Distribution Of Crystalline Phases Research Articles

The Key Role of Hole Transport Layer in Boosting Performance of Two‐Dimensional Perovskite Solar Cells

Although currently in the nascent stages of research and development, two‐dimensional perovskite solar cells have showcased remarkable promise as the robust and efficient solar cell technology. Anticipated progressions and refinements in this domain are poised to establish two‐dimensional perovskite cells as instrumental catalysts in shaping the trajectory of renewable energy, heralding transformative breakthroughs. The hole transport layer (HTL) plays an irreplaceable role in the charge carriers’ transport and interface effects in two‐dimensional perovskite devices. This review starts with the structural characteristics of two‐dimensional perovskite solar cells. The influence of the intrinsic characteristics of the perovskite active layer itself and the interaction of the perovskite/transport layer contact interface are analyzed. This discussion delves into the impact of intrinsic quantum confinement and the dielectric effect within the two‐dimensional perovskite structure on photovoltaic conversion efficiency. It also explores the energy level alignment between the clathrate active layer and the transport layer. The significance of the HTL is emphasized, particularly regarding crystalline control, phase distribution, and interface passivation. Additionally, the crucial role of efficient carrier transport between the active layer and the transport layer is thoroughly examined.

Resolving conjugated polymer film morphology with polarised transmission and time-resolved emission microscopy

The alignment of chromophores plays a crucial role in determining the optoelectronic properties of materials. Such alignment can make interpretation of fluorescence anisotropy microscopy (FAM) images somewhat ambiguous. The time-resolved emission behaviour can also influence the fluorescence anisotropy. This is particularly the case when probing excitation energy migration between chromophores in a condensed phase. Ideally information concerning the chromophoric alignment, emission decay kinetics and fluorescence anisotropy can be recorded and correlated. We report on the use of polarised transmission imaging (PTI) coupled with both steady-state and time-resolved FAM to enable accurate identification of chromophoric alignment and morphology in thin films of a conjugated polydiarylfluorene. We show that the combination of these three imaging modes presents a comprehensive methodology for investigating the alignment and morphology of chromophores in thin films, particularly for accurately mapping the distribution of amorphous and crystalline phases within the thin films, offering valuable insights for the design and optimization of materials with enhanced optoelectronic performance.

Spectroscopic evaluation of nitrogen glow discharge for the surface nitriding of Ti-6Al-4V alloy

The study investigates the spectral characteristics of a DC glow discharge generated in a parallel electrode configuration for nitriding the Ti-6Al-4V alloy to enhance its surface properties. At first, optical emission spectroscopy (OES) was used to optimize the glow discharge for a certain nitrogen fill pressure and discharge power. The Ti-6Al-4V alloy is then subjected to plasma treatment in an optimized N2-discharge environment. The treated samples' microstructures, surface morphology, elemental composition, and surface roughness are all determined by several material characterization techniques, including XRD, SEM, EDX, and AFM. The Ti-alloy's crystalline phase distribution affects the alloy's physical and chemical characteristics, which determine its suitability for various applications in aerospace and medical implants. A phase shift from Ti(101)α to Ti(110)β is observed owing to the progressive increase in nitrogen interstitials in Ti sites, which promotes the phase transition. The EDX results show that the amount of nitrogen in the spectrum increases, demonstrating that nitrogen has successfully been incorporated into the surfaces of alloys. The surface morphology of the treated samples has improved with longer treatment times, as seen by SEM pictures of samples that have received plasma treatment. Finally, the comparison of the samples' AFM topological measurements and textures at 5, 10, and 15 h demonstrates the importance of treatment time on the development of the Ti-6Al-4V surface roughness and microstructure.

Reproducibility of physico-chemical properties in brakes emissions generated at the dynamometric bench

Reproducible generation, collection and physico-chemical characterization of brakes emissions are necessary when comparing particulates generated by different friction couples, brake designs or driving conditions. Furthermore, they are pivotal to provide universally reliable chemical information for source apportionment studies as well as for toxicological investigations and environmental assessments. Non-exhaust particulates generated by brakes are nowadays commonly collected at suitably designed variable inertia dynamometer benches, during selected braking test cycles in controlled conditions to avoid other contributions from the environment. In spite of being simplified models of a single real car semi-axis corner, dynamometric benches for brakes emissions collection still remain elaborate mechanical devices used for testing complex materials. Therefore, if the tribological interaction is not kept constant over different tests, significantly different local forces and temperatures might be expected at the tribological interface. This can eventually result in the generation of particulates with different granulometry and chemical composition, even if originated by the same braking device components. At this regard, the work here presented explores for the first time the capability of a brake dynamometer bench dedicated to emission tests to generate reproducible particulates. In particular, the assessment of the intrabench reproducibility over an extended period of time and number of tests is discussed. Specifically, the variability of physico-chemical properties such as particle size distribution, elemental composition and crystalline phase distribution is evaluated. In detail, it is observed that the elemental concentration of main constituents such as Iron and Oxygen are statistically equivalent during a set of ten tests, even at strict confidence level (α = 0.05). In addition, when statistical differences are observed in elemental concentration of secondary and minor constituents, their variability typically remains limited below the 10 % of the corresponding figure of merit. Similar findings are also observed when assessing the phase composition of main constituents compounds, such as Iron oxides, as well as the particle size distribution profiles. Conversely, higher relative variabilities up to 25 % are registered when assessing the phase composition of secondary and minor phases. The reported results are meant to provide a first critical assessment on the variability of both the size distribution and the chemical composition of the emissions generated by brakes in the laboratory environment typically used for their generation, measurements and collection.

Cold‐cap structure in a slurry‐fed electric melter

AbstractAs glass batch is charged into an electric melter, a cold cap forms on the glass melt surface. Heat transfer to the cold cap from the molten glass below and the melter atmosphere above determines the melting rate. A mathematical model of the cold cap and the experimental kinetic data of the feed‐to‐glass conversion that were collected for several simulated low‐activity and high‐level waste melter feeds allowed us to develop relationships between the internal structure of the cold cap, its properties, its thickness, and the internal heat transfer. This contribution shows the distribution of major crystalline phases and the cumulative evolution of gases within the cold cap. It also examines the temperature, conversion degree, and heating rate the melter feed is experiencing during the passage through the cold cap and their effects on the cold‐cap bottom temperature and morphology, which are important for the computational fluid dynamics simulations of melters.

Lotus-root-like titanium dioxide photocatalyst with a hierarchical micro-/meso-/macroporous structure

Titanium dioxide agglomerate with a hierarchical micro-/meso-/macroporous structure was synthesized by a very simple method using only titanium alkoxide and water as raw materials. The microscopic morphology of the agglomerate looked like a lotus-root including cylindrical macropores with sizes of 1–10 μm in diameter penetrating into the agglomerate. The agglomerate was composed of TiO2 nanoparticles that form micropores smaller than 1 nm and mesopores smaller than 10 nm. The agglomerate was heat-treated at 300–700oC for 1 h to modify its crystalline phase, crystallite size, and pore size distribution. Anatase-type agglomerates with a micro-/meso-/macroporous structure having specific surface areas of 35–405 m2/g showed high humidity buffering performance and high photocatalytic activity. Both properties are equal to or higher than each of the commercial products. Furthermore, they showed high hydrophilicity with a water contact angle below 20 degrees even before UV light irradiation.

High-Frequency Ultrasonic Spectroscopy of Structure Gradients in Injection-Molded PEEK Using a Focusing Transducer.

For high-performance thermoplastic materials, material behavior results from the degree of crystallization and the distribution of crystalline phases. Due to the less stiff amorphous and the stiffer and anisotropic crystalline phases, the microstructural properties are inhomogeneous. Thus, imaging of the microstructure is an important tool to characterize the process-induced morphology and the resulting properties. Using focusing ultrasonic transducers with high frequency (25 MHz nominal center frequency) enables the imaging of specimens with high lateral resolution, while wave propagation is related to the elastic modulus, density and damping of the medium. The present work shows experimental results of high-frequency ultrasonic spectroscopy (HF-US) applied to injection-molded polyether-ether-ketone (PEEK) tensile specimens with different process-related morphologies. This work presents different analysis procedures, e.g., backwall echo, time of flight and Fourier-transformed time signals, facilitating the mapping of gradual mechanical properties and assigning them to different crystalline content and morphological zones.

Nonuniform Distribution of Crystalline Phases and Grain Sizes in the Surface Layers of WC Ceramics Produced by Spark Plasma Sintering

The research results conducted on binderless tungsten carbide (WC) ceramics obtained by spark plasma sintering (SPS) of WC powders with different average particle sizes (95, 800, 3000 nm) are presented. Nonuniform distribution of crystalline phases and microstructure of the WC ceramics was studied using layer-by-layer X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Surface layers of the WC-based ceramics are characterized by nonuniform distribution of W2C crystalline phase and grain sizes, including the appearance of abnormally large grains. Thickness of the nonuniform layer was at least 50 μm. The effect under study is associated with an intense carbon diffusion from graphite foil. On the one hand, this contributed to a decrease in the intensity of W2C phase particle formation, which is transformed into α-WC phase due to the carbon. On the other hand, it caused abnormal grain growth in the layer where the carbon diffused. The obtained value of the carbon diffusion depth (50 μm) exceeds the values known from the literature (up to 1 μm in the case of volume diffusion even at temperature of 2370 °C and exposure time of ~60 h). The use of boron nitride (BN) as a protective coating on graphite mold parts did not prevent the formation of nonuniform layer on the ceramic surface.

CO2 capture based on Al2O3 ceramic membrane with hydrophobic modification

In this paper, Al2O3 ceramic membrane is modified to hydrophobicity by grafting 1 H,1 H,2 H,2 H-perfluorodecyltriethoxysilane. And its properties are characterized in detail. CO2 capture performance of ceramic membrane is investigated by experiments. Results show that wetting resistance after modification is significantly improved, and contact angle increases from the initial 49.8–130.9°. However, hydrophobic modification has no significant effect on the crystalline phase, surface morphology and pore size distribution of the ceramic membrane. With ethanolamine (MEA) as absorbent, CO2 mass transfer rate and capture efficiency using modified hydrophobic ceramic membrane are 46.6 × 10−3 mol/(m2·s) and 98.0%, showing significantly increase compared to the original membrane. After 72 h immersion in MEA solution, quality of ceramic membrane does not change significantly. And there is almost no change in average pore size. We believe this study will provide a reference for the industrial application for CO2 capture by gas-liquid membrane contactor with ceramic membrane.

Deep-learning approach for predicting crystalline phase distribution of femtosecond laser-processed silicon

In this study, two deep-learning models are presented to predict the crystalline phases of femtosecond laser-processed silicon. To obtain the datasets, single-crystal silicon was processed by a femtosecond laser using 49 different combinations of laser fluence and scanning speed, and for each specimen, Raman spectra were measured at 22,500 locations inside a square domain. The first model was trained to classify the Raman spectra of silicon into six silicon phases. By applying the model to the entire surface of a silicon specimen in batches, the silicon phase distribution was visualized in RGB color values, with each color representing a particular silicon phase. Using the classification results of the 49 specimens obtained by the first model, the second model was developed to predict the silicon phase distribution image from the inputs of the laser fluence and scanning speed. The average prediction accuracy of the second model was 86.60%.

Effect of Nd2O3 on microstructure, corrosion and wear properties of laser cladding Zr-based amorphous composite coatings on AZ91D magnesium alloy

The preparation of amorphous matrix composite coatings by laser cladding is a applicable approach to improve the surface properties of Mg and Mg alloys. Rare earth elements significantly affect the corrosion and wear resistance of the coatings by influencing the quantity, morphology and distribution of crystalline phases. In the presented work, Zr55Cu30Al10Ni5 + x wt% Nd2O3 (x = 0, 0.5, 1, 1.5, 2, 3) composite coatings were prepared by laser cladding on the AZ91D Mg alloy. The coatings were composed of dendrites, cellular grains, Nd enriched spherical structure and amorphous matrix. Appropriate Nd2O3 addition can refine the size of crystalline microstructure, purify oxygen impurities and increase amorphous content of the coatings, but excessive addition of Nd2O3 (2–3 wt%) causes aggregation and abnormal growth of some crystalline phases and deteriorates the glass forming ability of the coatings. Corrosion resistance of the coating with 1.5 wt% Nd2O3 is the most excellent relying on the highest amorphous and the lowest crystalline phases contents in this coating. Wear resistance of the coatings is all greatly improved compared with the Mg substrate, however that are no linearly related to the hardness and do not follow completely the Archard's wear equation.

Femtosecond Laser Fabrication of Anisotropic Structures in Phosphorus- and Boron-Doped Amorphous Silicon Films.

Femtosecond laser-modified amorphous silicon (a-Si) films with optical and electrical anisotropy have perspective polarization-sensitive applications in optics, photovoltaics, and sensors. We demonstrate the formation of one-dimensional femtosecond laser-induced periodic surface structures (LIPSS) on the surface of phosphorus- (n-a-Si) and boron-doped (p-a-Si) amorphous silicon films. The LIPSS are orthogonal to the laser polarization, and their period decreases from 1.1 ± 0.1 µm to 0.84 ± 0.07 µm for p-a-Si and from 1.06 ± 0.03 to 0.98 ± 0.01 for n-a-Si when the number of laser pulses per unit area increases from 30 to 120. Raman spectra analysis indicates nonuniform nanocrystallization of the irradiated films, with the nanocrystalline Si phase volume fraction decreasing with depth from ~80 to ~40% for p-a-Si and from ~20 to ~10% for n-a-Si. LIPSS' depolarizing effect, excessive ablation of the film between LIPSS ridges, as well as anisotropic crystalline phase distribution within the film lead to the emergence of conductivity anisotropy of up to 1 order for irradiated films. Current-voltage characteristic nonlinearity observed for modified p-a-Si samples may be associated with the presence of both the crystalline and amorphous phases, resulting in the formation of potential barriers for the in-plane carrier transport and Schottky barriers at the electric contacts.

Effects of Chitosan on Loading and Releasing for Doxorubicin Loaded Porous Hydroxyapatite-Gelatin Composite Microspheres.

Porous hydroxyapatite–gelatin (Hap–Gel) composite microspheres derived by wet chemical methods were used as carriers of doxorubicin (DOX) coupled with chitosan (Chi) for treating cancers. Through X-ray diffraction, specific surface area porosimetry, chemisorption analysis and inductively coupled plasma mass spectrometry, the crystalline phase, composition, morphology, and pore distribution of HAp–Gel microspheres were all characterized. HAp nanosized crystals and Gel polymers form porous microspheres after blending and exhibit a specific surface area of 158.64 m2/g, pore sizes from 3 to 150 nm, and pore volumes of 0.4915 cm3/g. These characteristics are suitable for carriers of DOX. Furthermore, by the addition of chitosan during drug loading, its drug-entrapment efficiency increases from 70% to 99% and the release duration increases from a 100% burst within a day to only 45% over half a year since the pores in the composite microspheres provide a shielding effect throughout the degradation period of the chitosan. According to the MTT tests, cell viability of DOX–Chi/HAp–Gel is 57.64% on day 5, similar to the result treated with DOX only. It is concluded that under the protection of pores in the microspheres, the chitosan abundant of hydroxyls combining HAp–Gel and DOX by forming hydrogen bonds indeed enhances the entrapment efficiency, prolongs the releasing period and maintains DOX’s ability to perform medicine functions unaffected after loading.

Moderation of thermoplastic composite crystallinity and mechanical properties through in-situ manufacturing and post-manufacturing tempering: Part 2 – Morphological characterisation

The piecewise nature of Automated Fibre Placement for thermoplastic composite materials can lead to significant variations in polymer characteristics over the full part volume, in large part owing to differences in cooling rate from melt and the number of high-temperature cycles to which a given point is exposed. In this work, ion etching is used to remove amorphous material from laminate samples and expose the crystalline structure in the matrix. This structure is then assessed using electron microscopy for all material layers, providing insight into the distribution of amorphous and crystalline phases. This investigation assesses laminates produced using unheated as well as heated (145 ℃ and 220 ℃) tooling surfaces to determine the impact on part crystallinity. Samples are also exposed to post-manufacturing tempering to evaluate its ability to alter part morphology without expensive autoclave or thermo-forming operations. The results reveal significant variation in the morphology of a single sample, with an increased tooling temperature acting to promote crystallinity and homogeneity within the part. Furthermore, a significant difference between the morphology of material layers and the boundary zone between adjacent layers is observed, providing insight into previously obtained mechanical properties.

Effect of nano ZrB2 particles on physical, mechanical and corrosion properties of Al6061 metal-matrix nano composites through stir casting route

The present study investigated the microstructure, mechanical and corrosion behaviour of Al6061 alloy reinforced with nano zirconium diboride (ZrB2) particles. The stir casting route is carried out to fabricate the Al6061 metal matrix nanocomposites (AMMNCs) by varying 0 to 2 Wt% of ZrB2 nanoparticles. X-ray Diffraction (XRD)was used to study the crystalline size and phase distribution of AMMNCs. Scanning electron microscope (SEM) analysis reveals the uniform dispersion of ZrB2 nano particulates in AMMNCs. Ultimate tensile strength and yield strength, hardness of the AMMNCs were increased by 33.58%, 27.54%, and 40.57%, respectively, with the addition of ZrB2 nano particulates, while the elongation decreased to 46.03%. with the increase in ZrB2 Wt%. The corrosion rate of AMMNCs (2 Wt% ZrB2) decreased by 86% compared to Al6061 alloy. Fracture analysis of the samples showed that the fracture behaviour of Al6061 matrix alloy changed from ductile intergranular fracture to cleavage. The results show that the developed nanocomposite enhances mechanical properties and corrosion resistance with an increase in Wt% of reinforcement.

Influence of organic acids on the phases and physical characteristics of titanium dioxide synthesized by sol–gel for air depollution through heterogeneous photocatalysis

AbstractBACKGROUNDAir pollution in big cities is becoming a global problem due to its negative consequences on human health and the ecosystem. Currently, some materials available promise successful gases pollutants removal, by reacting with them through photocatalysis when sunlight irradiates them. The most studied and applied material is TiO2; due to its chemical stability and availability, it is widely incorporated into cements, bricks, coatings, etc.RESULTSIn this study, powders of titanium dioxide were synthesized through the sol–gel method using tetraisopropoxide with and without organic acids. Their photocatalytic activity was determined by the colorimetric method, following the standard UNI‐11259, and by the NO abatement test using the international standard ISO‐22197‐1. The results of the colorimetric test indicate that all the samples are photoactive according to the criteria stablished in the standard. Additionally, a similar photocatalytic performance was evidenced in the NO abatement tests for all the samples despite the differences in their particle sizes and in their crystalline phase distributions obtained without and with the different organic acids used in the synthesis process.CONCLUSIONThe particles synthesized show that the use of organic acids influences the decrease in particle size; moreover, in the case of citric acid, a favourable effect on the appearance of the rutile phase is perceived.All the samples were photoactive and their photocatalytic performance, evaluated under a NO atmosphere, were not negatively affected by the largest particle size (150 nm) nor by the rutile phase content (42 wt.%). © 2022 Society of Chemical Industry (SCI).

Cryogenic 4D-STEM analysis of an amorphous-crystalline polymer blend: Combined nanocrystalline and amorphous phase mapping

SummaryUnderstanding and visualizing the heterogeneous structure of immiscible semicrystalline polymer systems is critical for optimizing their morphology and microstructure. We demonstrate a cryogenic 4D-STEM technique using a combination of amorphous radial profile mapping and correlative crystalline growth processing methods to map both the crystalline and amorphous phase distribution in an isotactic polypropylene (iPP)/ethylene-octene copolymer (EO) multilayer film with 5-nm step size. The resulting map shows a very sharp interface between the amorphous iPP and EO with no preferential crystalline structure near or at the interface, reinforcing the expected incompatibility and immiscibility of iPP and EO, which is a short-chain branched polyethylene. This technique provides a method for direct observation of interfacial structure in an unstained semicrystalline complex multicomponent system with a single cryogenic 4D-STEM dataset.

Electroforming and threshold switching characteristics of NbOx films with crystalline NbO2 phase

Threshold switching (TS) and negative differential resistance (NDR) characteristic of niobium oxide (NbOx) films have been actively studied for neuromorphic computing. Generally, the electroforming process is required for TS and NDR in NbOx films. However, different electroforming and TS properties have been reported for NbOx films with different crystallinities or chemical compositions. This study investigates the effect of thermal annealing on the microstructures of NbOx films and compares the electroforming, TS, and NDR characteristics of amorphous, partially crystallized, and fully crystallized films. The distributions of crystalline NbO2 phase in NbOx films annealed at various temperatures were analyzed using transmission electron microscopy dark-field imaging, and it was observed that the distribution of crystalline NbO2 phase influenced the electroforming process. Moreover, TS characteristics improved in the thermally annealed NbOx films with crystalline NbO2 phases.

RETRACTED: Development of Bulk Metallic Glasses and their Composites by Additive Manufacturing - Evolution, Challenges and a Proposed Novel Solution

RETRACTED ARTICLE: Bulk metallic glasses (BMGs) and their composites (BMGMCs) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very large elastic strain limit. However, they suffer from lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which makes them amenable to failure without appreciable yielding. Various mechanisms and methods have been proposed to counter this effect out of which, recently Additive Manufacturing has gained widespread attention. It is proposed that additive manufacturing can overcome these difficulties in single step due to inherent existence of very high cooling rate in the process which is essential for glass formation. This, when coupled with careful selection of alloy chemistry is proposed to be the best solution to fabricate near net shape parts in a single step with excellent properties. In this report, an effort has been made to describe one possible route to achieve this. Solidification processing employing carefully selected inoculants based on edge to edge matching technique along with the carefuly controlled inoculation procedure is proposed to reflect upon enhanced mechanical properties. It is hypothesized that number density, size and distribution of ductile crystalline phase would best be able to improve microstructure and hence properties. This is meant to be controlled by manipulating type, size and the amount of inoculants. The proposed methodology is claimed to bear maximum potential.

Investigation into surface composition of nitrogen-doped niobium for superconducting RF cavities

Systematic analysis of the surface morphology, crystalline phase, chemical composition and elemental distribution along depth for nitrogen-doped niobium was carried out using different methods of characterization, including Scanning Electron Microscopy (SEM), Atomic-Force Microscopy (AFM), Grazing Incidence X-ray Diffraction (GIXRD), Rutherford Backscattering Spectrometry (RBS) and layer-by-layer X-ray Photoelectron Spectroscopy (XPS) analysis. The results showed that, after nitrogen doping, the surface was covered by densely distributed trigonal precipitates with an average crystallite size of 32 ± 8 nm, in line with the calculation result (29.9 nm) of nitrogen-enriched β-Nb2N from GIXRD, demonstrating the phase composition of trigonal precipitates. The depth analysis through RBS and XPS indicated that β-Nb2N was dominant in the topmost 9.7 nm and extended to a depth of 575 nm, with gradually decreased content. In addition, the successive change along depth in the naturally oxidized states of niobium after nitrogen doping, was revealed. It was interesting to find that the oxygen diffusion depth could be moderately enhanced by the nitridation process. These results established the near-surface phase composition of nitrided niobium, which is of great significance in evaluating the effect of nitrogen doping and further understanding the Q improvement of the superconducting radio frequency cavities.