Nanocrystalline Structure Research Articles

AMachine-Learning-Based Approach for Solving Atomic Structures of Nanomaterials Combining Pair Distribution Functions with Density Functional Theory.

Determination of crystal structures of nanocrystalline or amorphous compounds is a great challenge in solid-state chemistry and physics. Pair distribution function (PDF) analysis of X-ray or neutron total scatteringdata has proven to be a key element in tackling this challenge. However, in most cases, a reliable structural motif is needed as astarting configuration for structure refinements. Here, an algorithm that is able to determine the crystal structure of an unknown compound by means of an on-the-fly trained machinelearning model,whichcombines density functional theory calculations with comparison of calculated and measured PDFs for global optimization in an artificial landscape, is presented. Due to the nature of this landscape, even metastable configurations and stacking disorders can be identified.

Microscopic studies on transparent AlSiN ternary hard coating

In this work AlSi nanocomposite coating were deposited by RF magnetron sputtering in Ar/N2 reactive atmosphere. AlSi alloy target of composition 86:14 wt % have been used to deposit the coating on float glass substrate by varying the deposition time: starting from 0.5 h to 2 h. The substrate temperature and target power were fixed at 250 °C and 100 W respectively. The effect of deposition time on microstructure, mechanical and optical property were studied by usingX-ray Diffraction (XRD), Stylus profiler, Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), UV–Visible Spectrometer and Nanoindentation techniques. The XRD shows the formation h-AlN phase for film deposited for 2 h which shows that with increase in deposition time, the film structure changes from amorphous to polycrystalline, the coating deposited for 2 h develops wurtzite-AlN nanocrystalline structure. The thickness of the coating increases with respect to the increasing deposition time which was confirmed from stylus profiler. The FESEM study shows the uneven and randomly oriented grains present in the coating. TEM study confirms the amorphous and polycrystalline nature of the films with low and high thickness respectively. The elemental composition was confirmed by EDS. UV–Visible Spectrometer delivers the optical transparency of the film which is >90% for all the coatings in the visible range spectra. The roughness of the samples was also measured from scanning probe microscope image, which showed average roughness (Rã) value below 2 nm. The maximum hardness obtained is 31 GPa for the coating deposited 2 h with 490 nm thickness, it has an elastic recovery of 92% which suggest its resistance to elasticity as well as plastic deformation.

Molar-Fraction-Tunable Synthesis of Ag–Au Alloy Nanoparticles via a Dual Evaporation–Condensation Method as Supported Catalysts for CO Oxidation

The properties of nanoparticles composed of two metallic elements are affected by their synergy as well as the composition and structure of nanocrystals. Therefore, precise adjustment of the molar fractions of the constituent elements and crystal structure is required for their successful synthesis. An evaporation–condensation method, which represents an aerosol nanoparticle synthesis method, is based on the reagglomeration of metallic elements in the gas phase. In this study, we utilized a dual evaporation–condensation method with two furnaces to adjust the molar fractions of Ag–Au nanoparticles with an alloy-type nanocrystalline structure and obtain spherical particles with sizes smaller than 10 nm. The molar fraction of Ag atoms in the synthesized particles varied between 0 and 80% depending on the heating temperature. Energy-dispersive X-ray spectroscopy data revealed that Ag and Au elements were present in all particles and formed an alloy structure, suggesting that alloyed composite particles with different stoichiometries can be easily fabricated via the dual evaporation–condensation method. In addition, the nanoparticles generated in the gas phase were successfully recovered by immobilization on a substrate and served as effective bimetallic catalysts for CO oxidation. It is noteworthy that the preparation of nanoparticles and their fixation to a substrate in the proposed method were performed in one step.

Substrate-dependent fractal growth and wettability of N+ ion implanted V2O5 thin films

Wettability of active material surface affects the electrolyte and electrode-material interaction in electrochemical applications. An increase in the V2O5 electrode's wetting behaviour allows for better contact with the electrolyte. The surface properties of the V2O5 sample were examined in order to evaluate its wettability. In this work, the surface growth of V2O5 thin films on three different substrates (glass, silicon, and sapphire) after 16 keV N+ ion implantation is presented as a function of ion dose. Thin films of 500 nm V2O5 deposited on different substrates show the formation of the nanocrystalline structure over the surface after thermal annealing. Silicon substrate shows the formation of V2O5 nanorods over the surface. Surface morphology shows the growth dynamics of the surface in terms of roughness (α) and growth (β) exponents. Lateral growth of surface features has been quantified in terms of co-relation length (ξ) and fractal dimensions (Df). The scaling laws studies of the surfaces in terms of exponents and co-relation length shows the role of N+ implantation in structural modifications. Furthermore, wetting dynamics have been co-related with fractal growth of the films under ion implantation. The contact angle of V2O5 thin films is found to be higher for V2O5 nanorods on silicon substrate as compared to crystallite grains on sapphire. The present study showed that the surface morphology and wettability of V2O5 are mainly substrate-dependent and can be controlled by surface fractal parameters.

Influence of high hydrostatic pressure on protein clustering: Implications for processing and macroscopic crystallization.

High pressure (HP) is used in various industrial applications to sterilize a product stream or to confer desired properties. HP is also present during freezing processes, yet relatively little is known about its effects on protein phases. Protein clustering has been well-documented as a precursor to liquid-liquid phase separation (LLPS) and macroscopic crystallization. Several globular proteins have been previously shown to salt-out in the presence of ammonium sulfate, with clustering observed when approaching a first aggregation boundary, phase separation beyond a second aggregation boundary, and gel bead nucleation between them. Nanocrystalline structures have been observed within the salted-out macroscopic gels, suggesting clusters below the first aggregation boundary are precursors to macroscopic crystals. The present work examines the influence of pressures up to 400 MPa on salt-induced clustering in ovalbumin solutions on either side of the first aggregation boundary. Small-angle x-ray scattering (SAXS) on aged solutions approaching the boundary reveals the presence of protein clusters, and a computational deconvolution into fractional oligomer population contributions to scattering was used to assess salt-induced clustering with similar characteristics on either side of the first aggregation boundary. Surprisingly, HP-SAXS on fresh samples reveals a sharp shift in pressure effects on clustering across the boundary. The discrepancy in pressure response suggests a fundamental difference in the clustering mechanism across the first aggregation boundary, and that clusters in this region are early nucleated gels rather than crystal precursors. The current results are of interest to protein processing and LLPS, providing insights into competing mechanisms of protein aggregation and suggesting pressure-dictated clustering as a potential tool for controlling macroscopic phase behavior.

Core-shell structure and stability of nanocrystalline precipitates in Fe83.3Si4B8P4Cu0.7 soft magnetic amorphous alloy

The core-shell nanostructure of α-Fe precipitates was investigated in a recently developed high-performance Fe83.3Si4B8P4Cu0.7 nanocrystalline soft magnetic alloy utilizing small-angle neutron scattering (SANS) and atom probe tomography (APT). SANS measurements under a saturating magnetic field provided evidence of core-shell structures at the nanoscale. Moreover, the core-shell structure was directly visualized from APT analysis, where P-enriched shells were found around Fe-enriched cores due to the large negative heat of mixing between Fe and P elements and the slow diffusion of P atoms. The core-shell nanostructures induced by nanoscale partitioning are effective in stabilizing the residual amorphous matrix and suppressing the crystal growth. Our findings provide insight into the microstructure of Fe-based amorphous alloys and have direct implications in alloy design for the improvement of the soft magnetic properties.

The Mode Deformation Effect on Surface Nanocrystalline Structure Formation and Wear Resistance of Steel 41Cr4

A surface nanocrystalline steel layer in the low alloy steel 41Cr4 was fabricated by using mechanical-pulse treatment (MPT) with different deformation modes. The structure parameters, the physical and mechanical properties, the wear resistance, and the surface topography parameters of the treated steel depending on the deformation mode were investigated. A tool with a smooth working surface was used for inducing unidirectional deformation in the top surface layer (shear), and a tool with the oppositely directed grooves was used for generating multidirectional deformation. The surface layer with a nanocrystalline structure formed by MPT using both of the tools was characterised by enhanced mechanical properties and wear resistance compared with those of the untreated or heat-treated steels. Inducing multidirectional deformation during the MPT resulted in a decrease in the grain size and an increase in the depth and microhardness of the surface layer due to it facilitating the generation of dislocations compared to those formed under unidirectional deformation. The results also demonstrated that favourable surface topography parameters providing the highest wear resistance of the steel were obtained at MPT using multidirectional deformation.

Indium Oxide Powder Synthesis in a Low-Current Discharge Plasma at Atmospheric Pressure

The results of a study of the processes involved in the production of indium oxide In2O3 powder, which is widely used to create transparent and electrically conducting ceramics, are described. The powder was produced in a flow of rare gas (argon or helium) at atmospheric pressure under conditions for the formation of metal-containing plasma in a non-arc discharge mode. The discharge operated in pulsed mode with a pulse repetition rate of 70 kHz and pulse duration of 12 μs. The discharge current was 670 mA and discharge voltages were 180 V and 250 V when the working gases were argon and helium, respectively. These parameters ensure a mode in which the indium cap of a molybdenum cathode suffers thermal erosion. The morphology and elemental and phase composition of the erosion products were studied using transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analysis. It was shown that the structure of the synthesized powder particles corresponded to a phase of indium oxide (III) with a body-centered cubic (bcc) lattice with lattice parameter a = 1.013 nm. The powder particles, regardless of the working gas (Ar or He), consisted of non-stoichiometric indium oxide In2O3 with a nanocrystalline structure. The average particle diameter was <d> = 13–16 nm.

Deformation mechanism and mechanical properties of TiN/ZrN nanolaminates by nanoindentation: effect of layer thickness and temperature

Mechanical performance of ceramic/ceramic nanolaminates at elevated temperatures is a main concern when they are applied as protective coatings on compressed blades of aeroengines. In this work, the deformation mechanism and mechanical properties of physical vapor deposited TiN/ZrN nanolaminates are studied by instrumented nanoindentation at 25–450 °C. The effects of layer thickness and temperature are highlighted, with the help of detailed microstructural characterizations. The results show a cracking activity of individual layers for nanolaminates with 50 nm thick layers at 25 °C, which is detrimental to the mechanical performance and arises a strong indentation size effect. In addition, due to nanocrystalline structures of both TiN and ZrN layers, reduction of layer thickness is not effective to strengthen the nanolaminate. As a result, ‘the thinner, the stronger’ rule that works for most nanolaminates does not hold for the specific TiN/ZrN system. The indentation cracking activity is prohibited at elevated temperature due to thermally activated plasticity of both layers. An approximate linear softening in modulus and hardness, as determined by nanoindentation, is observed. Based on the high temperature data, ‘apparent’ activation energy for TiN/ZrN nanolaminate is finally quantified. The work may forward the advance of novel ceramic/ceramic nanolaminates in hot-section components of aeroengines.

Effects of Si on the microstructure, soft magnetic properties and bendability of rapidly-annealed nanocrystalline Fe–Si–B–P–Cu alloy ribbons

The high Fe-content Fe–Si–B–P–Cu nanocrystalline alloys obtained by annealing the amorphous/nanocrystalline precursors are brittle and their magnetic properties are sensitive to the annealing process, which are disadvantageous for the practical applications of the alloys. In this study, the effects of Si on microstructure, soft magnetic properties and bendability of the rapidly-annealed Fe83SixB14−xP2Cu1 (x = 2–6 at%) nanocrystalline ribbons were investigated, and the properties of the nanocrystalline alloys with different Si contents were discussed in correlation to the structural evolution and element distribution. It was found that the partial substitution B with Si in the Fe–Si–B–P–Cu alloy system could promote the primary crystallization of α-Fe(Si) grains and suppress the precipitation of the hard-magnetic Fe-metalloid phase, thus widening the optimum annealing temperature (Top) ranges for preparing the alloys with high saturation magnetization (Bs) and low coercivity (Hc). The alloys rapidly annealed at Top for 30 s possess fine and uniform amorphous/α-Fe(Si) nanocrystalline structure, and exhibit good soft magnetic properties including high Bs of 1.80–1.85 T and low Hc of 5.2–7.2 A/m. Furthermore, the atom probe tomography (APT) results indicated that the distribution of Si in the nanocrystalline alloys is more uniform than that of B. The substitution of B with Si could decrease the compositional inhomogeneity, contributing to an improvement of bendability for the alloys with higher Si contents.

Self-Assembly of Nanocrystalline Structures from Freestanding Oxide Membranes.

The exploration of crystalline nanostructures enhances the understanding of quantum phenomena occurring in spatially confined quantum matter and may lead to functional materials with unforeseen applications. A novel route to fabricating nanocrystalline oxide structures of exceptional quality is presented. This is achieved by utilizing a self-assembly process of ultrathin membranes composed of the desired oxide. The thermally induced self-assembly of nanocrystalline structures is driven by dewetting the oxide membranes once they are lifted off and transferred onto sapphire surfaces. In three successive steps, the process provides nanovoids, nanowires, and nanocrystals. Regardless of substrate orientation, the nanostructures are highly anisotropic in shape due to material retraction favoring low-index crystalline lattice directions of the membranes. The orientation of the nanostructures is provided precisely by the crystal lattice of the transferred membrane. The microstructure of the nanocrystals exhibits exceptional quality, characterized by a pristine crystal structure and uniform stoichiometry, both maintained all the way down to the well-developed crystalline facets. The demonstrated self-assembly process holds the potential to improve the understanding of surface diffusion phenomena at the interface of materials, which is important for advancing epitaxial growth technology and paves the way to fabricating crystalline nanostructures by the transfer and self-assembly of membranes.

Evolution of Structure and Properties of Nickel-Enriched NiTi Shape Memory Alloy Subjected to Bi-Axial Deformation.

The effect of a promising method of performing a thermomechanical treatment which provides the nanocrystalline structure formation in bulk NiTi shape memory alloy samples and a corresponding improvement to their properties was studied in the present work. The bi-axial severe plastic deformation of Ti-50.7at.%Ni alloy was carried out on the MaxStrain module of the Gleeble system at 350 and 330 °C with accumulated true strains of e = 6.6-9.5. The obtained structure and its mechanical and functional properties and martensitic transformations were studied using DSC, X-ray diffractometry, and TEM. A nanocrystalline structure with a grain/subgrain size of below 80 nm was formed in bulk nickel-enriched NiTi alloy after the MaxStrain deformation at 330 °C with e = 9.5. The application of MaxStrain leads to the formation of a nanocrystalline structure that is characterized by the appearance of a nano-sized grains and subgrains with equiaxed and elongated shapes and a high free dislocation density. After the MaxStrain deformation at 330 °C with e = 9.5 was performed, the completely nanocrystalline structure with the grain/subgrain size of below 80 nm was formed in bulk nickel-enriched NiTi alloy for the first time. The resulting structure provides a total recoverable strain of 12%, which exceeds the highest values that have been reported for bulk nickel-enriched NiTi samples.

The structure of the contact zone of the surfacing-substrate subjected to electron-beam processing

Using scanning and transmission electron microscopy, the analysis of the structure, phase and elemental composition of the contact zone of the system coating (high-entropy FeCrCoNiMn alloy)-substrate (5083 alloy) after electron-beam processing was performed. The formation of a multiphase, multielement submicro- and nanocrystalline structure has been established. The structure of high-speed cellular crystallization in the contact layers adjacent to the coating and substrate is revealed, and the formation of lamellar crystals in the central region of the contact zone is also found. Keywords: contact zone, high-entropy alloy, wire-arc additive manufacturing method, 5083 aluminum alloy, pulsed electron beam, elemental and phase composition, structure.. Keywords: contact zone, high-entropy alloy, wire-arc additive manufacturing method, 5083 aluminum alloy, pulsed electron beam, elemental and phase composition, structure.

Структура зоны контакта наплавка-подложка, подвергнутой электронно-пучковой обработке

Using scanning and transmission electron microscopy, the analysis of the structure, phase and elemental composition of the contact zone of the system coating (high-entropy FeCrCoNiMn alloy)-substrate (5083 alloy) after electron-beam processing was performed. The formation of a multiphase, multielement submicro- and nanocrystalline structure has been established. The structure of high-speed cellular crystallization in the contact layers adjacent to the coating and substrate is revealed, and the formation of lamellar crystals in the central region of the contact zone is also found. Keywords: contact zone, high-entropy alloy, wire-arc additive manufacturing method, 5083 aluminum alloy, pulsed electron beam, elemental and phase composition, structure.

Facile auto-combustion synthesis of nanocrystalline BaCoFe6O11-Structural and Optical properties

The BaCoFe6O11 (Barium cobalt hexairon (III) oxide) is efficiently synthesized by modified single-step auto-ignition combustion route. The sample crystallized under trigonal structure with a space group R3-m with hexagonal axes obtained from XRD. The XRD determined crystallite size is 10 nm, which is corroborated by the Hall-Williamson plot and Modified Scherrer technique. Fourier transform infrared spectroscopy is used to identify the functional group and confirm the phase purity of the sample. Transmission electron microscopy images indicate the sample’s nanocrystalline structure. Additionally, FE-SEM is used to analyse the surface morphology of the material. The optical band gap energy are estimated by using UV–visible spectroscopy and also calculated by Tauc’s plot and Kubelka-Munk function. Photoluminescence emission peaks in the visible region as well as band gap energy values, confirms the sample’s practicality in optoelectronic devices.

Structure of the surface layer of high-chrome steel nitridated in the elion regime in the plasma of a suspended arc discharge with a heated cathode

The purpose of this work is to reveal the patterns of formation of the structure of the surface layer of high-chromium steel subjected to nitriding in a low-pressure gas discharge plasma using a plasma generator with a hot cathode "PINK". Heating of the samples to the nitriding temperature was carried out by the ionic component of the plasma, as well as by the electron and ionic components of the plasma (elion mode). The object of the study was heat-resistant corrosion-resistant steel of the austenitic class grade 20X23H18 (foreign analogue of AISI310S). The relevance of research is due to the relatively low level of hardness and wear resistance of steels of this class. Nitriding of steel was carried out on the TRIO installation, retrofitted with a switching unit for implementing the aelion (electronic and ionic) processing mode. It has been established that the thickness of the hardened layer is (55-60) pm and weakly depends on the method of nitriding, temperature (in the range of 793-873 K), and duration (3-5 hours) of the process. A nitriding regime has been revealed that makes it possible to form a surface layer with a microhardness of 13.7 GPa (ionic heating mode) and 10.8 GPa (elion heating mode). It has been established that the high strength and tribological properties of nitrided steel are due to the formation of a nanocrystalline structure in the surface layer, the main phases of which are iron nitrides Fe4N and chromium nitrides CrN. It is shown that heating the samples to the nitriding temperature in the aelion mode, which uses the electron and ion components of the plasma, leads to a significantly lower level of material roughness compared to the samples heated during nitriding by the ion component of the plasma.

Nanostructured Zn0.1Co2.9O4 material: Synthesis, characterization and its applications for energy storage and electrocatalytic dye degradation

This article presents the synthesis and characterization of a cobalt oxide nanomaterial with potential applications in dye degradation and energy storage. The nanomaterial, Zn-doped cobalt oxide (Zn0.1Co2.9O4), was synthesized using a coprecipitation method followed by calcination at 300 °C for 5 h. Various techniques including XRD, TEM, and BET were employed to analyze the phase formation, particle size, morphology, and surface area of the calcined sample. The XRD analysis confirmed the phase purity of the material, revealing a nanocrystalline structure with an average crystallite size of 10 nm. TEM imaging revealed spherical-shaped particles with a mean particle size of 11 nm. The material exhibited mesoporous characteristics, with a surface area of 60 m2/g and a pore size of 33 nm according to BET analysis. Cyclic voltammetry (CV) measurements conducted at different scan rates demonstrated the redox behavior of the material, as evidenced by the presence of oxidation and reduction peaks. Galvanostatic charge–discharge (GCD) experiments revealed a specific capacitance (Cs) of 117 F/g at a current density of 0.1 A/g, which decreased to 78 F/g at 1 A/g. The electrocatalytic dye degradation of methyl orange dye (5 ppm) was carried out using a stainless steel electrode coated with the Zn0.1Co2.9O4 nanomaterial. An applied potential of 15 V and a current of 0.03 A resulted in a 98% degradation of the dye after 30 min. The experiment was repeated for five successive cycles, yielding consistent levels of dye degradation.

Fabricating FeCrCoZrLa High Entropy Alloy towards Enhanced Photocatalytic Degradation of Methylene Blue Dye

Fe20Cr20Co20Zr20La20 (at. %) high entropy alloy (HEA) using mechanical alloy (MA) was synthesized by an equiatomic ratio as a function of milling times (0h, 5h, 10h, 20h, 30h, and 50h). The HEA alloys were characterized with X-ray diffractometer (XRD), scanning electron microscopy (SEM), X-ray Energy-Dispersive Spectroscopy (EDX), transmission electron microscopy (TEM), and Differential thermal analysis (DTA). After 50 hours of grinding, the BCC crystalline phase was formed and the crystallite size and microstrain were calculated at 4.7 nm and 1.95 nm, respectively. TEM image of 50 hours of milled powders also confirms a nanocrystalline structure. Using solar energy, visible light photocatalysis is a promising method for removing environmental pollution. The photocatalytic effect of the synthesized nanostructured alloy on aqueous solutions containing methylene blue (MB) was investigated under xenon light. Photocatalytic degradation of the synthesized sample was evaluated by calculating the absorbance drops of the UV–Vis absorption spectra (methylene blue 664 nm).The degradation of the nanostructured alloy for MB was found as 89.76% after 120 min. This implies that the photocatalytic degradation rate is relatively high, and the obtained alloy has been used in practice for the degradation of methylene blue dye effectively.

Achieving stable actuation response and elastocaloric effect in a nanocrystalline Ti50Ni40Cu10 alloy

Shape memory alloys with good functional fatigue property are in demand in practical applications such as solid-state actuators and eco-friendly refrigerators. In the present study, the functional stability of Nitinol (Ti-Ni alloy) was improved by combining Cu-doping and nanocrystallization. The target alloy maintains almost constant transformation temperatures in both stress-free and load-biased thermal cycles, showing a stable thermal actuation response. Moreover, a large adiabatic temperature change of over 20 K is obtained without much degradation in the course of 200 tensile cycles. The detailed microstructural observation reveals that the excellent functional stability in the alloy originates from both the improvement of lattice compatibility brought about by doping and the strengthening effect provided by the nanocrystalline structure.

Методы исследования параметров биогенных металлических наночастиц, формирующихся in situ

We propose an innovative method for assessing the integral level of metabolic activity of biological objects, based on the natural ability of living cells for generation metal nanoparticles from cations sources (artificially introduced into the samples), while in sterile samples or in the presence of inactive cells, the formation of nanoparticles does not occur. The method is called DBNG (detection of biogenic nanoparticles generation/growth). This article presents several examples of the use of the main analytical approaches applicable to obtain information about the parameters of biogenic nanocrystalline structures that formed in situ(directly in the tested samples), as well as options for the practical use of the proposed nanobiotechnological innovative approach DBNG to assess (estimate) the basic integral properties of living cells.