Generation Of Crystal Defects Research Articles

Influence of transition metal (Cu) and rare earth metal (Dy) co-doping on spinel zinc ferrite (Cu0.1Dy0.08Zn0.9Fe1.92O4) for improved photocatalytic degradation of industrial effluents

In the present era, design and development of novel, highly stable, easily and magnetically separable, cost effective, and visible light driven catalytic material for the removal of harmful industrial effluents is of great importance. In this context, facile co-precipitation route was adopted for the synthesis of ZnFe2O4 (ZFO), Cu0.1Zn0.9Fe2O4 (CZFO), Dy0.08ZnFe1.92O4 (DZFO), and Cu0.1Dy0.08Zn0.9Fe1.92O4 (CDZFO) and their fabrication was confirmed by XRD, FTIR, SEM, and UV-Visible spectroscopy. The phase analysis of all designed materials exhibits that there is an increment in the crystallite size of co-doped zinc ferrite (CDZFO) i.e. 11.51 nm as compared to ZFO (10.74 nm), CZFO (10.92 nm), and DZFO (11.41 nm). The optical study shows a significant decrease in bandgap of CDZFO i.e. 1.82 eV as compared to DZFO (1.89 eV), CZFO (2.0 eV), and ZFO (2.14 eV). This decrease in optical bandgap and increase in crystallite size of the CDZFO is due to the quantum confinement effect. The photocatalytic efficiency of pure, doped, and co-doped samples was investigated against organic dye (Congo red), pharmaceutical drug (ibuprofen), and colorless organic compound (benzoic acid). The photocatalytic results reveal that CDZFO showed about ∼90 % degradation of Congo red while ZFO, CZFO, and DZFO showed only 59 %, 70 %, and 79 % respectively. Moreover, CDZFO also showed highest photocatalytic removal efficiency against ibuprofen (88 %) and benzoic acid (74 %) out of all other synthesized materials. The remarkable photodegradation ability of CDZFO for all targeted pollutants could be attributed to the generation of crystal defects in its lattice, its small bandgap, and higher absorption in visible region. Furthermore, the recyclability experiment confirmed the stability and reusability of the prepared sample.

Investigating Dislocation Arrays Induced by Seed Scratches during PVT 4H-SiC Crystal Growth Using Synchrotron X-Ray Topography

The influence of seed preparation on crystal defect generation is studied by investigating the effect of damage from surface scratches not completely removed during polishing on the seed crystal on the nucleation and evolution of dislocation arrays. Synchrotron X-ray topography is conducted on several wafers sliced from a PVT-grown 4H-SiC boule. Topographic results in conjunction with ray tracing simulation reveal the generation of TSD/TMD and TED arrays associated with the scratches in the newly grown wafer adjacent to the seed. Configuration transformation of those arrays is observed as these opposite-signed dislocation pairs composing the arrays were affected by the overgrowth of macro-steps when propagating into the newly grown crystal.

Influence of pyrite surface defects on xanthate adsorption: A density functional theory perspective

Many scholars have studied the adsorption behavior of various ions and agent molecules on pyrite surfaces based on density functional theory (DFT) calculations, however, the adsorption behavior of pyrite by surface defects has been relatively less studied. In this study, we try to produce defects on the surface of pyrite by hydration and study them systematically. The effects of pyrite surface defects on the molecular adsorption of xanthates were investigated on the atomic scale by combining DFT calculations, and AFM observation methods, respectively. The results indicate that oxygen molecules can indirectly participate in hydration reactions and promote crystal defect generation. In addition, the absence of coordination intensifies the electron transfer of pyrite, which favors the formation of new coordination with xanthates, and the adsorption energy is also reduced. Defects lead to an increase in the number of xanthate molecules at the adsorption site, and the adsorption capacity is also enhanced. The adsorption morphology was analyzed by AFM measurements to confirm the DFT calculation results. The complex interfacial system of sulfide ores was investigated, and it was found that the hydration process of sulfide ores generates surface defects, which further promote xanthate molecules adsorption. The results extend the traditional electrochemical adsorption theory of sulfide ores and provide theoretical support for the study of the molecular dynamics adsorption process on the surface of sulfide ores.

Effect of Nb on microstructure and magnetic decay of sintered NdFeB magnets in NaCl solution

Herein, the influence of Nb on the microstructure and magnetic decay of sintered NdFeB magnets was investigated. The NbFeB and Fe2Nb phases were determined through field emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and selected area electron diffraction. The effects of Nb on the crystal structure of the magnet were studied via electron backscatter diffraction analysis. Laser scanning confocal microscopy, a pulsed field magnetometer, and a fluxmeter were used to measure the changes in the surface roughness and magnetic properties of the magnet during corrosion. Based on the experimental result, Nb can optimize the distribution of the Nd-rich phase inside the magnet, reduce the generation of crystal defects, refine the grains, and promote the crystal orientation along the [001] direction. During magnet corrosion, the Nb compound captured hydrogen atoms, causing internal lattice distortion and stress concentration in the matrix phase thereby leading to crush. The broken matrix phase adhered to the magnet surface, isolating the magnet from contact with the corrosive solution and improving the corrosion resistance of the magnet. Moreover, Nb can reduce the impact of the surface structure damage on the demagnetization of the magnet during corrosion, thereby lowering magnetic decay.

Relaxation of the Distorted Lattice of 4H-SiC (0001) Surface by Post-Oxidation Annealing

Thermal oxidation of 4H-SiC to grow native-oxide SiO2 is always followed by the generation of crystal defects and lattice distortion. We studied the relaxation of this distorted lattice on thermally-oxidized 4H-SiC surface by performing annealing process with several conditions. The surface distortion could be relaxed partially by annealing under argon, nitrogen monoxide, and H2O gases, confirmed by in-plane X-ray diffractometer. This surface relaxation is possibly induced by the release of oxygen-related defects, as confirmed by thermal desorption analysis. The surface distortion caused by thermal oxidation is due to the existence of oxygen in 4H-SiC lattice, while the relaxation is caused by the migration of the oxygen-related defect structure, and emitted from 4H-SiC surface region as CO molecule.

3D CNN and grad-CAM based visualization for predicting generation of dislocation clusters in multicrystalline silicon

We propose a machine learning-based technique to address the crystallographic characteristics responsible for the generation of crystal defects. A convolutional neural network was trained with pairs of optical images that display the characteristics of the crystal and photoluminescence images that show the distributions of crystal defects. The model was trained to predict the existence of crystal defects at the center pixel of the given image from its optical features. Prediction accuracy and separability were enhanced by feeding three-dimensional data and data augmentation. The prediction was successful with a high area under the curve of over 0.9 in a receiver operating characteristic curve. Likelihood maps showing the distributions of the predicted defects are in good resemblance with the correct distributions. Using the trained model, we visualized the most important regions to the predicted class by gradient-based class activation mapping. The extracted regions were found to contain mostly particular grains where the grain boundaries changed greatly due to crystal growth and clusters of small grains. This technique is beneficial in providing a rapid and statistical analysis of various crystal characteristics because the features of optical images are often complex and difficult to interpret. The interpretations can help us understand the physics of crystal growth and the effects of crystallographic characteristics on the generation of detrimental defects. We believe that this technique will contribute to the development of a better fabrication process for high-performance multicrystalline materials.

Effect of electroshocking treatment on the microstructure and mechanical properties of laser melting deposited near-β Ti-55531 thin-wall

The near-β Ti-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr, wt%) alloy with thin-wall structures were manufactured by laser melting deposition (LMD), and followed by the post-processing of electroshocking treatment (EST). The microstructure evolution before and after EST were characterized via using the scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The results showed that the microstructure of as-deposited specimen was mainly composed of short columnar grains and equiaxed grains, showing a unique structure of alternating short columnar grains-equiaxed grains-short columnar grains. The results of EBSD showed that EST could reduce the orientation concentration and weaken the texture of β phase. XRD results indicated that the α phase content slightly increased after EST. The micro-strain and lattice constant of β phase were changed after EST, which were probably ascribed to the precipitation of α, the generation of crystal defects on α/β interface, and the decrease of texture intensity. The results of mechanical properties indicated that EST could increase the microhardness, the yield strength and the tensile strength, which were due to the variation of microstructure. All results show that EST is an effective approach for optimizing the microstructure and improving the mechanical properties of LMD near-β titanium alloy.

Atomistic Modeling of Ultrashort Pulse Laser-Induced Generation of Crystal Defects

Atomistic Modeling of Ultrashort Pulse Laser-Induced Generation of Crystal Defects

Analysis and Optimization of Defect Generation Due to Mechanical Stress in High-Density SRAM

Static random-access memory (SRAM) is an essential component for realizing large-scale integration (LSI). The future transition to a 48 V DC supply in datacenters and electric vehicles acting as mobile edge servers will increase the demand for a bipolar-complementary metal-oxide semiconductor-double diffused metal-oxide semiconductor with high-capacity SRAM. When we scaled and optimized an SRAM cell from 130 nm nodes to 90 nm nodes, we observed the generation of crystal defects induced by mechanical stress in the p-channel MOS active area that cannot be explained by previous models. We performed simulations using the finite element method to identify the mechanism. In our results, the edge of the narrow active area showed a large deformation compared to the middle of the active area, which can be attributed to compressive stress from the gate electrode and sidewall. The cell layout and sidewall structure were optimized to suppress this defect generation while satisfying reliability requirements, and the design can be extended to 65 nm nodes.

Crystal defects in monocrystalline silicon induced by spot laser melting

Laser processing of monocrystalline silicon has become an important tool for a wide range of applications. Here, we use microsecond spot laser melting as a model experiment to investigate the generation of crystal defects and residual stress. Using Micro-Raman spectroscopy, defect etching, and transmission electron microscopy, we find no dislocations in the recrystallized volume for cooling rates exceeding |dT/dt|=2×107 K/s, and the samples remain free of residual stress. For cooling rates less than |dT/dt|=2×107 K/s, however, the experiments show a sharp transition to a defective microstructure that is rich in dislocations and residual stress. Moreover, transmission electron microscopy indicates dislocation loops, stacking-fault tetrahedra, and voids within the recrystallized volume, thereby indicating supersaturation of intrinsic point defects during recrystallization. Complementing photoluminescence spectroscopy indicates even three regimes with decreasing cooling rate. Spectra of regime 1 do not contain any defect related spectral lines. In regime 2, spectral lines appear related to point defect clusters. In regime 3, the spectral lines related to point defect clusters vanish, but dislocation-related ones appear. We propose a quantitative model explaining the transition from dislocation-free to dislocation-rich recrystallization by means of the interaction between intrinsic point defects and dislocations.

Intrinsic Control in Defects Density for Improved ZnO Nanorod-Based UV Sensor Performance.

Hitherto, most research has primarily focused on improving the UV sensor efficiency via surface treatments and by stimulating the ZnO nanorod (ZNR) surface Schottky barriers. However, to the best of our knowledge, no study has yet probed the intrinsic crystal defect generation and its effects on UV sensor efficiency. In this study, we undertake this task by fabricating an intrinsic defect-prone hydrothermally grown ZNRs (S1), Ga-doped ZNRs (S2), and defect-free microwave-assisted grown ZNRs (S3). The defect states were recognized by studying X-ray diffraction and photoluminescence characteristics. The large number of crystal defects in S1 and S2 had two pronged disadvantages. (1) Most of the UV light was absorbed by the defect traps and the e–h pair generation was compromised. (2) Mobility was directly affected by the carrier–carrier scattering and phonon scattering processes. Hence, the overall UV sensor efficiency was compromised based on the defect-induced mobility-response model. Considering the facts, defect-free S3 exhibited the best UV sensor performance with the highest on/off ratio, the least impulse response time, the highest recombination time, and highest gain-induced responsivity to 368 nm UV light, which was desired of an efficient passive metal oxide-based UV sensor. Our results were compared with the recently published results.

Enhancing magnetic hardness by sonication assisted synthesis of heterometallic carbonato spin-glass Na[Ni(H2O)4Ru2(CO3)4]·3H2O.

Control of magnetic performances of molecular magnets is essential but few efforts have been documented. A green and efficient sonication assisted synthesis of a new heterometallic diruthenium(ii,iii) carbonate, Na[Ni(H2O)4Ru2(CO3)4]·3H2O (1), was carried out by self-assembling in aqueous solution. Compound 1 exhibits spin-glass behavior below ∼5.0 K, and a systematic investigation of the ultrasonic irradiation influence on the powder samples reveals that their coercivity increases from 50 Oe to 743 Oe with the control of ultrasonic power under appropriate conditions.

Reliability investigation on CdTe solar cells submitted to short-term thermal stress

In this paper, we investigate the effect of short-term thermal stresses in CdTe thin film solar cells.The CdTe solar cells under test are manufactured with physical vapour deposition on soda lime glass in superstrate configuration. Different characterization techniques were used to study the reliability of the solar cells. In particular, external quantum efficiency (EQE) and electroluminescence (EL) measurement were applied in order to investigate the physical processes responsible for degradation. Through this analysis, we give a broad overview of degradation effects using both electrical and optical measurement and correlating the results. We show that (i) during short-term thermal stresses a soft degradation occurs, (ii) the series resistance of the cells increases and (iii) degradation is preliminarily ascribed to the generation of crystal defects due to the diffusion of copper or oxygen atoms in the CdTe solar cells.

Controlling Ion-Exchange Balance and Morphology in Cation Exchange from Cu3–xP Nanoplatelets into InP Crystals

Synthesis of colloidal nanocrystals (NCs), which are not readily available via the wet-chemical approach based on arrested precipitation, has often relied on templated growth. Cation exchange, in which guest cations in bulk solution replace host cations in template NCs, has evolved as one of the most powerful examples. Despite its versatility and facileness, there are caveats because most of the cation-exchange processes presuppose the formation of crystalline defects, which are more or less uncontrolled in terms of population and locations. The defect formation is a consequence of the imbalance between extraction and incorporation of host and guest cations. Here, we demonstrate the controlling of ion-exchange balance in the Cu+-to-In3+ cation-exchange reaction of Cu3–xP nanoplatelets (NPLs), which triggers the nanoscale Kirkendall effect, a representative phenomenon of crystal defect generation, clearly shown by morphology change of NPLs. Cation-exchanged NPLs exhibit various morphologies depending on th...

Computational Study of Short-Pulse Laser-Induced Generation of Crystal Defects in Ni-Based Single-Phase Binary Solid–Solution Alloys

Single-phase concentrated solid–solution alloys exhibit enhanced mechanical characteristics and radiation damage resistance, making them promising candidate materials for applications involving an ...

Monolike ingot growth by directional solidification of Solar Grade silicon

In the frame of permanent objective to increase solar cell efficiency and to decrease production cost the monolike ingot process was designed which combine multicrystalline (mc) productivity and monocrystalline structure performances. As a raw material the mc-Solar Grade silicon (SoG-Si) was used because it is less expensive than the Si purified by gas chemical route (Siemens process or equivalent), Usage of the mc-SoG-Si for growing silicon ingots by monolike process should contribute to the ingot and wafer manufacturing cost decrease. SoG silicon using would be developed all the more fast since it enables to produce high efficiency solar cells. It is why the monolike process have been tested and optimized for Kazakhstan mc-SoG silicon. The objective of this work was study of the higher level content impurities influences on the crystal defect generation (mainly dislocations) of the monocrystalline structure. Visual monocrystalline structure, minority carrier lifetime mapping, and photoluminescence techniques were used to study the monolike ingots obtained from Kazakhstan’s mc-SoG silicon.

Nanoscale structures generation within the surface layer of metals with short UV laser pulses

We have completed modeling of a laser pulse influence on a gold target. We have applied a hybrid atomistic-continuum model to analyze the physical mechanisms responsible for the process of nanostructuring. The model combines the advantages of Molecular Dynamics and Two Temperature Model. We have carried out a direct comparison of the modeling results and experimental data on nano-modification due to a single ps laser pulse at the energy densities significantly exceeding the melting threshold. The experimental data is obtained due to a laser pulse irradiation at the wavelength of 248 nm and duration of 1.6 ps. The mask projection (diffraction grating) creates the sinusoidal intensity distribution on a gold surface with periods of 270 nm, 350 nm, and 500 nm. The experimental data and modeling results have demonstrated a good match subject to complex interrelations between a fast material response to the laser excitation, generation of crystal defects, phase transitions and hydrodynamic motion of matter under condition of strong laser-induced non-equilibrium. The performed work confirms the proposed approach as a powerful tool for revealing the physical mechanisms underlying the process of nanostructuring of metal surfaces. Detailed understanding of the dynamics of these processes gives the possibility for designing the topology of functional surfaces on nano- and micro-scales

Fundamentals of ultrafast laser–material interaction

Abstract

Thermo-kinetic mechanisms for grain boundary structure multiplicity, thermal instability and defect interactions

Grain boundaries (GBs) provide a source and/or a sink for crystal defects and store elastic energy due to the non-uniform atomic bonding structure of the GB core. GB structures are thermodynamically driven to transition to the lowest energy configuration possible; however to date there has been little evidence to explain why specific GB structures have a low energy state. Furthermore, there is little quantitative demonstration of the significance of physical and GB structure characteristics on the GB energy, thermal stability, and the effect of temporary local GB structure transformations on defect interactions. This paper evaluates the defect interactions and structure stability of multiple Σ5(310) GB structures in bi-crystals of pure aluminium, and systematically investigates the features at 0 K to characterise multiple metastable structures. Structure stability is evaluated by utilising unstable vacancy defects to initiate GB transformations, and using nudged elastic band simulations to quantify this with the activation energy. The emission of stable vacancy defects from the ‘stable’ and metastable grain boundaries is also evaluated in the same manner. A detailed analysis of dislocation nucleation at the atomistic scale demonstrates that local transformations of GB structure between stable and metastable intermediates can provide a mechanism to accommodate the generation of crystal defects. Kinetic (time-dependent) effects that compete with energetic driving forces for structural transformations of GBs are shown to cause a significant effect on the activation properties that may exceed the influence of GB potential energy. The results demonstrate that GB structural multiplicity can be associated with the generation and absorption of dislocations and vacancies. This paper demonstrates the suitability of atomistic simulations coupled with nudged elastic band simulations to evaluate fundamental thermodynamic properties of pure FCC metals. Overall, this paper demonstrates an inherent link between the atomic structure and the thermal, energy and structure stability properties of grain boundaries; and reveals the mechanisms for GB-defect interactions involving localised GB structure transformation.

Atomistic simulation study of short pulse laser interactions with a metal target under conditions of spatial confinement by a transparent overlayer

The distinct characteristics of short pulse laser interactions with a metal target under conditions of spatial confinement by a solid transparent overlayer are investigated in a series of atomistic simulations. The simulations are performed with a computational model combining classical molecular dynamics (MD) technique with a continuum description of the laser excitation, electron-phonon equilibration, and electronic heat transfer based on two-temperature model (TTM). Two methods for incorporation of the description of a transparent overlayer into the TTM-MD model are designed and parameterized for Ag-silica system. The material response to the laser energy deposition is studied for a range of laser fluences that, in the absence of the transparent overlayer, covers the regimes of melting and resolidification, photomechanical spallation, and phase explosion of the overheated surface region. In contrast to the irradiation in vacuum, the spatial confinement by the overlayer facilitates generation of sustained high-temperature and high-pressure conditions near the metal-overlayer interface, suppresses the generation of unloading tensile wave, decreases the maximum depth of melting, and prevents the spallation and explosive disintegration of the surface region of the metal target. At high laser fluences, when the laser excitation brings the surface region of the metal target to supercritical conditions, the confinement prevents the expansion and phase decomposition characteristic for the vacuum conditions leading to a gradual cooling of the hot compressed supercritical fluid down to the liquid phase and eventual solidification. The target modification in this case is limited to the generation of crystal defects and the detachment of the metal target from the overlayer.