengths─oleic acid (C18), palmitoleic acid (C16), and myristoleic acid (C14)─in combination with monoolein (C18) are examined to evaluate the influence of chain length and composition on bilayer stability, thickness, and ion permeability. The results show that pure monoolein bilayers exhibit enhanced ion permeability compared to phospholipid bilayers, which are characteristic of modern cellular membranes. Furthermore, the incorporation of fatty acids into monoolein bilayers destabilizes the membrane structure and further increases ion permeability. We consider that this increased permeability is likely driven by three molecular characteristics. First, the wedge-like shape of monoolein may disrupt bilayer packing and induce transient pore formation. Second, the rapid flip-flop of fatty acids between bilayer leaflets likely facilitates ion transport. Third, the chain-length mismatch between monoolein and myristoleic acid further destabilizes the bilayer, promoting the formation of structural defects. These findings suggest that compositional motifs in monoglyceride-fatty acid bilayers may provide an alternative ion transport mechanism, such as the flip-flop of amphiphilic molecules, in early protocell membranes before the evolution of protein-based transporters.

Monolayer MoS2 with S vacancy defects doped with Group V non-metallic elements (N, P, As): a first-principles study.

This study systematically investigated the effects of single S-atom vacancy defects and composite defects (vacancy combined with doping) on the properties of MoS2 using density functional theory. The results revealed that N-doped S-vacancy MoS2 has the smallest composite defect formation energy, indicating its highest stability. Doping maintained the direct band gap characteristic, with shifts in the valence band top. The Fermi level slightly shifted down in N- and P-doped systems, with N-doped MoS2 showing a larger increase in valence band top energy. Doping also significantly altered the density of states at the Fermi level and weakened the dielectric properties of MoS2. The maximum dielectric peaks of doped systems appeared near 2.7 eV with reduced intensities and red-shifted energies. Optical properties were significantly changed, with decreased reflectance, narrower reflectance spectra, and blue-shifted absorption spectra. These findings suggest that introducing composite defects can effectively reduce the forbidden bandwidth of MoS2, enhancing electrical conductivity. This research provides theoretical guidance for novel material design and offers insights into composite defect behavior in other two-dimensional materials. The Materials-Studio CASTEP module was used to calculate density functional theory (DFT). A plane wave ultrasoft pseudopotential is used to optimize the crystal structure, and the generalized gradient approximation (GGA) in the form of Perdew-Burke-Ernzerhof (PBE) is used to characterize the exchange correlation energy. After the convergence test, the truncation energy and dot settings were finally selected to be 450 eV and 3 × 3 × 1, respectively, the convergence accuracy was set to 1.0e-5eV/atom, and the convergence criterion for the interatomic interaction force was 0.02 eV/Å. The parameters were all at or better than the accuracy settings. The vacuum layer between the layers wasset to 18 Å to avoid interactions caused by the periodic calculation method.

Exploring parameter dependence of atomic minima with implicit differentiation

Interatomic potentials are essential to go beyond ab initio size limitations, but simulation results depend sensitively on potential parameters. Forward propagation of parameter variation is key for uncertainty quantification, whilst backpropagation has found application for emerging inverse problems such as fine-tuning or targeted design. Here, the implicit derivative of functions defined as a fixed point is used to Taylor-expand the energy and structure of atomic minima in potential parameters, evaluating terms via automatic differentiation, dense linear algebra or a sparse operator approach. The latter allows efficient forward and backpropagation through relaxed structures of arbitrarily large systems. The implicit expansion accurately predicts lattice distortion and defect formation energies and volumes with classical and machine-learning potentials, enabling high-dimensional uncertainty propagation without prohibitive overhead. We then show how the implicit derivative can be used to solve challenging inverse problems, minimizing an implicit loss to fine-tune potentials and stabilize solute-induced structural rearrangements at dislocations in tungsten.

Defect Migration and Phase Transformations in Two-Dimensional Iron Chloride inside Bilayer Graphene.

The intercalation of metal chlorides, and particularly iron chlorides, into graphitic carbon structures has recently received lots of attention, as it can not only protect this two-dimensional (2D) magnetic system from the effects of the environment but also substantially alter the magnetic, electronic, and optical properties of both the intercalant and host material. At the same time, intercalation can result in the formation of structural defects or defects can appear under external stimuli, which can affect materials performance. These aspects have received so far little attention in dedicated experiments. In this study, we investigate the behavior of atomic-scale defects in iron chlorides intercalated into bilayer graphene by using scanning transmission electron microscopy and first-principles calculations. We observe transformations between the FeCl2 and FeCl3 phases and elucidate the role of defects in the transformations. Specifically, three types of defects are identified: Fe vacancies in FeCl2 domains and Fe adatoms and interstitials in FeCl3 domains, each exhibiting distinct dynamic behaviors. We also observed a crystalline phase with an unusual stoichiometry of Fe5Cl18 that has not been reported before. Our findings not only advance the understanding of intercalation mechanism of 2D materials but also highlight the profound impact of atomic-scale defects on their properties and potential technological applications.

Electron Microscopy Reveals Inhomogeneous Adsorption of Iodine and Concurrent Defect Formation in a Metal-Organic Framework.

Adsorption behaviors are typically examined through adsorption isotherms, which measure the average adsorption amount as a function of partial pressure or time. However, this method is incapable of identifying inhomogeneities across the adsorbent, which may occur in the presence of strong intermolecular interactions of the adsorbate. In this study, we visualize the adsorption of molecular iodine (I2) in the metal-organic framework material MFM-300(Sc) using high-resolution scanning transmission electron microscopy (STEM). Our observations demonstrate that, counterintuitively, I2 adsorption in MFM-300(Sc) occurs in an inhomogeneous manner, regardless of the I2 uptake level. Even at adsorption saturation, corresponding to an average of 23 iodine atoms per unit cell, MOF channels with significantly varying iodine contents─from nearly empty to densely filled─coexist. Image simulations suggest that the most densely packed I2 may locally form the previously proposed triple-helix structure, corresponding to up to 142 iodine atoms per unit cell. Furthermore, STEM imaging reveals that I2 adsorption can induce the formation of structural defects, such as edge dislocations and stacking faults, within the MOF framework. These defects persist even after the complete removal of I2 molecules. Additionally, we have developed a surfactant-capping strategy to minimize the release of adsorbed I2 from MFM-300(Sc) and validated its effectiveness using STEM imaging.

Surface Integrity and Machining Mechanism of Al 7050 Induced by Multi-Physical Field Coupling in High-Speed Machining

Improving the surface quality and controlling the microstructure evolution of difficult-to-cut materials are always challenges in high-speed machining (HSM). In this paper, surface topography, defects and roughness are assessed to characterize the surface features of 7050 aluminum alloy (Al 7050) under HSM conditions characterized by high temperature, strain and strain rate. Based on multi-physical field coupling, the mechanism of microstructure evolution of Al 7050 is investigated in HSM. The results indicate that the surface morphology and roughness of Al7050 during HSM are optimal at fz = 0.025 mm/z, and the formation of surface defects (adherent chips, cavities, microcracks, material compression and tearing) in HSM is mainly affected by thermo-mechanical coupling. Significant differences are observed in the microstructure of different machined subsurfaces by electron backscatter diffraction (EBSD) technology, and high cutting speeds and high feed rates contributed to recrystallization. The crystallographic texture types on machined subsurface are mainly {110}<112> Brass texture, {001}<100> Cube texture, {123}<634> S texture and {124}<112> R texture, and the crystallographic texture type and intensity are significantly affected by multi-physical field coupling. The elastic–plastic deformation and microstructural evolution of Al7050 alloy during the HSM process are mainly influenced by the coupling effects of multiple physical fields (stress–strain field and thermo-mechanical coupling field). This study reveals the internal mechanism of multi-physical field coupling in HSM and provides valuable enlightenment for the control of microstructure evolution of difficult-to-cut materials in HSM.

Ambient‐Printed Methylammonium‐Free Perovskite Solar Cells Enabled by Multiple Molecular Interactions

AbstractThe ambient printing of high‐performance and stable perovskite solar cells (PSCs) is crucial for enabling low‐cost and energy‐efficient industrial fabrication. However, producing high‐quality perovskite films via ambient printing remains challenging due to direct exposure to air, which easily induces additional stacking defects and triggers perovskite degradation compared to films fabricated by traditional spin‐coating under inert conditions. Here, a multiple molecular interaction strategy is introduced to address this challenge by incorporating a 2‐thiazole formamidine hydrochloride (TC) additive, effectively suppressing defect formation during ambient printing. The specific interactions between TC and precursor components, i.e., multiple hydrogen bonds and coordination interactions, could promote the crystallization of α‐phase perovskites and reduce cation and anion vacancies simultaneously when drying in air. These endows high‐quality ambient‐printed perovskite films with large crystalline grains with eliminated nanovoids and low trap‐densities, which improve charge carrier dynamics and prevent perovskite decomposition and hydration under thermal/humidity stress during long‐term annealing/ambient storage. The unencapsulated PSCs show a high efficiency of 23.72% with good stability, i.e., realizing 92% and 95% efficiency retention after 672 h of annealing at 85 °C in a N2 atmosphere and after 2088 h of storage in ambient air.

Prediction Model for Flake Line Defects in Metallic Injection Molding: Considering Skin-Core Velocity and Alignment.

Metallic injection molding combines aluminum flake metallic pigments with polymers to directly produce components with metallic luster, improving production efficiency and reducing environmental impact. However, flake line defects that occur in regions where ribs or flow paths intersect remain a significant challenge. This study proposes a velocity model that considers the flow characteristics between the surface and core layers and an alignment model that incorporates the orientation of aluminum flakes to predict appearance defects. Through this approach, the mechanisms of appearance defect formation were systematized, and the appearance defects caused by flow velocity differences between the surface and core layers, flake alignment uniformity, and reflection angles were visualized. Both prediction models demonstrated a 50% prediction accuracy, successfully identifying two out of four observed defects. This research addresses the limitations of previous prediction methods, which only considered the surface layer, by introducing a novel approach that accounts for the core layer. It is expected to contribute to reducing defects and improving quality in industries requiring high-quality metallic appearances.

Recent advances in synthesis and application of Magnéli phase titanium oxides for energy storage and environmental remediation.

High-temperature reduction of TiO2 causes the gradual formation of structural defects, leading to oxygen vacancy planar defects and giving rise to Magnéli phases, which are substoichiometric titanium oxides that follow the formula Ti n O2n-1, with 4 ≤ n ≤ 9. A high concentration of defects provides several possible configurations for Ti4+ and Ti3+ within the crystal, with the variation in charge ordered states changing the electronic structure of the material. The changes in crystal and electronic structures of Magnéli phases introduce unique properties absent in TiO2, facilitating their diverse applications. Their exceptional electrical conductivity, stability in harsh chemical environments and capability to generate hydroxyl radicals make them highly valuable in electrochemical applications. Additionally, their high specific capacity and corrosion resistance make them ideal for energy storage facilities. These properties, combined with excellent solar light absorption, have led to their widespread use in electrochemical, photochemical, photothermal, catalytic and energy storage applications. To provide a complete overview of the formation, properties, and environmental- and energy-related applications of Magnéli phase titanium suboxides, this review initially highlights the crystal structure and the physical, thermoelectrical and optical properties of these materials. The conventional and novel strategies developed to synthesise these materials are then discussed, along with potential approaches to overcome challenges associated with current issues and future low-energy fabrication methods. Finally, we provide a comprehensive overview of their applications across various fields, including environmental remediation, energy storage, and thermoelectric and optoelectronic technologies. We also discuss promising new directions for the use of Magnéli phase titanium suboxides and solutions to challenges in energy and environment-related applications, and provide guidance on how these materials can be developed and utilised to meet diverse research application needs. By making use of control measures to mitigate the potential hazards associated with their nanoparticles, Magnéli phases can be considered as versatile materials with potential for next generation energy needs.

Investigation of the photocatalytic potential of C/N-co-doped ZnO nanorods produced via a mechano-thermal process.

Doping in pure materials causes vital alterations in opto-electrical and physicochemical characteristics, which enable the produced doped material to be highly efficient and effective. The current work focused on the synthesis of C/N-co-doped-ZnO nanorods via a facile, eco-friendly, and solvent-free mechano-thermal approach. The synthesized C/N-co-doped ZnO nanorods were employed for the photocatalytic decay of methylene blue (MB) and brilliant cresyl blue (BCB) dyes, and their degradation capability was compared with that of pure ZnO nanoparticles prepared via a precipitation approach. The FESEM findings confirmed the formation of rod-shaped nanostructures of co-doped ZnO nanoparticles, and EDX and XPS results revealed the successful doping of C and N atoms in ZnO lattices. The XRD and XPS results substantiated that N-doping in the ZnO lattice followed substitutional and interstitial mechanisms, while C-doping followed a substitutional pathway. The co-doped ZnO nanorods exhibited highly enhanced degradation potential toward both MB (∼99%) and BCB (∼98%) dyes upon exposure to visible light for 60 min in a basic medium at pH = 10 owing to factors such as formation of new energy states within the band gap of ZnO, delayed recombination of photogenerated charge carriers, and formation of lattice defects in the ZnO lattice due to C and N doping. The MB and BCB dyes photodegraded at degradation rates of 637.23 × 10-4 and 775.25 × 10-4 min-1, respectively, and the photodegradation process showed good agreement with the pseudo-first-order kinetics in the presence of co-doped ZnO nanorods under visible light illumination. The ˙O2 - radicals were the key reactive species involved in the decay of MB and BCB dyes over co-doped ZnO, as confirmed via scavenger studies, and the C/N-co-doped ZnO nanorods retained approximately 90% and 91% efficiencies for BCB and MB dyes, respectively, after three successive cycles of reuse, which confirmed their good stability and reusability under visible light.

Influence of Process Parameter and Build Rate Variations on Defect Formation in Laser Powder Bed Fusion SS316L.

Laser powder bed fusion (LPBF) is an additive manufacturing process that has gained interest for its material fabrication due to multiple advantages, such as the ability to print parts with small feature sizes, good mechanical properties, reduced material waste, etc. However, variations in the key process parameters in LPBF may result in the instantiation of porosity defects and variation in build rate. Particularly, volumetric energy density (VED) is a variable that encapsulates a number of those parameters and represents the amount of energy input from the laser source to the feedstock. VED has been traditionally used to inform the quality of the printed part but different values of VED are presented as optimal values for certain material systems. An optimal VED value can be maintained by changing the key process parameters so that various combinations yield a constant value. In this study, an optimal constant VED value is maintained while printing SS316L with variable key processing parameters. Porosity analysis is performed using optical microscopy, as well as X-ray computed tomography, to reveal the volume density and distribution of those pores. Two primary defect categories are identified, namely lack of fusion and porosity induced by balling defects. The findings indicate that, even at optimal VED, variations in process parameters can significantly influence defect type, underscoring the sensitivity of defect formation to the variation of these parameters. Furthermore, a minor change in the build rate, driven by adjustments in process parameters, was found to influence defect categories. These findings emphasize that fine tuning the process parameters and build rate is essential to minimize defects. Finally, fiducial marks have been identified as a source of unintentional porosity defects. These results enable the refinement of process parameters, ultimately optimizing LPBF to achieve enhanced material density and expedite the printing.

Abdominal wound dehiscence after appendectomy during pregnancy treated by negative pressure wound therapy with subsequent vaginal delivery: A case report and literature review.

Negative pressure wound therapy (NPWT) is a very effective method in the treatment of dehiscent, infected, and non-healing wounds. Difficult wound healing occurs especially in late pregnancy due to the rapid enlargement of the uterus and the constantly increasing tension of the entire abdominal wall. In cases of dehiscence of the surgical wound during pregnancy, proper subsequent treatment is needed, where it is necessary to consider the safety of the mother as well as the fetus. We report the case of a 30-week pregnant patient who was surgically treated for acute appendicitis in pregnancy with an open appendectomy approach. Postoperative complications resulted in wound dehiscence with complete defect in fascia, which was treated with negative V.A.C. ATS® Therapy System. The therapy was started in the 30th week of pregnancy and continued until delivery with regular check-ups and regular redressing of the vacuum-assisted closure (VAC) system. At 38 weeks of pregnancy, the patient delivered vaginally with continued VAC therapy insitu. The final suture took place 3 days after vaginal delivery. Non-healing wounds with abdominal wall defects should be treated using a multidisciplinary approach, and NPWT can be used. This therapy can also be used during pregnancy. Vaginal delivery is preferred because it reduces the risk of further formation or deepening of the abdominal wall defect after a sufficient time interval from the start of the treatment. This complex case with a literature review of surgical complications in pregnancy treated with NPWT therapy highlights the advantage of a multidisciplinary approach.

Effect of dopants and surface oxides on the electronic properties of dislocations in p-type SiC

Abstract Understanding the electronic properties of dislocations is key to tailoring the properties of silicon carbide (SiC)-based electronic devices. By combining the Kelvin probe force microscopy (KPFM) analysis and first-principles calculations, we investigate the effect of aluminum (Al) dopants and surface oxides on the electronic properties of dislocations in p-type SiC. It is found that dislocations, including threading screw dislocations (TSDs), threading edge dislocations (TEDs), and basal plane dislocations (BPDs) create deep acceptor-like states in p-type SiC. The defect levels move upwards in the order of BPD, TED and TSD, which closely relates with the lattice distortion of dislocations. Interestingly, we find that the defect levels of dislocations are higher than that of Al in p-type SiC. First-principles calculations indicate that the defect formation energies of Al dopants at the cores of dislocations are higher than those in the perfect region of p-type SiC, as a result of the steric effect. This indicates that the concentration of Al acceptors at the dislocation cores is lower than that in the perfect region, resulting in the higher defect level positions of dislocations in p-type SiC. Additionally, we find that surface oxidation reduces the difference of defect-level positions between dislocations and the perfect region of p-type SiC, which paves the way for tailoring the electronic properties of dislocations in p-type SiC.

Low‐Dimensional Structure Modulation in Ag8SnSe6 for Enhanced Thermoelectric Performance

AbstractTernary liquid‐like thermoelectric materials have garnered significant attention due to their ultra‐low lattice thermal conductivity. Among these, Ag8SnSe6 stands out for its exceptionally low sound velocity and thermal conductivity. However, the inherent poor electrical conductivity and suboptimal thermoelectric properties of Ag8SnSe6 necessitate further improvement. Here, a novel approach is initiated to enhance the thermoelectric properties of Ag8SnSe6 by combining low‐dimensionalization with intrinsic doping. For the first time, this work successfully synthesizes single‐phase Ag8SnSe6 nanocrystals, ≈10 nm in size, with the correct phase and composition using a robust and reliable colloidal method. This approach represents a significant improvement over previous reports on this material. Reducing the crystal domains of Ag8SnSe6 to the nanoscale induces quantum confinement effects, increasing the density of states near the Fermi surface. It also introduces additional grain boundaries, which lower the lattice thermal conductivity and simplify structural design. Moreover, incorporating small amounts of Sn nanopowder into the Ag8SnSe6 nanocrystals before consolidation further enhances the thermoelectric performance. Sn acts as a donor dopant, increasing the electronic concentration while at the same time improving their mobility by reducing interface barriers, thus significantly improving the material transport properties. Additionally, the presence of Sn leads to the formation of point defects, dislocations, and secondary phases, which increase phonon scattering and further reduce the thermal conductivity. Through this synergistic optimization, the figure of merit shows a significant increase across a wide temperature range. Overall, a strategy is presented for the controlled preparation of Ag8SnSe6 nanocrystals, the decoupling of their electrical and thermal transport, and the practical application of this material to thermoelectric single‐leg modules.

SARS-CoV-2 FP1 Destabilizes Lipid Membranes and Facilitates Pore Formation.

SARS-CoV-2 viral entry requires membrane fusion, which is facilitated by the fusion peptides within its spike protein. These predominantly hydrophobic peptides insert into target membranes; however, their precise mechanistic role in membrane fusion remains incompletely understood. Here, we investigate how FP1 (SFIEDLLFNKVTLADAGFIK), the N-terminal fusion peptide, modulates membrane stability and barrier function across various model membrane systems. Through a complementary suite of biophysical techniques-including electrophysiology, fluorescence spectroscopy, and atomic force microscopy-we demonstrate that FP1 significantly promotes pore formation and alters the membrane's mechanical properties. Our findings reveal that FP1 reduces the energy barrier for membrane defect formation and stimulates the appearance of stable conducting pores, with effects modulated by membrane composition and mechanical stress. The observed membrane-destabilizing activity suggests that, beyond its anchoring function, FP1 may facilitate viral fusion by locally disrupting membrane integrity. These results provide mechanistic insights into SARS-CoV-2 membrane fusion mechanisms and highlight the complex interplay between fusion peptides and target membranes during viral entry.