Crystalline Defects Research Articles

Multinanolayered PA6/Cloisite and PE/PA6/Cloisite composites: Structure, mechanical and barrier properties

Economic and environmental challenges are driving development towards more efficient and lighter materials. Polyethylene (PE) and polyamide (PA6) are among the most used polymers and their assembly in multilayer make them efficient protective materials. The aim of this work is to design new multilayer composite films based on polyethylene and polyamide with high barrier properties. A coextrusion process with layer multiplier elements (LME) made it possible to carry out 100 μm-thick multilayer films containing 5 up to 1025 layers. Loaded PE/PA6 multilayer films were made by incorporating Cloisite particles (organo-modified montmorillonite – C30B) at 5 wt% into the PA6 layers. For comparison PA6 films with and without fillers were also made by using the same coextrusion process. The structural and thermal properties of all multilayer films were correlated with the water and gas barrier properties. A good dispersion of exfoliated C30B in the PA6 phase was observed even for the thinnest confined layers of PA6 in PE/PA6 multilayers (∼90 nm). We showed the complexity of the multinanolayer structures involving interphases as well as the complexity of the transfer mechanisms. The serial model used for predicting permeability highlighted some significant improvements of the gas barrier properties of confined PA6 layers. The barrier effect on all the multilayer films was, however, limited due to the “on-edge” orientation of the crystalline phases and structural defects induced during the coextrusion process. Despite this, the confinement of nanofillers in PA6 multilayers and in PA6 layers of PE/PA6 multilayers allowed to increase the barrier properties of multilayers.

Analysis of Face-Centered Cubic Phase in Additively Manufactured Commercially Pure Ti

Metal additive manufacturing is a developing technique with numerous advantages and challenges to overcome. As with all manufacturing techniques, the specific raw materials and processing parameters used have a profound influence on microstructures and the resulting behavior of materials. It is important to understand the relationship between processing and microstructures of Ti to advance knowledge of Ti-alloys in the additive field. In this study, a face-centered cubic (FCC) phase was found in grade 2 commercially pure titanium specimens, additively manufactured with directed energy deposition in an argon atmosphere. Two scanning speeds (500 and 1000 mm/min) and three scanning patterns (cross-hatched and unidirectional patterns) were investigated. Electron backscatter diffraction and energy-dispersive X-ray spectroscopy were used for microstructural and compositional analysis. Inverse pole figure, phase, and kernel average misorientation (KAM) maps were analyzed in this work. Larger amounts of the FCC phase were found in the unidirectional scanning patterns for the slower scanning speed, while the cross-hatched pattern for both scanning speeds showed a lower amount of FCC. Higher KAM averages were present in the faster scanning speed specimens. According to EDS scans, small amounts of nitrogen were uniformly distributed throughout the specimens, leading to the possibility of interstitial content as a contributing factor for development of the observed FCC phase. However, there is no clear relationship between nitrogen and the FCC phase. The formation of this FCC phase could be connected to high densities of crystalline defects from processing, plastic deformation, or the distribution of interstitials in the AM structure. An unexpected Kurdjumow–Sachs-type orientation relationship between the parent beta phase and FCC phase was found, as 110BCC∥111FCC, 111BCC∥110FCC.

Zn‐doped MnOx nanowires displaying plentiful crystalline defects and tunable small cross-sections for an optimized volcano-type performance towards supercapacitors

MnOx-based nanomaterials are promising large-scale electrochemical energy storage devices due to their high specific capacity, low toxicity, and low cost. However, their slow diffusion kinetics is still challenging, restricting practical applications. Here, a one-pot and straightforward method was reported to produce Zn-doped MnOx nanowires with abundant defects and tunable small cross-sections, exhibiting an outstanding specific capacitance. More specifically, based on a facile hydrothermal strategy, zinc sites could be uniformly dispersed in the α-MnOx nanowires structure as a function of composition (0.3, 2.1, 4.3, and 7.6 wt.% Zn). Such a process avoided the formation of different crystalline phases during the synthesis. The reproducible method afforded uniform nanowires, in which the size of cross-sections decreased with the increase of Zn composition. Surprisingly, we found a volcano-type relationship between the storage performance and the Zn loading. In this case, we demonstrated that the highest performance material could be achieved by incorporating 2.1 wt.% Zn, exhibiting a remarkable specific capacitance of 1082.2 F.g−1 at a charge/discharge current density of 1.0 A g−1 in a 2.0 mol L−1 KOH electrolyte. The optimized material also afforded improved results for hybrid supercapacitors. Thus, the results presented herein shed new insights into preparing defective and controlled nanomaterials by a simple one-step method for energy storage applications.

The nature of crystallographic defects in noncrystalline tubular network block copolymers

Defects are symmetry breaking features within a crystal. They can be created during growth as well as by applied mechanical forces. We address point, line and surface defects in block copolymer crystals, concentrating on the structure of defects in the tubular network double gyroid and double diamond phases. Experimental results using 3D slice and view scanning electron microscopic tomographic imaging for many types of defects are presented and the nature of the structural details and symmetries are described. Often defects are considered detrimental to the properties and performance of the material, but if the mesoscale defects in 3D periodic block copolymers can be controlled, they can be utilized to achieve various advantageous such as new optical functionalities.

Structure refinement, Raman vibration, impedance spectra and microwave dielectric properties of MgZrNb2-x(Ge1/2W1/2)xO8 (0.02≤x≤0.08) ceramics with the high quality factor

The prosperous development of 5G technology requires the development of new high-performance microwave dielectric ceramics. MgZrNb2-x(Ge1/2W1/2)xO8 (MZNGW) (0.02≤ x ≤ 0.08) ceramics were synthesized by the solid-state reaction with the high quality factor. The connection between the microstructure and microwave dielectric properties of MZNGW ceramics was systematically analyzed. Crystal structure refinement showed that MZNGW ceramics with monoclinic wolframite structure were synthesized in all samples. The sintering behavior and surface morphology indicate that doping of (Ge1/2W1/2)5+ can improve the densification and promote the grain growth. The effect of (Ge1/2W1/2)5+ doping on the phonon vibration can be obtained from Raman spectra, and the shift of Raman vibrational mode at 840 cm−1 and the change of half-height width have a great influence on the dielectric constant and quality factor. XPS spectra and AC impedance spectra are analyzed to show the influence of the crystalline defects on the macroscopic properties of the interlayer. The MgZrNb1-x(Ge1/2W1/2)xO8 (x = 0.04) ceramic exhibits excellent microwave dielectric performance sintered at 1420 °C for 4 h: εr = 27.1, Qf = 94,450 GHz, τf = −41.65 ppm/°C, with great potential for applications in modern communications.

Effect of step-flow modulation on the large-size single crystal diamond through mosaic growth

In this paper, large-size single crystal diamond is grown by microwave plasma chemical vapor deposition using mosaic technique. The effects of the step-flow modulation on the surface morphology and crystal quality of epitaxial single crystal diamond layer are systematically investigated. It demonstrates that the two adjacent crystals can be merged into a single crystal layer with good surface morphology and uniform quality when their step-flow orientations are similar. Otherwise, over-lap is observed because of the overgrowth from one seed to another, resulting in stress concentration and a large number of crystalline defects at the mosaic boundaries. Finally, we demonstrate that the step-flow modulation method facilitates the mosaic growth of inch-scale single-crystal diamond with 10 CVD seeds arranged in a T-shape.

Elucidating influences of defects and thermal treatments on CO2 capture of a Zr-based metal–organic framework

Carbon capture and storage (CCS) technology is currently an essential response to the global warming problem caused by excessive CO2 emissions. Efficient and reproducible adsorbents for flue gas treatment play an important role in CCS technology, and metal–organic frameworks (MOFs) are considered to be ideal candidates by virtue of their designable CO2 sorption sites. However, carbon capture performance evaluation and reproducibility of MOFs still hinder their application promotion in industrial production. In this work, an extended UiO-66-type MOF based on 1,4-naphthalenedicarboxylate, was successfully synthesized in both a near defect-free form (UiO-66N) and a defect-rich form (DUiO-66N), for exploring the influence of crystalline defects and thermal treatments on carbon capture performance. Although powder X-ray diffraction showed that UiO-66N and DUiO-66N possessed the same crystalline phase, transmission electron microscopy, thermalgravimetric analyse and gas/dye sorption confirmed the presence of crystalline defects and the variation of porosity in DUiO-66N. CO2 sorption isotherms and flue gas breakthrough experiments revealed the defect-induced improved carbon capture performance, which was also supported by density functional theory. Meanwhile, the metastability of defects required low thermal treatment temperatures for activation and regeneration thus maintaining the superior carbon capture performance. These findings suggested that in reproducing and evaluating the carbon capture performance of MOFs, it cannot rely only on the global crystalline phase judgment, but needs to identify the local fine structure as well as optimize activation and regeneration conditions.

Engineering the structural and electrical interplay of nanostructured Au resistive switching networks by controlling the forming process

Networks of random-assembled gold clusters produced in the gas phase show resistive switching (RS) activity at room temperature and they are suitable for the fabrication of devices for neuromorphic data processing and classification. Fully connected cluster-assembled nanostructured Au films are characterized by a granular structure rich of interfaces, grain boundaries and crystalline defects. Here we report a systematic characterization of the electroforming process of the cluster-assembled films demonstrating how this process affects the interplay between the nano- and mesoscale film structure and the neuromorphic characteristics of the resistive switching activity. The understanding and the control of the influence of the resistive switching forming process on the organization of specific structures at different scales of the cluster-assembled films, provide the possibility to engineer random-assembled neuromorphic architectures for data processing task.

Superconducting properties and vortex pinning in intermetallic BaBi3 single crystals: A magnetization study

Hysteresis and magnetic relaxation measurements were performed on single crystals of BaBi3, which is an intermetallic compound exhibiting superconductivity with a critical temperature (Tc) of 5.9 K. The London penetration depth (λ) was determined to be 130 nm, and the coherence length (ξ) was estimated to be 13 nm. The critical current density (Jc) was found remarkably low, measuring 20,000 A/cm2 under self-field conditions at 1.8 K. Analysis of the pinning forces suggests vortex pinning by crystalline defects associated with volume Δk (variations in the Ginzburg-Landau parameter). The relaxation rate follows the Anderson-Kim model, and the pinning energies range from 1600 K at 0.02 T to 500 K at 0.5 T. Our study aims to advance our understanding of the connection between intrinsic superconducting properties and vortex behavior in intermetallic materials characterized by low thermal fluctuations.

Laser powder bed fused 304L steel shot-peened with various ceramic shot sizes: Surface/subsurface characteristics, tensile behavior, and fatigue behavior

Shot peening is an efficient post-processing technique for eliminating surface manufacturing defects, inducing compressive residual stress, and improving the mechanical properties of laser powder bed fused (L-PBFed) metallic materials. With a series of microstructural characterizations, this work comprehensively evaluated the influence of ceramic shot size on the surface characteristics, subsurface characteristics, and mechanical properties, especially fatigue performance, of L-PBF manufactured 304L austenitic stainless steel (SS). The mechanical testing process was in situ observed using an infrared thermal camera, and the tensile-fractured and fatigue-fractured microstructures were systematically examined, aiming to explore the life improvement mechanisms caused by different ceramic shot sizes. The results revealed that when compared to small-sized AZB 100 shots, the large-sized AZB 300 shots could result in higher surface roughness, larger thickness reduction, more apparent surface gradient structure, higher strength, and longer fatigue lifetimes. The strength improvement could be associated with the size reduction of L-PBF induced subsurface defects, the grain refinement at the surface layer, and the α'-martensitic transformation during tensile deformation. The life improvement could be primarily attributed to the subsurface defect strengthening, which resulted in the fatigue crack initiation transition from subsurface defects to surface defects. During the fatigue process, the energy dissipation originating from the core materials dominated the thermal equilibrium temperature, whereas the density of micro-defects (crystalline defects) at the surface layer dominated the crack tip temperature. These findings provide a basic understanding of how to advance the shot peening process for L-PBFed materials.

Improvement of charge carrier lifetime in heat exchange method multicrystalline silicon wafers by extended phosphorous gettering process

External phosphorous diffusion gettering were applied using homogenous and extended schemes on multicrystalline silicon (Mc-Si) wafers obtained from solar grade (SOG) silicon feedstock by the heat exchange method (HEM) growth technique. X-ray fluorescence (XRF) characterization shows the presence of transition metals like Chromium (Cr), manganese (Mn) and iron (Fe) in the analyzed as-cut Mc-Si substrates with a predominance of Mn and Fe elements. Before and after gettering process, we have observed that the Cr atoms concentration drop from 4.1015 at.cm-3 in the as-cut Mc-Si samples to 2.5 1015 at.cm-3 with homogeneous gettering and to 3.1014 at.cm-3 in the wafer undergoes extended gettering. The quasi-steady-state photo conductance (QSSPC) technique is used to characterize the minority charge carrier’s lifetime tn before and after gettering process. It was found that the response of Mc-Si wafers is better (form point of view of lifetime improvement) to the extended process but in some regions it is less effective and the homogenous process give the best amelioration due probably to the spatial distribution of crystalline defects and metallic precipitates densities. With tn initial values before gettering in the range of 2.5-8 usec we have measured lifetime values in the range of 15 to 37 usec with extended process and from 10 to 30 µsec with the homogenous one which ensure cell efficiencies in the range of 15 to 16%.

Imaging of atomic stress at grain boundaries based on machine learning

The mechanical behaviors of crystalline materials, in particular the atomic scale deformation and failure processes, are strongly influenced by the local atomic stress near crystalline defects such as vacancies, dislocations and grain boundaries (GBs). Modern electron microscopy techniques have achieved unprecedented capabilities to image the internal microstructure of crystalline materials with atomic resolution. In comparison, our ability to map the corresponding atomic stress field, especially at grain boundaries with complex atomic structures, remains lagging behind due to the lack of direct experimental methods for stress measurement. Here, we propose a machine learning-based framework to realize atomic structure-stress (Atom-S2) mapping based on in situ transmission electron microscopy images. We demonstrate that, with optimized anti-noise performance and generalization ability, the Atom-S2 framework enables quantitative mapping of atomic stress in symmetrical tilt GBs, twin boundaries (TBs) as well as general GBs with changing curvature in crystalline metals. Moreover, the Atom-S2 can help understand, interpret and predict grain boundary stress evolution and plastic deformation mechanisms based on high-resolution transmission electron microscopy images, which provides a powerful tool to study atomic scale deformation behaviors and holds promises for accelerating materials design through defect engineering.

Improved sputtering method to deposit high conducting doped ZnO films without substrate heating

Magnetron sputtering deposition with Zn supply was utilized to deposit Ga-doped ZnO (GZO) films to minimize acceptor-like crystalline defects. This deposition technique significantly increased the carrier concentration of GZO films. In addition, the impact of partial oxygen pressure on the deposition atmosphere on carrier concentration was remarkably reduced. As a result, the resistivity of the films decreased to as low as 4 × 10−4 Ωcm without the need for intentional substrate heating. Consequently, the deposition with Zn supply shows great potential for producing ZnO-based transparent conducting films with practically low resistivity on polymer substrates that have lower heat tolerance.

Study of the Structural Properties of NiCl2:Al2O3 Thin Film Prepared by Chemical Thermal Spraying Technique

Background: The structural properties of films are studied by several techniques, and X-ray diffraction (XRD) is one of the most reliable methods that were adopted in this research, so will explain it in some detail, in addition to assays (SEM ) that give information on surface morphology. Materials and Methods: The thermochemical spraying technique was used to prepare the thin films. Results: The results showed that increasing the temperature led to a decrease in the average particle size, in contrast to the doping process. Conclusion: The reason for the decrease in particle size is due to the increase in the Full Width at Half Maximum (FWHM) in addition to an increase in the crystallization of the thin films, and also the membrane becomes more regular and crystalline defects decrease and increase.

Antioxidant Activity of Ablated Cerium Dioxide Nanoparticles in an Oxidative Photocatalytic Reaction

Purpose of the study. Study and comparison of the antioxidant properties of ablated cerium dioxide nanoparticles in the oxidative photocatalytic degradation of methylene blue ablated from imported and laboratory targets.Methods. By pressing cerium dioxide powder and annealing the pressed target, laboratory targets were obtained, which were subjected to the laser ablation process. Atomic force microscopy was used to characterize cerium dioxide nanoparticles. The spectrophotometric method was used to study the antioxidant properties of cerium dioxide nanoparticles. The antioxidant activity of ablated nanoparticles obtained from two targets in an oxidative photocatalytic reaction has been studied and compared. Cerium dioxide nanoparticles with high antioxidant activity were obtained by laser ablation.Results. Using atomic force microscopy, the average limiting sizes of non-centrifuged and centrifuged samples at a speed of 1000 rpm of ablated cerium dioxide nanoparticles were established. It was found that the elemental composition of the cerium dioxide powder, from which the laboratory target was pressed, and the elemental composition of the imported target are the same, and the percentage of impurities in them is within the limits acceptable for the laser ablation process. The antioxidant activity of cerium dioxide nanoparticles ablated from laboratory and imported targets was compared. The data obtained in the course of the study indicate that cerium dioxide nanoparticles obtained from a laboratory target exhibit the highest antioxidant activity.Conclusion. Cerium dioxide nanoparticles subjected to laser ablation from a laboratory target are nanomaterials that are antioxidants that inactivate reactive oxygen species in a photocatalytic reaction. The antioxidant activity of cerium dioxide nanoparticles obtained from a laboratory target is not lower, but higher than that of nanoparticles obtained from an imported target. These properties of cerium dioxide nanoparticles are due to the presence of crystalline defects such as oxygen vacancies on their surface.

Preparing metallic bulk samples for transmission electron microscopy analysis via laser ablation in an acidic liquid

The laser ablation process has been presented as a state-of-the-art and robust method for eliminating surface layers of metallic bulk materials on the micro/nanoscale with considerable accuracy and speed. These capabilities make it an ideal instrument for the primary step of metallic bulk sample preparation for transmission electron microscopy (TEM) analysis with minimal damage to the crystal structure of the sample. This work prepared a pure aluminum plate by fiber laser scanning immersed in a 5 % perchloric acid and 95 % ethanol (by volume) solution. The laser ablation in an acidic liquid condition was used in the chemical etching process, to prevent oxidation, minimize the heat-affected region, and induce crystalline defects. For this purpose, a continuous wave fiber laser with a power of 100 W, a wavelength of 1064 nm, and a focusing distance of 305 mm was applied. The TEM analysis for the as-prepared sample by the laser ablation process was compared to the standard jet electro-polishing method in the same solution. The results showed that crystal structure variations such as grain size and lattice defects did not occur in the aluminum sample due to the thermal effects of the laser ablation process. The average size of the grains and zone axis were about 600–800 nm and z = [011], respectively, in as-prepared samples by both methods; In addition, very few dislocations were observed in the grain boundaries and inside the grains. Therefore, based on the obtained results, laser ablation could be considered an eco-friendly, comfortable, fast, and cost-effective method with a small volume of chemicals used, compared to the standard jet electro-polishing method for the TEM preparation of the metallic bulk samples.

Semiconductor Wafer Bonding for Solar Cell Applications: A Review

Wafer bonding is a highly effective technique for integrating dissimilar semiconductor materials while suppressing the generation of crystalline defects that commonly occur during heteroepitaxial growth. This method is successfully applied to produce efficient solar cells, making it an important area of research for photovoltaic devices. In this article, a comprehensive review of semiconductor wafer‐bonding technologies is provided, focusing on their applications in solar cells. Beginning with an explanation of the thermodynamics of wafer bonding relative to heteroepitaxy, the functionalities and advantages of semiconductor wafer bonding are discussed. An overview of the history and recent developments in high‐efficiency multijunction solar cells using wafer bonding is also provided. Bonded solar cells made of various semiconductor materials are reviewed and various types of wafer‐bonding methods, including direct bonding and interlayer‐mediated bonding, are described. Additionally, other technologies that utilize wafer bonding, such as flexible cells, thin‐film transfer, and wafer reuse techniques, are covered.

Thermal oxidation of MoS2 into defective crystalline MoO3 with enhanced Li-ion storage kinetics

Thermal oxidation in air of molybdenum disulfide (MoS2) into layer structured molybdenum trioxide (α-MoO3) is investigated using a combination of thermal analysis, electron microscopy, Raman, X-ray diffraction and photoelectron spectroscopy. The phase evolutions occurred during the thermal process is characterized by the surface oxidation of MoS2, followed by the bulk oxidation to form α-MoO3 and the formation of Mo17O47 at higher temperatures. The single-phase MoO3 formed at optimum temperature condition is found to possess crystalline defects and considerably greater values of Li-ion storage cycling and rate performances in comparison with samples prepared at alternative temperatures and also the initial MoS2. This sample (P-MoO3-820) exhibits a charge capacity of 628 mA h g−1 after 250 cycles (100 mA g−1) with a Li+ diffusion coefficient of 2.3 × 10-13 cm2 s−1, substantially greater than that of initial MoS2 (8.1 ×10−16 cm2 s−1). The electrochemical performance of P-MoO3-820 in full-cell configuration against a commercial LiFePO4 cathode is evaluated and a specific capacity of 100 mAh g−1 after 500 cycles is recorded. This article, for the first time, discusses the thermal oxidation in air of MoS2 as a simple and relatively clean approach to fabricate defective crystalline MoO3 with enhanced Li-ion storage kinetics.

Optimizing antimony trisulfide thin films: enhanced structural and optoelectronic properties via post-annealing in sulfur atmosphere

Antimony trisulfide (Sb2S3) is a promising material for photoabsorption due to its high absorption coefficient, low toxicity, and abundance in nature. However, various stoichiometric and crystalline defects have limited its practical applications. Herein, highly crystalline Sb2S3 thin films are fabricated via thermal evaporation and subsequent annealing in a sulfur atmosphere at different temperatures. The analyses of X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and optical properties reveal highly crystalline Sb2S3 thin films. The films showed reduced stoichiometric and crystal defects, while also displyaing enhanced optical and morphological properties. The improvement in the physical properties of the Sb2S3 thin films is attributed to the filling of sulfur deficiencies by extra sulfur vapors present during the thermal annealing process. Moreover, annealing the obtained Sb2S3 samples at different temperatures (ranging from 250 °C to 300 °C) reveals that the Sb2S3 films exhibit improved physical properties at 300 °C, which is considered to be the optimal annealing temperature. Our findings open up a pathway for the fabrication of highly crystalline Sb2S3 thin films, which could lead to the development of efficient optoelectronic devices.

Two-Dimensional Pb Square Nets from Bulk (RO)nPb (R = Rare Earth Metals, n = 1,2).

All two-dimensional (2D) materials of group IV elements from Si to Pb are stabilized by carrier doping and interface bonding from substrates except graphene which can be free-standing. The involvement of strong hybrid of bonds, adsorption of exotic atomic species, and the high concentration of crystalline defects are often unavoidable, complicating the measurement of the intrinsic properties. In this work, we report the discovery of seven kinds of hitherto unreported bulk compounds (RO)nPb (R = rare earth metals, n = 1,2), which consist of quasi-2D Pb square nets that are spatially and electronically detached from the [RO]δ+ blocking layers. The band structures of these compounds near Fermi levels are relatively clean and dominantly contributed by Pb, resembling the electron-doped free-standing Pb monolayer. The R2O2Pb compounds are metallic at ambient pressure and become superconductors under high pressures with much enhanced critical fields. In particular, Gd2O2Pb (9.1 μB/Gd) exhibits an interesting bulk response of lattice distortion in conjunction with the emergence of superconductivity and magnetic anomalies at a critical pressure of 10 GPa. Our findings reveal the unexpected facets of 2D Pb sheets that are considerably different from their bulk counterparts and provide an alternative route for exploring 2D properties in bulk materials.