Changes In Crystal Orientation Research Articles

Hydrogen‐Bond‐Based Polymer‐Ammonium Intermediates Induced Buried Interface Engineering for High‐Performance Inverted Perovskite Solar Cells

AbstractPerovskite interfaces where defects enrich are pivotal for both device efficiency and stability. Herein, a high‐molecular‐weight polyvinyl pyrrolidone (PVP) is proposed as a robust multi‐functional interlayer to engineer the buried interface. Besides the well‐known defect passivation, perovskite crystallization is intriguingly modulated via the formation of hydrogen‐bond‐based polymer‐ammonium intermediates (e.g., PVP‐FA+ or PVP‐MA+, where MA and FA are methylamine and formamidine, respectively). The interaction energies derived from density functional theory calculations (−34.5, −26.8, and −9.9 kcal mol−1 for PVP‐FA+, PVP‐MA+, and PVP‐Pb2+) suggest that PVP predominately interacts with ammonium cations to form the intermediates, thus largely excluding other chemical interactions and retarding the perovskite crystallization. As such, the hydrophilic PVP interlayer leads to spontaneous perovskite spreading yet a counterintuitively similar nucleation density with respect to the hydrophobic poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA), a change of preferred crystal orientation, improved crystallinity, and remarkably suppressed non‐radiative recombination. These conducive effects jointly minimize the open‐circuit voltage loss and give rise to superior power conversion efficiency for small‐area and large‐area devices.

Vapor-transport-deposited Sb2S3 thin-film solar cells: Tailoring photovoltaic properties through deposition temperature

Crystal orientation plays a crucial role in the performance of Sb2S3 thin-film solar cells (TFSCs). Among various deposition techniques, vapor transport deposition (VTD) stands out as a viable technique for producing scalable and uniformly deposited thin films, particularly in the solar industry. This study explores temperature-modulated VTD-Sb2S3 deposition to enable efficient carrier transport in photovoltaic cells. In the VTD process, the deposition temperature is altered between 480 °C and 540 °C. XRD, SEM, EDS, and AFM techniques are employed to obtain the characteristics of the Sb2S3 thin films at varying temperatures and evaluate critical features like crystal structure and orientation, surface morphology, composition, and roughness. The prominent crystal orientation changes from the (hk0) to the (hk1) plane after increasing the deposition temperature from 500 to 520 °C. The (211)- and (221)-planes become more prominent when the deposition temperature exceeds 520 °C. The device with the architecture SLG/Mo/Sb2S3/CdS/i-ZnO/AZO/Al, a substrate-configured TFSC, yields a maximum power conversion efficiency of 0.22% when the VTD-Sb2S3 absorber film is deposited at 520 °C. This study presents a promising approach to producing thin films with a preference for specific crystal orientations. The primary aim is to enhance the efficiency of solar cells that utilize VTD-Sb2S3 absorbers.

The effects of heat treatment and surface state on the corrosion resistance of laser powder bed fusion 304L stainless steel in 3.5 wt% NaCl solution

The corrosion resistance of laser powder bed fusion (LPBF) 304L stainless steel (SS) in 3.5 wt% NaCl solution was evaluated at room temperature through potentiodynamic polarization and electrochemical impedance spectroscopy tests. For electropolished samples, annealing at 1200 °C slightly enhanced the corrosion resistance due to changes in crystal orientation and inclusion composition, and reduced residual strain. In contrast, annealing at 1050 °C significantly reduced the corrosion resistance mainly due to the disappearance of dislocation cells and the remained residual dislocations. Residual stress/strain and martensitic transformation induced by sandpaper grinding can also deteriorate the corrosion resistance. Only the as-received sample shows stable passivation regardless of the surface conditions.

In-situ observation of deformation-induced grain reorientation in 718 Ni alloy microlattices

Microlattices pose ample opportunity for constructing light weight structures for the automotive and aerospace industries. Laser powder bed fusion is an appealing technique to fabricate these structures because of its capabilities to process high-resolution complex architectured structures. In this work we explore the use of a 718 oxide dispersion strengthened alloy to create three microlattice structures designed in nTop, a straight bar, honeycomb and body-centered cubic (BCC) microlattice and investigate the effects of architectures on tensile behavior of the microlattices in a scanning electron microscope. The straight bar configurations deliver high strength but low ductility. The BCC lattices are highly deformable but soft. The honeycomb has an attractive combination of high strength and pronounced work hardening. Furthermore, electron backscattered diffraction studies revealed substantial crystallographic reorientation and grain refinement in the honeycomb lattice during deformation, in contrast to little crystal orientation change in the straight bar specimens. This study suggests that architectures play a significant role in the tensile behavior and deformation mechanisms in metallic materials.

In Situ Study and Improvement of the Temperature Increase and Isothermal Retention Stages in the Polyacrylonitrile (PAN) Fiber Pre-Oxidation Process.

The pre-oxidation process of Polyacrylonitrile (PAN) fibers is a complex procedure involving multiple stages of temperature increase and isothermal temperature retention. However, the impact of the temperature increase stage on PAN fiber has often been overlooked. To address this, samples were collected before and after the temperature increase and isothermal retention stages, treating them as separate influencing factors. Therefore, the pre-oxidation process can be divided into four distinct stages: (1) A temperature increase stage before the cyclization reactions: the PAN fiber's small-size crystals melt, and the crystal orientation changes under fixed tension, leading to shrinkage and increased orientation of the micropore. (2) An isothermal retention stage before the cyclization reactions: The crystal structure maintains well, resulting in minimal micropore evolution. The PAN fiber's crystal orientation and micropore orientation increased under fixed tension. (3) A temperature increase stage after the cyclization reactions: The PAN fiber's crystal melts again, reducing the average chord length and relative volume of the micropore. However, the PAN fiber can recrystallize under fixed tension. (4) An isothermal retention stage after the cyclization reactions: Significant crystal melting of the PAN fiber occurs, but the highly oriented crystals are maintained well. The average chord length and relative volume of the micropore increase. Recommendations for improving the pre-oxidation process are made according to these stages.

Relationship between Crystal Orientation Change and Surface Height Change during Cyclic Tension of Pure Titanium Thin Sheet Specimen after Unloading

Relationship between Crystal Orientation Change and Surface Height Change during Cyclic Tension of Pure Titanium Thin Sheet Specimen after Unloading

Evaluation of Ni–B alloy electroplated with different anionic groups

In order to study the effects of the main nickel salt on the electroplated nanocrystalline Ni–B alloy coating, the deposition rates, surface morphology, crystallinity, grain sizes, hardness, and corrosion resistance of the Ni–B films electrodeposited with plating baths containing separately nickel sulfate (NS) and nickel sulfamate (NSA) under various temperatures and current densities were compared. Under all conditions, the NSA bath system offered higher deposition rates and lower B contents than the NS counterpart because of the formation of Ni-ammonium complex, which can be adsorbed faster than nickel ions. These two groups of coatings had similar surface morphology and crystallinity under all plating conditions except for those plated with the NS bath system at 60 °C, wherein significant changes in surface texture and preferred crystal orientation as well as an abrupt increase in grain size occurred. The coating hardness was optimized by reducing the grain size and increasing the boron content because of the combined effects of grain refinement strengthening and solid solution strengthening. The differences between the two main salt systems can be explained by the presence of ammonium ions in the NSA bath, which not only increased the deposition rate but also maintained the preferred orientation in Ni (111) at high temperature. Our results indicate that, under high current density and high temperature operation conditions, the NSA main salt plating system is a more favorable option for obtaining higher quality Ni–B alloy coatings.

Deformation of columnar calcite within flowstone speleothem

Damaged and faulted speleothems have proven valuable for neotectonic investigations and dating. Flowstone (or “bacon”) speleothems often consist of coarse (cm-scale) columnar calcite with a pronounced primary crystal orientation. However, experimental and microstructural investigations of faulted flowstones are rare. What are the deformation mechanisms in flowstone and how can they be compared to deformation in faulted limestone and marbles is unclear. This study examines deformation mechanisms in flowstone and shows how crystal orientation affects pulverization. Direct shear experiments of columnar flowstone calcite were conducted under room conditions, employing low sliding velocities (1–10 μm/s) and normal stresses (3–10 MPa). The distinctive primary crystal orientation and relatively large crystal size (up to 10 mm) of flowstone allow for an intra- and intercrystalline deformation analysis. The deformation architecture and mechanical strength directly depend on the primary crystal orientation. Mechanical twinning increases in density and thickness, and it accommodates change in crystal orientation. Retrieved samples reveal in-situ pulverization with a drastic grain size reduction, caused by an interplay between mechanical twinning, cleavage and fracture propagation. At relatively small displacements (<10 mm) and strain (0.2) comminution develops a fine gouge. These findings contribute to a better understanding of the behavior of faulted speleothems and their potential implications for neotectonic studies.

Deflecting and routing nematicons via orientation programmable liquid crystal array.

By designing a liquid crystal cell with comb electrode structure, the alignment modulation of nematic liquid crystal in the cell can be realized after the electric field is applied. In different orientation regions, the incident laser beam can deflect at different angles. At the same time, by changing the incident angle of the laser beam, the reflection modulation of the laser beam on the interface of the liquid crystal molecular orientation change can be realized. Based on the above discussion, we then demonstrate the modulation of liquid crystal molecular orientation arrays on nematicon pairs. In different orientation regions of liquid crystal molecules, nematicon pairs can exhibit various combinations of deflections, and these deflection angles are modulable under external fields. Deflection and modulation of nematicon pairs have potential applications in optical routing and optical communication.

Metal Work Function Effects on the Performance of UV–Visible–NIR Cs2SnI6 Photodetectors for Flexible Broadband Application

Herein, the role of top metal electrode work functions on the performance of flexible broadband ultraviolet (UV)–visible–near‐infrared (NIR) flexible Cs2SnI6 (CSI) photodetectors (PDs) are reported in the present study. The change in crystal plane orientation, surface morphology, and chemical composition of prepared films compared to hydrothermally synthesized CSI particles is confirmed by physical characteristics tools. The optical bandgap of CSI films is estimated to be 1.36 eV. The flexible CSI PDs are fabricated with three top metal electrodes (Mo, Ti, and Ni). The current–voltage (I–V) characteristics under the illumination of light sources with different wavelengths reveal the broadband UV–visible–NIR photodetection properties of flexible CSI PDs. The device with top Ti electrodes demonstrates maximum photoresponsivity (Rph = 1.65 ± 0.45 A W−1) and specific detectivity (Dph = 4.53 ± 0.36) × 1010 Jones for 455 nm compared to other wavelengths at Vb = 5 V. The fast photoresponse/decay time is 18 ms/24 ms for 455 nm at Vb = 1 V. The 85% and 90%–95% retentions of Rph of devices after 12 days keeping in a desiccator and after 500 bending cycle tests suggest the device's good environmental stability and mechanical flexibility, respectively. Thus, it is indicated in the results that CSI materials can be a potential candidate for flexible UV–visible–NIR photodetector for wearable electronic device applications.

In Situ Synchrotron X-ray Scattering Investigation of Cathodic ZIF-8 Deposition on Graphite Using 3D-Printed Cells

Electrochemical approaches provide unique means to fabricate thin films of metal-organic frameworks (MOFs). However, the kinetics of electrochemical MOF deposition has not been quantitatively investigated so far. In this study, we report the first in situ measurements of electrochemical MOF growth using transmission synchrotron X-ray scattering. Electrochemical cells based on poly(lactic acid) with two windows were fabricated using fused-deposition modeling. The resulting three-dimensional (3D)-printed cells, the surface of which was coated with paraffin wax to prevent solvent percolation through the polymer material, were used to monitor the cathodic growth of zeolitic imidazolate framework-8 (ZIF-8) on graphite in a methanol solution containing ZnCl2 and 2-methylimidazole (Hmim) at different cathodic potentials. The resulting time-resolved X-ray diffraction data showed a gradual increase in crystal size with negligible changes in crystal orientation during the cathodic ZIF-8 deposition. More importantly, the time-resolved data provided a means to quantitatively assess the kinetics of the cathodic ZIF-8 growth using the Gualtieri model, revealing that the cathodic potential and Hmim concentration affected crystal growth kinetics but not nucleation kinetics. These ZIF-8 samples exhibited changes in X-ray diffraction patterns after being washed with methanol and dried in air, indicating that in situ measurements are essential to investigate mechanisms behind MOF electrodeposition.

Biocompatible Ti3Au–Ag/Cu thin film coatings with enhanced mechanical and antimicrobial functionality

BackgroundBiofilm formation on medical device surfaces is a persistent problem that shelters bacteria and encourages infections and implant rejection. One promising approach to tackle this problem is to coat the medical device with an antimicrobial material. In this work, for the first time, we impart antimicrobial functionality to Ti3Au intermetallic alloy thin film coatings, while maintaining their superior mechanical hardness and biocompatibility.MethodsA mosaic Ti sputtering target is developed to dope controlled amounts of antimicrobial elements of Ag and Cu into a Ti3Au coating matrix by precise control of individual target power levels. The resulting Ti3Au-Ag/Cu thin film coatings are then systematically characterised for their structural, chemical, morphological, mechanical, corrosion, biocompatibility-cytotoxicity and antimicrobial properties.ResultsX-ray diffraction patterns reveal the formation of a super hard β-Ti3Au phase, but the thin films undergo a transition in crystal orientation from (200) to (211) with increasing Ag concentration, whereas introduction of Cu brings no observable changes in crystal orientation. Scanning and transmission electron microscopy analysis show the polyhedral shape of the Ti3Au crystal but agglomeration of Ag particles between crystal grains begins at 1.2 at% Ag and develops into large granules with increasing Ag concentration up to 4.1 at%. The smallest doping concentration of 0.2 at% Ag raises the hardness of the thin film to 14.7 GPa, a 360% improvement compared to the ∼4 GPa hardness of the standard Ti6Al4V base alloy. On the other hand, addition of Cu brings a 315—330% improvement in mechanical hardness of films throughout the entire concentration range of 0.5—7.1 at%. The thin films also show good electrochemical corrosion resistance and a > tenfold reduction in wear rate compared to Ti6Al4V alloy. All thin film samples exhibit very safe cytotoxic profiles towards L929 mouse fibroblast cells when analysed with Alamar blue assay, with ion leaching concentrations lower than 0.2 ppm for Ag and 0.08 ppm for Cu and conductivity tests reveal the positive effect of increased conductivity on myogenic differentiation. Antimicrobial tests show a drastic reduction in microbial survival over a short test period of < 20 min for Ti3Au films doped with Ag or Cu concentrations as low as 0.2—0.5 at%.ConclusionTherefore, according to these results, this work presents a new antimicrobial Ti3Au-Ag/Cu coating material with excellent mechanical performance with the potential to develop wear resistant medical implant devices with resistance to biofilm formation and bacterial infection.Graphical

Influence of Hydrogen on Vintage Polyethylene Pipes: Slow Crack Growth Performance and Material Properties

The distribution of hydrogen and how this can be widely achieved plays a significant role in the transition from fossil fuels to clean fuel. Using the existing natural gas pipeline network can be a suitable option for countries with extensive pipeline infrastructure. This study is aimed at investigating the compatibility of the existing polyethylene (PE) distribution pipe network with hydrogen. This paper utilises the cyclic pennsylvania edge notch test (CPENT) method together with material property measurements including melting point, crystallinity, and oxidative induction time (OIT) to understand the impact of exposing two different PE pipe resins to hydrogen at different exposure times. It was found that exposure to hydrogen has a noticeable impact time to failure, while the bulk crystallinity, OIT, and melting point showed little change. A change in crystal orientation was observed, and this likely accounts for the difference in time to failure when exposed to hydrogen.

Changes in Crystal Orientation and Surface Height after Unloading in Stepwise Load Increasing Repeated Tensile Test of Pure Titanium Thin Sheet Specimen

Changes in Crystal Orientation and Surface Height after Unloading in Stepwise Load Increasing Repeated Tensile Test of Pure Titanium Thin Sheet Specimen

Structural Changes due to Heating and Stress Loading of Metastable Quenched Martensite Structures in Ti–(10–20) mass% Nb Alloys

The metastable-phase characteristics of Ti–Nb alloys can be exploited to improve their functional properties such as damping. In this study, we investigated the structural changes in the metastable quenched martensite structure of Ti–Nb alloys subjected to heating and tensile strain. We examined the differential scanning calorimetry (DSC) heating curves in the reduction state, X-ray diffraction (XRD) profiles under loading/unloading, and material properties such as Young’s modulus and internal friction upon heating. In the DSC heating curve of the 10%-cold-rolled Ti15Nb specimen, an exothermic peak was observed, and for Ti18Nb and Ti20Nb, the exothermic peak exhibited broadening. We speculate that the underlying reason is the biphasic formation resulting from specimen deformation. From the XRD measurements, we found that the lattice tended to shrink upon stress application and recover upon unloading. Significant changes in Young’s modulus and internal friction were observed in the α′′ structures of Ti18Nb and Ti20Nb during initial heating up to 373 K. We posit that the material properties changed owing to structural changes, such as lattice-constant changes, biphasic formation, and crystal orientation changes, resulting from heating or plastic deformation.

Hydrogen Bonding-Induced Crystal Orientation Changes in Confined Microdomains Constructed by Block Copolymer Blends

This study examined crystal orientation confined within a lamellar microdomain morphology formed by the blends of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene-block-poly(acrylic acid) (PS-b-PAA) through wide-angle X-ray diffraction. The hydrogen-bonding interaction between PEO and PAA molecules enabled block copolymers to co-organize into a microphase-separated morphology without inducing macrophase separation, but it hampered PEO crystallization. PEO crystallization that occurred at −20 °C resulted in the nucleation mechanism to be dominant, thus leading to the formation of small crystals. Small crystals allowed them to be free from spatial confinement, and they tended to be oriented with their c-axis parallel to the microdomain interface. By contrast, when PEO was crystallized at 40 °C, the high temperature facilitated PEO crystals to exhibit large crystallite sizes, which aligned perpendicularly to the microdomain interface. An increase in the PS-b-PAA concentration considerably reduced the crystallizability of PEO. The presence of a low amount of crystals and additional lateral confinement formed by hydrogen-bonded PEO/PAA reduced the degree of orientation regardless of the crystallization temperature.

Cation substitution-induced band gap and stability engineering of formamidinium-based perovskite films prepared in ambient conditions

An intermediate complex approach coupled with a preheating strategy are used to grow mixed-cation FA1-xCsxPbI3 perovskite films in ambient air. This was achieved through an effective PbI2 conversion and the elimination of the detrimental moisture effect, which was ensured by the formation of an intermediate complex along with the rapid solvent evaporation induced by the preheating of the substrate and/or precursor solutions. Moreover, it is found that the control of [CsI]/[FAI] ratio clearly influences the crystallization of the α-perovskite phase and could effectively inhibit the growth of non-perovskite crystallites, which stabilizes the photoactive α-phase. X-ray diffraction analyses indicate that a change in crystal orientation from (100) to (111) direction occurs for 35% CsI added in the perovskite precursor, inducing a decrease in the band gap energy. Moreover, the stability is significantly improved in the (111) direction, in agreement with computational results obtained in literature.

Chromium doped tungsten alloy for plasma-facing components of fusion reactors formed by compression plasma flows

Chromium doped tungsten (Cr-W) alloys are formed by compression plasma flows (CPFs) treatment at different absorbed energy densities (20 – 50 J/cm2), and are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDX), and the Vickers hardness test. XRD analysis betokens that the dominant crystal orientation changes from (110) to (200) after CPFs treatment, and the intensity ratio (I200/I110) between the diffraction lines corresponding to (200) and (110) planes increases with an increase in the absorbed energy density. SEM and EDX analyses betoken spatial inhomogeneity at 20 J/cm2, improved uniformity at 30 J/cm2, and cracks at higher energy density. The hardness of the Cr-W alloy varies with absorbed energy density and has a maximum value of 379 HV at 20 J/cm2.

Addition of Diquat Enhances the Electron Mobility in Various Non‐Fullerene Acceptor Molecules

AbstractMolecular doping of organic semiconductors is often used to enhance their charge transport characteristics. Despite its success, however, most studies to date concern p‐doping with considerably fewer reports involving n‐dopants. Here, n‐doping of organic thin‐film transistors (OTFTs) based on several non‐fullerene acceptor (NFA) molecules using the recently developed diquat (DQ) as a soluble molecular dopant is reported. The low ionization potential of DQ facilitates efficient electron transfer and subsequent n‐doping of the NFAs, resulting in a consistent increase in the electron field‐effect mobility. Solution‐processed BTP‐eC9 and N3‐based OTFTs exhibit significant increase in the electron mobility upon DQ doping, with values increasing from 0.02 to 0.17 cm2 V–1 s–1 and from 0.2 to 0.57 cm2 V–1 s–1, respectively. A remarkable electron mobility of &gt;1 cm2 V–1 s–1 is achieved for O‐IDTBR transistors upon optimal doping with DQ. The enhanced performance originates primarily from synergistic effects on electronic transport and changes in morphology, including: i) significant reduction of contact resistances, ii) formation of larger crystalline domains, iii) change of preferred crystal orientation, and iv) alteration in molecular packing motif. This work demonstrates the universality of DQ as an electronic additive for improving electron transport in OTFTs.

Unraveling the role of operating pressure in the rapid formation of Cu-BDC MOF via a microdroplet approach

A microdroplet-based spray process has been recently developed for the synthesis of metal–organic frameworks (MOFs) which features a short processing time and scalable manner. In this process, atomized microdroplets of the MOFs precursor solution undergo well-controlled physiochemical transformations with each droplet serving as a microreactor. Droplet transformation is closely related to the flow patterns of the spray system. A conventional spray system is operated at atmospheric pressure (under the continuum flow regime). By lowering the operating pressure, the spray system is transitioned to a free-molecular flow regime, where the transport phenomena of the microdroplet become distinct due to the discrete surrounding gas. It is hypothesized that the MOFs formed under this condition could have unique morphological and structural features. Nevertheless, this topic has rarely been investigated. This work studies the formation of the copper 1,4-benzenedicarboxylate (Cu-BDC) MOF under changing flow regimes by modulating the operating pressure. Specifically, changes in crystal size, morphology, and orientation, as well as surface oxidation state, are observed with decreasing operating pressure. Heat and mass transfer calculations, accounting for the transition of flow regimes, suggest that these variations are related to different evaporation rates of the microdroplets. Our study also suggests that the dissociation of solvent molecules from Cu-BDC under sub-ambient pressure increases open metal sites which lead to a strong CO2 binding affinity. This work illustrates the synthesis of MOFs under substantially low operating pressures and offers many new opportunities in the controlled synthesis of MOFs for selective gas adsorption.