Formation Mechanism Of Defects Research Articles

Self-assembled micro-patterns in uphill-diffusion solution system.

In this work we present self-organized regular patterns in a solution system through uphill-diffusion. Micrometer thick organic semiconductor solution is sandwiched between a substrate and cover-plate. Self-assembled regular patterns can be observed on the substrate after solvent evaporation. Different micro-patterns and pattern defects were displayed and analyzed. Mechanisms of defect formation, mode selection process during patten generation, and pattern sedimentation onto substrate from solution were proposed. Organic thin film transistors were fabricated with the assembled line patterns which demonstrate a promising way to produce patterned micro/nano materials.

Formation Mechanism and Prevention of Cu Undercut Defects in the Photoresist Stripping Process of MoNb/Cu Stacked Electrodes

The Cu undercut is a recently discovered new defect generated in the wet stripping process of MoNb/Cu gate stacked electrodes for thin-film transistors (TFTs). The formation mechanism and preventive strategy of this defect were identified and investigated in this paper. The impact of stripper concentration and stripping times on the morphology and the corrosion potential (Ecorr) of Cu and MoNb were studied. It is observed that the undercut is Cu tip-deficient, not the theoretical MoNb indentation, and the undercut becomes severer with the increase in stripping times. The in-depth mechanism analysis revealed that the abnormal Cu undercut was not ascribed to the galvanic corrosion between MoNb and Cu but to the local crevice corrosion caused by the corrosive medium intruding along the MoNb/Cu interface. Based on this newly found knowledge, three possible prevention schemes (MoNiTi (abbreviated as Mo technology development (MTD) layer/Cu), MoNb/Cu/MTD, and MoNb/Cu/MoNb) were proposed. The experimental validation shows that the Cu undercut can only be completely eliminated in the MoNb/Cu/MTD triple-stacked structure with the top MTD layer as a sacrificial anode. This work provides an effective and economical method to avoid the Cu undercut defect. The obtained results can help ensure TFT yield and improve the performance of TFT devices.

Effect of Eu Ions Concentration in Y2O3-Based Transparent Ceramics on the Electron Irradiation Induced Luminescence and Damage

Eu3+-doped Y2O3-based luminescent materials can be used as a scintillator for electron or high energy β-ray irradiation, which are essential for applications such as electron microscopy and nuclear batteries. Therefore, it is essential to understand their defect mechanisms and to develop materials with excellent properties. In this paper, Y2O3-based transparent ceramics with different Eu3+ doping concentrations were prepared by solid-state reactive vacuum sintering. This series of transparent ceramic samples exhibits strong red emission under electron beam excitation at the keV level. However, color change appears after the high-energy electron irradiation due to the capture of electrons by the traps in the Y2O3 lattice. Optical transmittance, laser-excited luminescence, X-ray photoelectron spectroscopy (XPS), and other analyses indicated that the traps, or the color change, mainly originate from the residual oxygen vacancies, which can be suppressed by high Eu doping. Seen from the cathodoluminescence (CL) spectra, higher doping concentrations of Eu3+ showed stronger resistance to electron irradiation damage, but also resulted in lower emissions due to concentration quenching. Therefore, 10% doping of Eu was selected in this work to keep the high emission intensity and strong radiation resistance both. This work helps to enhance the understanding of defect formation mechanisms in the Y2O3 matrix and will be of benefit for the modification of scintillation properties for functional materials systems.

Formation mechanism of pore defects and surface ripples under different process parameters via laser powder bed fusion by numerical simulation and experimental verification

Formation mechanism of pore defects and surface ripples under different process parameters via laser powder bed fusion by numerical simulation and experimental verification

Analysis of the gas pipeline defects formation mechanism as a result of arc discharge impact on the pipe wall

The article presents an analysis of the formation possibility through defects in a gas pipeline as a result of short-term exposure to an arc discharge. The results of metallography, electron microscopy, elemental analysis, as well as the modeling results, confirming the formation possibility through defects in a 7 mm thick gas pipeline wall during an exposure to an arc discharge of less than 2 seconds are presented.

Study on the formation and corrosion mechanism of black spot defects on the surface of industrial continuously hot-dip galvanized Zn-2Al-1.5Mg coating

Study on the formation and corrosion mechanism of black spot defects on the surface of industrial continuously hot-dip galvanized Zn-2Al-1.5Mg coating

Effect of the N-doping concentration on the formation of the wide carrot defect in 4H-SiC homoepitaxial layer grown by trichlorosilane (TCS) as silicon precursor

The effect of epilayer growth system, growth rate and N-doping concentration on the formation of the wide carrot defects in 4H-SiC homoepitaxial layer was investigated in this work. We found that the wide carrot defect formed on 4H-SiC epilayer only with low N-doping concentration of 5 × 1014 cm−3 grown by the SiHCl3+C2H4+H2 (TCS) system, which is different with the previous reports on the SiH4+C3H8+H2 growth system that can form such defect regardless of N-doping concentration. Besides, such wide carrot defect was never found on high speed growth of epilayer surface grown by TCS growth system. The morphology and structure of wide carrot defects were characterized by optical microscope (OM), micro-photoluminescence (PL) spectroscopy, atomic force microscope (AFM) and molten KOH etching. We speculate that the amount of wide carrot defects is related with the basal plane dislocations (BPDs) density which depends on the epitaxial growth system, growth rate of epilayer and the N-doping concentration. The formation mechanism and elimination methods of these wide carrot defects were proposed.

Influence of applied tensile/compressive stress on He-irradiated SiC: Examining defect evolution through experimental investigation and DFT simulations

This study investigates the effects of applied tensile and compressive stresses on the evolution of defects in He-irradiated silicon carbide (SiC) materials. By combining experimental studies with density-functional theory (DFT) simulations, we systematically analyzed the microstructural changes and defect formation mechanisms in SiC under stress. The research focused on He irradiation of SiC at 750 °C, with a fluence of 1 × 101⁷ He/cm2. The results revealed that the strain resulting from radiation damage depends on the applied stress during irradiation. Moreover, the formation of platelets is influenced by this applied stress: tensile stress promotes platelet growth, while compressive stress inhibits it. DFT simulations further supported these experimental findings by showing that under tensile strain, both carbon vacancies (Cv) and He atoms exhibit low energy barriers for migration. This phenomenon facilitates platelet growth, aligning well with the observations made in the experiments. However, when considering applications like semiconductor thin film transfer, such as the Smart-cut technique, He implantation under tensile stress can actually be advantageous. This approach enables the use of lower He fluence, which in turn reduces the overall cost of the operation. By strategically leveraging the effects of tensile stress on He implantation, it becomes possible to optimize processes like Smart-cut for more efficient and cost-effective thin film transfer in semiconductor manufacturing.

Online vibration monitoring using laser vibrometer and acoustic emission techniques in robotic milling CFRP composites

Carbon fiber reinforced polymer (CFRP) material has superior mechanical properties, often utilized in the aerospace industry. However, its prone to surface defects such as burrs and delamination under the influence of machining vibration, thereby compromising component quality. This study evaluated the relevant vibration signal features via signal processing methods, and investigated the effect of machining parameters on machining stability during robotic milling of CFRP composite. Specifically, the study assessed machining status by analyzing milling signals and compared surface quality between vibration and stable machining stages, the former corresponds to a larger Sa on the machined surface, with more pronounced profile fluctuations. Machining vibration manifests distinct characteristics in laser vibrometer signals, exhibiting in time-frequency plots with short-term signal enhancements at multiple frequencies. This phenomenon occurs more frequently during entry and exit stages. The results indicated that feed speed has a limited effect on milling stability within the selected parameter range, and severe machining vibration occurred at lower spindle speed (12,000 rpm) and higher milling depth (2 mm). Corresponding surface defects formation mechanisms were discussed, revealing that the formation of uncut burrs at the top was related to axial milling force, while interlayer debonding cracks stemmed from variations in fiber orientation between adjacent layers.

Study of native point defects in Al0.5Ga0.5N by first principles calculations

To explore the formation mechanism of native point defects in high Al content AlGaN film, the first principles methods are applied to study the native point defects in Al0.5Ga0.5N. The different kinds of vacancies, interstitials, and antisites are investigated. The formation energies of Al0.5Ga0.5N with native point defects under different charge states and growth conditions are analyzed and compared. Then, the preferable charge state, donor and acceptor properties of Al0.5Ga0.5N with different native point defects are explicitly obtained. The results show that AlN, GaN, Ali, and VN exhibit donor properties in p-type condition while VGa, VAl, VN, and NGa exhibit acceptor properties and can play roles as compensating center in n-type Al0.5Ga0.5N under metal rich condition. For N rich condition,VGa, VAl, NGa, and NAl are favorable acceptors in n-type Al0.5Ga0.5N. Meanwhile, the charge distribution and bonding state of Al0.5Ga0.5N with native point defects are explored. It is found the N atoms in Ni and NGa form covalent bond and ionic bond with atoms in Al0.5Ga0.5N. Moreover, the band calculation reveals that the removal of N atom in Al0.5Ga0.5N makes the conduction band fatter and the effective masses of electrons increase while the introduction of N point defects make the valence band flatter, increasing the effective masses of holes. Furthermore, the corresponding thermodynamic transition energy levels of defects under different charge states are summarized. It is found that the thermodynamic transitions for VN, Ni, and NAl may likely to happen under certain conditions. The above studies yield a detailed and quantitative description of native point defects in Al0.5Ga0.5N, which helps to get a deeper insight to the growth and doping of AlGaN.

Formation mechanism of cation-vacancy microenvironments and the effect on hydrogen transfer reaction of 5-hydroxymethylfurfural

Two Cu/ZrO2 catalysts defect with different microenvironments and electronic structures (CZ-ag-70 and CZ-va catalysts) were synthesized by the same oxalic-acid-complexation-based method but different heat-treatment methods, and they were used to catalyze the hydrogen-transfer reaction between 5-hydroxymethylfurfural (HMF) and isopropanol. The structure–activity relationship of each catalyst was analyzed, and defect microenvironments were found to have an important influence on the product of the hydrogen-transfer reaction. The CZ-ag-70 catalyst was rich in Cuδ+- VZr+ interfacial sites (the interfacial sites between electron-deficient copper active sites (Cuδ+)) and electron-free zirconium vacancies (VZr+), and it was conducive to the formation of dehydroxylation product 2,5-dimethylfuran (DMF). Specifically, the ca-ag-70 catalyst achieved 100 % HMF conversion and 82.2 % DMF selectivity. On the other hand, the CZ-va catalyst was rich in single-electron zirconium vacancies (VZr∙), and it was conducive to the generation of reductive-etherification product 2,5-bis(propoxymethyl)furan (BPMF) (100 % HMF conversion and 55 % BPMF selectivity). Through X-ray diffraction spectrum (XRD), electron spin resonance (ESR), hydrogen temperature-programmed reduction (H2-TPR), in-situ Fourier-transform infrared spectroscopy (in-situ FTIR), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) analyses, the structure of the CZ-ag-70 catalyst and the mechanism of defect formation in the catalyst were analyzed. The precursor of the CZ-ag-70 catalyst first formed a copper-doped zirconium oxalate substrate. Then, under 500 ℃ reducing atmosphere, the substrate was converted into a copper-doped tetragonal-zirconia carrier, some of the copper species doped into the crystal lattice of the tetragonal-zirconia carrier were reduced, and the copper species migrated to the surface of the carrier, forming Cuδ+- VZr+ interfacial sites. The electrons around the zirconium vacancy of the CZ-ag-70 catalyst are in a completely delocalized state and Cu+ gains electrons which in turn produces Cuδ+- VZr+ interfacial sites.

Analyzing point defect polarization in tungsten and tungsten carbide under high gamma irradiation for radiation shielding applications

In this study, polycrystalline tungsten and tungsten carbide samples were irradiated with gamma rays at energies of 1.17 MeV and 1.33 MeV, respectively. The irradiation was performed using an “MRX-γ-25 M” radiation camera with an activity of approximately 6.54 Gy/s. Doppler positron spectroscopy (DPS) and positron lifetime spectroscopy (PALS) were utilized to investigate the mechanisms of defect formation in the polycrystalline structure of tungsten samples at different doses of gamma irradiation. In the initial tungsten sample, a significant number of free monovacancy (1 V) clusters were present. An increase in the positron lifetime component τ1 was observed with increasing gamma irradiation, accompanied by a decrease in its intensity. The τ2 value (218 ± 2 ps) suggests the presence of divacancies with a considerable intensity (∼20%). As the gamma dose accumulated, a dynamic evolution of structural defects was evident. The tungsten carbide (WC) samples displayed greater plasticity in response to increasing gamma irradiation doses. Changes in the void volume ratio within the samples were recorded as the gamma dose increased, and movement of these voids towards the surface was observed. Additionally, the operational limits of gamma-irradiated tungsten were assessed, determining a functional threshold of up to 3.378 MGy. This study provides valuable insights into the defect dynamics and structural changes in tungsten and tungsten carbide under gamma irradiation, contributing to the understanding of their behavior in radiation environments.

Effect of Al doping on structural and optical properties of atomic layer deposited ZnO thin films

In this work, zinc oxide (ZnO) and aluminum-doped ZnO (AZO) thin films with varying Al contents were grown via atomic layer deposition on Si and glass substrates. The structural and optical properties of ZnO and AZO thin films were investigated using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), photoluminescence (PL), and ultraviolet-visible spectroscopy. While undoped ZnO had a wurtzite crystal structure, Al2O3 layers altered the crystal structure depending on the Al content. With the increasing number of Al2O3 monolayers, the γ- Al2O3 structure became more prominent, and ZnO peaks were completely suppressed when the Zn ratio reached 10:1 and beyond. SEM images revealed that the thin films homogeneously covered the entire substrate surface. EDS mapping showed a uniform distribution of Zn, Al, and O in the structure. According to the XPS results, the thin films displayed significant peak intensities corresponding to the main components Zn, O, and Al. Zinc atoms were present only in their oxidized state, not as interstitial atoms. The O 1 s peak could be deconvoluted into three components: the oxygen-zinc bond, the oxygen-aluminum bond, and chemisorbed or OH species. In the AZO samples, a direct correlation was observed between the intensity of the Al 2p peak and the number of Al2O3 layers. Additionally, the calculated elemental ratio of Al increased from 2.582 to 23.955 at.% with more Al2O3 layers. Optical measurements revealed that ZnO and AZO thin films exhibit high transmittance in the visible region. Moreover, introducing Al2O3 layers into the supercycle led to an increasing trend in transmittance. Another improvement in the optical properties was observed as a blue shift in the absorption edge with Al doping, indicating band gap widening. The optical band gap of the ZnO thin films increased from 3.2 to 3.5 eV with Al doping. The origin and concentration of defects were evaluated by deconvoluting the PL spectra. A comparative investigation of the PL spectrum and XPS results revealed variations in defect concentration with deposition parameters and defect formation mechanism was discussed.

Research on the formation and evolution mechanism of cracks in laser stealth dicing of silicon carbide crystals

In this study, to enhance the cutting efficiency and precision of the chip while minimizing waste from cutting damage, molecular dynamics simulation is used to investigate the formation mechanism of defects and cracks of silicon carbide crystals during the laser stealth dicing. The results showed that the high thermal stress generated by the laser scanning induced the production and expansion of cracks. Thus, the crack propagates in the direction of [100], and subsequently forms branches in the directions of [101] and [101‾]. It also can be found that the silicon carbide crystals produced dislocation slip, and the dislocation lines moved along the slip surface, which impeded the crack extension in the directions of [101‾] and [1‾01‾]. In addition, atomic phase transformation and loss is occurred under the high-temperature environment of the laser heating process. Cubic diamond crystal structure atoms are partially transformed into amorphous structure, while a small portion transformed into hexagonal diamond structure. The crystal structural arranged orderliness temporarily increased and then rapidly decreased due to prefabrication defects, and new unknown crystal structures are produced.

Area-Selective Atomic Layer Deposition of Ru Using Carbonyl-Based Precursor and Oxygen Co-Reactant: Understanding Defect Formation Mechanisms.

Area selective deposition (ASD) is a promising IC fabrication technique to address misalignment issues arising in a top-down litho-etch patterning approach. ASD can enable resist tone inversion and bottom-up metallization, such as via prefill. It is achieved by promoting selective growth in the growth area (GA) while passivating the non-growth area (NGA). Nevertheless, preventing undesired particles and defect growth on the NGA is still a hurdle. This work shows the selectivity of Ru films by passivating the Si oxide NGA with self-assembled monolayers (SAMs) and small molecule inhibitors (SMIs). Ru films are deposited on the TiN GA using a metal-organic precursor tricarbonyl (trimethylenemethane) ruthenium (Ru TMM(CO)3) and O2 as a co-reactant by atomic layer deposition (ALD). This produces smooth Ru films (<0.1 nm RMS roughness) with a growth per cycle (GPC) of 1.6 Å/cycle. Minimizing the oxygen co-reactant dose is necessary to improve the ASD process selectivity due to the limited stability of the organic molecule and high reactivity of the ALD precursor, still allowing a Ru GPC of 0.95 Å/cycle. This work sheds light on Ru defect generation mechanisms on passivated areas from the detailed analysis of particle growth, coverage, and density as a function of ALD cycles. Finally, an optimized ASD of Ru is demonstrated on TiN/SiO2 3D patterned structures using dimethyl amino trimethyl silane (DMA-TMS) as SMI.

Unveiling the Effect of Cooling Rate on Grown-in Defects Concentration in Polycrystalline Perovskite Films for Solar Cells with Improved Stability.

Numerous efforts are devoted to reducing the defects at perovskite surface and/or grain boundary; however, the grown-in defects inside grain is rarely studied. Here, the influence of cooling rate on the point defects concentration in polycrystalline perovskite film during heat treatment processing is investigated. With the combination of theoretical and experimental studies, this work reveals that the supersaturated point defects in perovskite films generate during the cooling process and its concentration improves as the cooling rate increases. The supersaturated point defects can be minimized through slowing the cooling rate. As a result, the optimized FAPbI3 polycrystalline films achieve a superior carrier lifetime of up to 12.6 µs and improved stability. The champion device delivers a 25.47% PCE (certified 24.7%) and retain 90% of their initial value after >1100 h of operation at the maximum power point. These results provide a fundamental understanding of the mechanisms of grown-in defects formation in polycrystalline perovskite film.

BRIDGING DATA GAPS: A FEDERATED LEARNING APPROACH TO HEAT EMISSION PREDICTION IN LASER POWDER BED FUSION

Abstract Deep learning has impacted defect prediction in Additive Manufacturing (AM), which is important to ensure process stability and part quality. However, its success depends on extensive training, requiring large, homogenous datasets–remaining a challenge for the AM industry, particularly for small- and medium-sized enterprises (SMEs). The unique and varied characteristics of AM parts, along with the limited resources of SMEs, hampers data collection, posing difficulties in the independent training of deep learning models. Addressing these concerns requires enabling knowledge sharing from the similarities in the physics of the AM process and defect formation mechanisms while carefully handling privacy concerns. Federated learning (FL) offers a solution to allow collaborative model training across multiple entities without sharing local data. This paper introduces an FL framework to predict section-wise heat emission during Laser Powder Bed Fusion (LPBF), a vital process signature. It incorporates a customized Long Short-Term Memory (LSTM) model for each client, capturing the dynamic AM process's time series properties without sharing sensitive information. Three advanced FL algorithms are integrated–FedAvg, FedProx, and FedAvgM–to aggregate model weights rather than raw datasets. Experiments demonstrate that the FL framework ensures convergence and maintains prediction performance comparable to individually trained models. This work demonstrates the potential of FL-enabled AM modeling and prediction where SMEs can improve their product quality without compromising data privacy.

Numerical simulation and experimental investigation of the molten pool evolution and defects formation mechanism of Selective laser melted CuSn20/Diamond composites

Some defects such as small pores, thermal damage of diamond particle and micro-cracks between diamond and metal matrix existed in SLM-fabricated metal-bonded diamond tools. For further application, it is vital to understand the formation mechanism of such defects by SLM-fabricated parameters. In this work, a multiphysics field numerical simulation model based on computational fluid dynamics (CFD) was developed to investigate molten pool evolution and defects formation mechanism for SLM-fabricated CuSn20-bonded diamond composites. From simulation results, the metal particles melt and flow forward under the action of the laser. Also, the presence of diamond particles can obstruct the normal flow of melted CuSn20 fluid. Increasing the laser power can widen and stabilize the molten pool, however, exacerbate the thermal damage of diamond particles. Specially, the migration and marginalisation of the diamond particles during the formation of molten pool were found by simulation and experimental results. Unavoidably, there are obvious gaps in the interfacial bonding region of diamond and CuSn20 due to the comprehensive reasons of thermal gradient, differences in thermophysical properties of two materials and undergo continuous migration and rotational behavior of diamond particles. These findings have potential value for understanding and optimizing the process of SLM-fabricated metal-bonded diamond tools.

Research status of laser powder bed fusion Al–Li alloys and its improvement measures

Laser powder bed fusion (LPBF) Al–Li alloy technology demonstrates adaptability to the development requirements of structural complexity and functional integration, making it a promising area of research in additive manufacturing for the aerospace, defense industry, and other fields. However, challenges such as microstructure anisotropy and metallurgical defects inevitably arise during the LPBF process of lightweight alloys, significantly impeding further enhancements in their formability properties. Some improvement measures offer a viable solution to enhance the microstructure, mitigate metallurgical defects, and optimize residual stress distribution in additive structures, thereby enabling high–performance Al–Li alloy production by LPBF. This paper first introduces the fundamental principle of LPBF and discusses the process of parameter optimization for LPBF Al–Li alloys. It then describes the typical microstructures and common metallurgical defects of LPBF Al–Li alloys, along with examining the evolution process of microstructures and formation mechanism of metallurgical defects. Specifically, it focuses on discussing the influence of Li element on solidification structure. On this basis, it presents the mechanical properties and anisotropy of mechanical properties for LPBF Al–Li alloys. Afterward, a comprehensive review is provided of the current research status regarding LPBF improvement measures, including powder alloying, heat treatment, and other technologies. Emphasis is placed on improvements in microstructure anisotropy and reductions in metallurgical defects through these improvement measures. Finally, this article summarizes the research progress made in LPBF Al–Li alloys and its improvement measures while also prospecting future research work.

A neural-network potential for aluminum

Aluminum and its alloys are most often used as structural materials due to their specific properties, such as low weight, low energy consumption for remelting and the possibility of almost complete processing. This paper utilizes machine learning, specifically the Behler-Parrinello neural network scheme, to develop a powerful potential for studying the underlying mechanisms of deformation, fracture, and defect formation. By surpassing the limitations of first principles calculations, the application of machine-learned potentials (MLP) becomes highly advantageous for describing pure aluminum (Al) in its solid and liquid phases. Specifically, from the generated potential equilibrium, thermodynamic, elastic, and vibrational properties of face-centered cubic (fcc) Al are obtained in very good agreement especially with density functional theory (DFT) results as well as with previous calculations using existing semi-empirical potentials, such as EAM and MEAM, recent machine-learned potentials, and experimental data. Furthermore, our potential proves to accurately reproduce defect formation energies such as previously computed and measured stacking-fault energy curves. Finally, stacking fault profiles as well as key quantities of the liquid phase such as the melting point at ambient pressure, temperature-dependent densities, and radial distribution functions are also calculated in very good agreement with the results from previous theoretical and experimental investigations. Nevertheless, our investigation goes beyond previous studies in proving excellent agreement with experimental data especially of the specific heat and the melting point at very high pressures. The competitive analysis performed in this work thus clearly demonstrates the validity and accuracy of the generated machine-learned potential to describe a wide range of properties of Al at various temperatures and pressures and thereby lays ground for future applications.