Amorphous Crystalline Research Articles

One pot and large-scale synthesis of nanostructured metal sulfides: Synergistic effect on supercapacitor performance

Metal sulfides received key interest as an electrode material for storage and conversion of energy. Here, the novel nanostructured N17S18 and (CoNi)3S4 materials were synthesized via one-step hydrothermal method, and the synergistic effect of metal ions and electrochemical properties was investigated. A new and simple solution growth technique was employed in this work. The prepared nanopowders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy techniques. The X-ray diffraction analysis of the prepared nanopowder revealed the formation of cubic phase cobalt nickel sulfides (CoNi)3S4 and hexagonal phase nickel sulfides (Ni17S18). Scanning electron microscopy analysis display fibrous, flakes and sheet-like morphology for CoxSx, N17S18 and (CoNi)3S4, respectively. Fibrous and sheet-like morphology exhibits higher electrochemical performance in supercapacitors. The electrochemical behavior of the amorphous CoxSx, crystallite Ni17S18 and (CoNi)3S4 modified electrodes was investigated using electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge–discharge techniques. The specific capacitance of 57 F/g and 31 F/g were obtained for the amorphous CoxSx and crystalline (CoNi)3S4 powder, respectively. Amorphous CoxSx modified electrode retains 76% of initial capacitance after 1000 repeated cycling process. These results of this study suggest that the CoxSx and crystalline (CoNi)3S4 are appropriate materials for supercapacitor applications.

Heat-Stable and Moisture-Proof CsPbBr3 Quantum Dots Under Dual Protection: Coordination of Non-Crystalline SiO2 and Crystalline h-BN Nanosheets

It’s hard for pure perovskite quantum dots (QDs) to maintain long-term and stable optical properties in practical conditions. Here, CsPbBr3 QDs were first stabilized in amorphous SiO2 and crystalline hexagonal boron nitride (h-BN) nanosheets. The transmission electron microscopy (TEM) images display the laminated structure consisting of CsPbBr3/SiO2 nanospheres and h-BN nanosheets. Besides, the photoluminescence (PL) intensity of CsPbBr3/SiO2/h-BN nanohybrid only has a slight decrease than CsPbBr3/SiO2 nanocomposite. But, dual protection of SiO2 and h-BN give perovskite QDs better humidity stability and thermal stability. Besides, CsPbBr3/SiO2/h-BN block exhibits excellent water-resistance. This work provides a novel method to accelerate the application of perovskite QDs in optoelectronic devices.

Revealing the Strain Effect on Radiation Response of Amorphous–Crystalline Cu-Zr Laminate

Nanocrystalline materials containing amorphous intergranular films (AIFs) exhibit excellent mechanical properties, radiation resistance, and thermal stability and may serve as promising candidate materials for use in advanced nuclear energy systems. The aim of this work is to reveal the effect of mechanical stress on the radiation damage behavior of AIF systems. Based on a bicrystal Cu system with Zr-doped AIFs, molecular dynamics is used to simulate the radiation process and examine the AIF sink efficiency, defect propensity, defect size distribution, and Zr mixing under uniaxial and hydrostatic strain conditions. The results show that the sink efficiency of the glue-like AIFs is not compromised under applied strains. The anisotropy resulting from the intrinsic microstructure and elastic deformation leads to a distinct radiation response, where extension (contraction) of the structure perpendicular to the AIFs increases (decreases) the vacancy density. The strain-dependent defect density, along with the cluster size distributions, can be interpreted based on the variations in the defect formation energy and anisotropic defect diffusion. Finally, the Zr mixing induced by collision cascades is found to be insensitive to the mechanical strains. These findings provide meaningful information towards understanding the stress effect on the radiation response of AIF systems.

Simulation of a-Si:H/c-Si heterojunction solar cells: From planar junction to local junction**Project supported by the National Key R&D Program of China (Grant No. 2018YFB1500403), the National Natural Science Foundation of China (Grant Nos. 11964018, 61741404, and 61464007), and the Natural Science Foundation of Jiangxi Province of China (Grant No. 20181BAB202027).

In order to obtain higher conversion efficiency and to reduce production cost for hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) based heterojunction solar cells, an a-Si:H/c-Si heterojunction with localized p–n structure (HACL) is designed. A numerical simulation is performed with the ATLAS program. The effect of the a-Si:H layer on the performance of the HIT (heterojunction with intrinsic thin film) solar cell is investigated. The performance improvement mechanism for the HACL cell is explored. The potential performance of the HACL solar cell is compared with those of the HIT and HACD (heterojunction of amorphous silicon and crystalline silicon with diffused junction) solar cells. The simulated results indicate that the a-Si:H layer can bring about much absorption loss. The conversion efficiency and the short-circuit current density of the HACL cell can reach 28.18% and 43.06 mA/cm2, respectively, and are higher than those of the HIT and HACD solar cells. The great improvement are attributed to (1) decrease of optical absorption loss of a-Si:H and (2) decrease of photocarrier recombination for the HACL cell. The double-side local junction is very suitable for the bifacial solar cells. For an HACL cell with n-type or p-type c-Si base, all n-type or p-type c-Si passivating layers are feasible for convenience of the double-side diffusion process. Moreover, the HACL structure can reduce the consumption of rare materials since the transparent conductive oxide (TCO) can be free in this structure. It is concluded that the HACL solar cell is a promising structure for high efficiency and low cost.

Boronization‐Induced Ultrathin 2D Nanosheets with Abundant Crystalline–Amorphous Phase Boundary Supported on Nickel Foam toward Efficient Water Splitting

AbstractThe conversion of crystalline metal–organic frameworks (MOFs) into metal compounds/carbon hybrid nanocomposites via pyrolysis provides a promising solution to design electrocatalysts for electrochemical water splitting. However, pyrolyzing MOFs generally involves a complex high‐temperature treatment, which can destroy the coordinated surroundings within MOFs, and as a result not taking their full advantage of their electrolysis properties. Herein, a simple and room‐temperature boronization strategy is developed to convert nickel zeolite imidazolate framework (Ni‐ZIF) nanorods into ultrathin Ni‐ZIF/NiB nanosheets with abundant crystalline–amorphous phase boundaries. The combined experiment, and theoretical calculation results disclose that the ultrathin thickness allows fast electron transfer and ensures increased exposure of surface coordinatively unsaturated active sites while the crystalline–amorphous interface elaborately changes the potential‐determining step to energetically favorable intermediates. As a result, Ni‐ZIF/NiB nanosheets supported on nickel foam (NF) require overpotentials of 67 mV for the hydrogen evolution reaction and 234 mV for the oxygen evolution reaction to achieve a current density of 10 mA cm−2. Remarkably, Ni‐ZIF/NiB@NF as a bifunctional electrocatalyst for overall water splitting enables an alkaline electrolyzer with 10 mA cm−2 at an ultralow cell voltage of 1.54 V. The present work may open a new avenue to the design of MOF‐derived composites for electrocatalysis.

Hierarchical mesoporous ZSM-5 supported nickel catalyst for the catalytic hydrodeoxygenation of anisole to cyclohexane

Upgrading of bio-oil through catalytic hydrotreating was investigated with anisole as a model compound. Hierarchical ZSM-5 zeolites with nano-crystalline structure were successfully synthesized by a segmented steam-assisted crystallization method by tuning the rate of crystallization during the phase transforming between the amorphous structure and crystalline structure without using the organic template. The diffusional properties of ZSM-5 samples were investigated by catalytic cracking of 1,3,5-TIPB. Ni/hierarchical ZSM-5 catalysts displayed an excellent performance in the hydrodeoxygenation (HDO) of biomass-derived anisole to cyclohexane in comparison with conventional Ni/ZSM-5 catalyst. The activity and selectivity were significantly improved by enhancing the accessibility of acidities. Anisole HDO mainly follows the anisole to benzene with metal sites by direct deoxygenation, then cyclohexane formed by hydrogenation.

Effect of the substrate on structure and properties of titanium nitride films grown by plasma enhanced atomic layer deposition

The authors deposited titanium nitride (TiN) films by plasma-enhanced atomic layer deposition on various types of amorphous, polycrystalline, and single crystalline substrates and found that the crystallinity of the substrate strongly affects the morphology, orientation, and resistivity of the films. An appropriate substrate choice yields TiN films with bulk resistivity values of about ∼20 μΩ cm. The preferred crystallographic orientation of the films, either (111) or (001), does not affect film resistivity.

Effects of high-voltage electric field treatment on physicochemical properties of potato starch

The application of a high-voltage electric field (HVEF) is a novel method for starch. First, potato starch slurry (20%, w/w) were subject to HVEF treatment at 10, 20, 30 and 40 kV, and the treatment time was 10, 20, 30, 40, 50 min respectively. Then, the modified starch was characterized by using X-ray diffraction (XRD), Fourier transformation infrared (FT-IR) spectroscopy, pasting behavior, water absorption capacity (WAC), light transmission and scanning electron microscopy (SEM). The results showed that HVEF caused a shift in the gelatinization range to lower temperatures, and a decrease in solubility, swelling power and crystallinity. HVEF was evidenced to change WAC and Light transmittance, with a tendence firstly increase and then decrease with the increasing of the treatment time. The SEM micrographs demonstrated that some roughness or damages emerged on the surface of potato starch granules after HVEF treatments. The X-ray diffraction showed that the decrease of crystallinity during the HVEF treatment. It was concluded that HVEF destroyed amorphous area and surface crystalline zone of starch.

Impact of La2O3/Y2O3 ratio on crystallization kinetics of CaO based alumino-borosilicate glasses and compatibility with Crofer and 8YSZ for SOFCs

In the present investigation, the novel glass series xLa2O3-(10-x)Y2O3-15SrO-15CaO-10B2O3-10Al2O3-40SiO2 (x = 2, 4, 6, 8) has been synthesized by melt quenching technique. The characteristic glass temperatures and the inflection point temperature (Tf) for the glasses have been determined by DTA and differential DTA (DDTA), respectively. The activation energy is calculated using Kissinger, Moynihan and Augis and Benett models. Various kinetic parameters such as fluctuation free volume (fg), Hruby parameter (Hr), bulk thermal expansion coefficient (αf) and k parameters are calculated for studying glass stability with varying La2O3/Y2O3 ratio. The amorphous nature and crystalline phase formation has been studied by X-ray diffraction. Furthermore, the coefficient of thermal expansion (CTE) for all the glasses has been calculated. The interaction studies of the diffusion couples of glasses with pre-oxidized Crofer 22APU and 8YSZ have been carried out at 850 °C. 2 LaY glass is very stable and promising potential sealant for the SOFCs.

Development of Salt Leached Silk Fibroin Scaffold using Direct Dissolution Techniques for Cartilage Tissue Engineering

Autologous transplantations, the gold standard, did not meet sufficient health tissue coverage area for cartilage damage treatments. The field of tissue engineering offers a promising alternative to fulfill this limitation by growing patient own cells on biomaterials through tissue culture, reconstructed into new cartilage tissue, and the implanted to the injury area. To support tissue regeneration, biocompatible, biodegradable, and high strength silk fibroin (SF) was proposed in this study as scaffold materials. In this research, direct dissolution in CaCl2/formic acid, a faster and simpler process than traditional dissolution techniques, combined with salt leaching technique. SF contents on the scaffold were varied from 2 w/v% to 12 w/v% and NaCl size as porogen was fixed in diameter of 250±58 µm. Evaluation of the SF scaffold’s morphology, hydrophilicity, biodegradability, and biocompatibility were conducted. The results showed porous silk fibroin scaffold had been successfully developed. The SF scaffolds have pore size 261-293 µm with highly interconnected pores. FTIR and XRD analysis of the scaffolds showed the characteristics of silk fibroin, which reveals the α-helix amorphous and β-sheet crystalline structure and comparable to the silk fibers. The scaffold showed good hydrophilicity and high water uptakes, which essential properties for cell survival. The scaffold degraded under Protease XIV, indicate biodegradable properties. Observation of cell attachment confirms the scaffold has good biocompatibility to adipose-derived stem cells and are suitable to be used in cartilage tissue engineering.

MCR-ALS analysis of IR spectroscopy and XRD for the investigation of ibuprofen - nicotinamide cocrystal formation.

To improve aqueous solubility, a poorly water-soluble active ingredient is classically combined with a conformer to form cocrystals. Hot melt extrusion is one preparation method for the formation of cocrystal solids. The aim of our study was to determine the optimal temperature conditions for the formation of ibuprofen and nicotinamide cocrystals using real-time infrared (IR) and X-ray diffraction (XRD) measurements. IR spectra and XRD patterns were subjected to multivariate curve resolution alternating least squares (MCR-ALS) analysis and decomposed into several components. Each component was descriptive of a specific step in the formation of the cocrystal. Cocrystal formation was followed by a separation phase between amorphous ibuprofen and crystalline nicotinamide. Our results suggest that, when using the hot melt exclusion method, careful consideration should be made towards optimizing processing temperatures in order to prevent amorphization and promote control over the process of cocrystal formation.

Hydrogen evolution in hydrogenated microcrystalline silicon carbide thin films

Evolved gas analysis (EGA), infrared attenuated reflection (ATR), and Raman spectroscopy experiments are used to study hydrogen evolution in hydrogenated microcrystalline silicon carbide (μc-Si1−xCx:H) films prepared by plasma-enhanced chemical vapor deposition. The results are compared with microcrystalline silicon (μc-Si:H). The effused hydrogen and carbon-hydride groups (CH, CH2, and CH3) are measured up to 800 °C. Their EGA curves have a peak at 410 °C, attributed to the methyl groups incorporated in the amorphous matrix during the deposition process. Moreover, hydrogen evolution curves show narrow and sharp peaks centered at 425 and 520 °C, corresponding to hydrogen desorbing from silicon hydrides at grain boundaries. While its content is more important than hydrogen bonded to silicon in the amorphous and denser crystalline regions of μc-Si1−xCx:H, but remains lower than in the μc-Si:H film. Raman and ATR data indicate that the μc-Si1−xCx:H film is composed of small size silicon crystallites embedded in a hydrogenated amorphous silicon carbide matrix and confirmed that carbon is incorporated in the amorphous matrix as methyl groups (CH3), inducing a decrease in SiHx groups compared to the μc-Si:H film.

A re-examination of experimental evidence on the spectral dependence of the optical transition matrix element associated with thin-film silicon

We analyze the error associated with the optical transition matrix element spectral dependencies for hydrogenated amorphous silicon and crystalline silicon found by Jackson et al. (Phys Rev B 31:5187–5198, 1985). We find that this error is considerable for photon energies less than 1.5 eV. This suggests that spectral dependencies for the optical transition matrix element, other than those proposed by Jackson et al., are possible for photon energies less than 1.5 eV. With this limitation in mind, we then fit a Lorentzian peak to the crystalline silicon experimental optical transition matrix element result of Jackson et al. Within the framework of the damped harmonic oscillator perspective, plotting the term related to the location of the resonant frequency as a function of the damping coefficient, for a number of thin-film silicon experimental results, we have found a relationship between these model parameters. We suspect that this dependence has important implications for the optical response of various forms of thin-film silicon and related materials.

Phase Formation and Magnetic Properties of Melt Spun and Annealed Nd-Fe-B Based Alloys with Ga Additions

The structural transformations and magnetic property changes of the Nd16.2FebalCo9.9Ga0.5B7.5 (SG1, SG2) and Nd15.0FebalGa2.0B7.3 (SG3) nanocomposite alloys obtained by melt spinning in the as-quenched state and after annealing at a temperature range of 560–650 °C for 30 min were studied. The methods used were X-ray diffraction analysis, magnetic property measurements, TEM studies, X-ray fluorescence analysis and Mössbauer spectroscopy. Amorphous phase and crystalline phase Nd2Fe14B (P42/mnm) were observed in the alloy after melt spinning. The content of the amorphous phase ranged from 20% to 50% and depended on the cooling rate. Annealing of the alloys resulted in amorphous phase crystallization into Nd2Fe14B and led to the increased coercivity of the alloys up to 1840 kA/m (23.1 kOe) at 600 °C annealing for 30 min. The alloy with the maximum coercivity had a grain size of the Nd2Fe14B phase ≈50–70 nm with an Nd-rich phase between grains.

Ternary nanoparticle complex of ciprofloxacin exhibiting sustained release at gastric pH prepared by co-complexation with polyanions and an ionic amphiphile

Poor bioavailability of the broad spectrum antibiotic ciprofloxacin (CIP) is caused by its narrow absorption window in the stomach. With the aim of prolonging the gastric residence time of CIP, we prepared a ternary nanoparticle complex (nanoplex) of CIP by co-complexation with polyanions (sodium dextran sulfate (DXT)) and an anionic amphiphile (sodium dodecyl sulfate (SDS)). We investigated the effect of the charge ratio of DXT to SDS on the size, zeta potential, CIP payload, and CIP utilization rate of the CIP-DXT-SDS nanoplex and its dissolution characteristics in simulated gastrointestinal fluids. Fourier transform infrared spectroscopy, powder X-ray diffraction, and differential scanning calorimetry analyses showed that the ternary nanoplex was made up of amorphous CIP-DXT and crystalline CIP-SDS complexes. The size of the CIP-DXT-SDS nanoplex prepared at a >90% CIP utilization rate was 110–290nm and it had a zeta potential of −16–39mV, and CIP payload of 47–62%, depending on the charge ratio. At gastric pH, the CIP-DXT-SDS nanoplex prepared with a DXT:SDS charge ratio lower than 80:20 exhibited prolonged CIP release (60% dissolution after 8h) compared with native CIP (100% dissolution after 1h) and a binary CIP-DXT nanoplex (80% dissolution after 5h), which was attributed to its lower solubility. The sustained release characteristics of the CIP-DXT-SDS nanoplex were comparable to those of existing CIP gastroretentive formulations.

Amorphous Mg–Fe silicates from microwave-dried sol–gels

Context. Laboratory analogues can provide physical constraints to the interpretation of astronomical observations of cosmic dust but clearly do not experience the same formation conditions. To distinguish between properties intrinsic to the material and properties imprinted by their means of formation requires extensive characterisation.Aims. Sol–gel methods can produce amorphous silicates with potentially high reproducibility, but often require long drying times (24+ h) at elevated temperatures in air, controlled atmosphere, or vacuum. We investigate the possibility that microwave drying can be used to form amorphous silicate on a timescale of ∼10 min and characterise their structural and spectroscopic properties relative to silicates produced by other drying methods.Methods. Microwave-dried amorphous MgSiO3, Fe0.1Mg0.9SiO3and Mg2SiO4are characterised using X-ray powder diffraction, total X-ray scattering, small angle X-ray scattering and mid-IR FTIR spectroscopy, and compared to samples produced from the same gels but dried in-air and under vacuum. The development of crystalline structure in the microwave-dried silicates via thermal annealing up to 999°C is also investigated using in situ X-ray powder diffraction.Results. At the inter-atomic level the silicate structures are largely independent of drying method, however larger-scale structured domains, ranging from a ∼few × 10 Å to ∼100’s Å in size, are observed. These are ordered as mass fractals with discernible variation caused by the drying processes. The mid-IR 10μm band profile is also found to be influenced by the drying process, likely due to the way removal of water and bonded OH influences the distribution of tetrahedral species. However, microwave drying also allows Fe to be easily incorporated into the silicate structure. In situ annealing shows that for amorphous MgSiO3crystalline forsterite, enstatite and cristobalite are high temperature phases, while for Mg2SiO4forsterite crystallises at lower temperatures followed by cristobalite at high temperature. For Fe0.1Mg0.9SiO3the crystallisation temperature is significantly increased and only forsterite is observed. Crystalline SiO2may be diagnostic of Mg-rich, Fe-poor grain mineralogies. The results are discussed in relation to the different thermal conditions required for dust to crystallise within protoplanetary disk lifetimes.Conclusions. Sol–gel microwave drying provides a fast and easy method of producing amorphous Mg- and Fe,Mg-silicates of both pyroxene and olivine compositions. Their structure and spectroscopic characteristics although similar to silicates produced using other drying methods, exhibit subtle variations which are particularly manifest spectroscopically in the mid-IR, and structurally over medium- and long-range length scales.

Photocatalytically Active Amorphous and Crystalline TiO2 Prepared by Atomic Layer Deposition

In this work, the photocatalytic properties of amorphous and crystalline TiO2 deposited on oxide and polymer nanoparticles by atomic layer deposition (ALD) were studied. Beside TiO2, as reference, both ALD grown amorphous Al2O3 and crystalline ZnO layers were also examined. When choosing the carrier, the priority was that it had no effect on the photocatalytic activity of TiO2; therefore the oxide layers were deposited on SiO2 and poly(methyl-methacrylate) (PMMA) nanoparticles. The amorphous SiO2 particles were synthetized by the Stöber method, while the PMMA particles were prepared by emulsion polymerization. Both the bare and core/shell composite nanoparticles were investigated by SEM-EDX, TEM, FT-IR, and XRD. Finally, the photocatalytic activity of PMMA, SiO2 and the core/shell nanoparticles was measured by the decomposition of methylene orange, monitored by UV-Vis spectroscopy. Based on the results, the SiO2 was uniformly coated with the deposited oxide films, while in the case of the PMMA a contiguous web-like polymer/TiO2 matrix was formed. During the photocatalytic reactions, the amorphous Al2O3 was not active, while the crystalline ZnO and TiO2 showed good photocatalytic activity. The amorphous TiO2 deposited by ALD on the SiO2 and PMMA nanoparticles had smaller, but a clearly detectable photocatalytic effect on the photodegradation of methylene orange.

The effect of phase structure on the corrosion behavior of Al100-xMox alloy thin films

The corrosion behavior of Al100-xMox alloy (x = 10, 26, 50) films possessed fcc crystalline, amorphous and bcc crystalline phase structure were investigated in 3.5% NaCl solution. The corrosion behavior of Al100-xMox alloy films were controlled by the synergy of composition and phase structure rather than affected merely by the Mo content. The Al74Mo26 film with amorphous phase, compared with Al90Mo10 and Al50Mo50 films with solid-solution crystalline phase, displayed the superior corrosion resistance due to its stable passive film, homogeneous phase structure and proper Mo content. The corrosion mechanisms of Al100-xMox alloy films with different phase structures were illuminated systematically.

Wear mechanism of flexspline materials regulated by novel amorphous/crystalline oxide form evolution at frictional interface

Abstract Flexspline is the most vulnerable component of harmonic drives, and its wear is likely to induce failure. Therefore, this study investigated the tribological properties of three typical flexspline materials with lubricating grease. The evolution of two oxide forms (amorphous FeOOH and crystalline Fe2O3) on a frictional interface was proposed as the wear mechanism, and this mechanism was confirmed using co-analyses of X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. Amorphous FeOOH generated during sliding was observed to enhance the oxide layer, resulting in compact structure and improved toughness that reduced friction at the interface, whereas with insufficient amorphous FeOOH, the frictional crystalline Fe2O3 tended to strip under shear force, destabilizing the oxide layer. The formation ratio of FeOOH/Fe2O3 during sliding regulated the oxide film characteristics and the tribological properties of the materials. Crystalline Fe2O3 partly evolved from amorphous FeOOH is mainly dependent on heat generated during sliding. The grease adsorption properties of tribo-pairs significantly affected the temperature of the frictional contact interfaces. The characteristics of this wear mechanism can be leveraged to reduce wear in future drive designs.

Modeling of high-fluence irradiation of amorphous Si and crystalline Al by linearly focused Ar ions

Long time ion irradiation of surfaces under tilted incidence causes formation of regular nanostructures known as surface ripples. The nature of mechanisms leading to ripples is still not clear, this is why computational methods can shed the light on such a complex phenomenon and help to understand which surface processes are mainly responsible for it. In this work, we analyse the surface response of two materials, a semiconductor (silicon) and a metal (aluminium) under irradiation with the 250 eV and 1000 eV Ar ions focused at 70° from the normal to the surface. We simulate consecutive ion impacts by the means of molecular dynamics to investigate the effect on ripple formation. We find that the redistribution mechanism seems to be the main creator of ripples in amorphous materials, while the erosion mechanism is the leading origin for the pattern formation in crystalline metals.