Average Domain Size Research Articles

Some geometrical aspects of diffracted waves formation on a reconstructed crystal face at RHEED

The evolution of RHEED reflections intensity during reconstruction transitions characterizes (often implicitly) reconstructed surface state change peculiarities. The approaches of a correct RHEED data interpretation, aimed at obtaining information about reconstruction transitions kinetics, are considered in the present work. In particular, the nature of RHEED reflections formation, depending on such parameters as the average size of reconstruction domains and number of such domains per area unit, is analyzed within the kinematic approximation of the diffraction theory. This geometrical description, in complex with the JMAK model, is a convenient and effective (productive) way of analyzing reconstruction transitions mechanisms and parameters.The transformation of the functional dependence between the measured values (RHEED pattern reflections intensity) and the degree of surface coverage by reconstruction domains, at a change of these domains average size and distribution density, is shown. The correctness of theoretical conclusions is confirmed by the obtained experimental results, and it well agrees to the known literature data. This work provides the community with a useful framework for such type of theoretical studies.

The microstructural evolution of chemical disorder and ferromagnetism in He+ irradiated FePt3 films

This paper investigates the role of ion-induced disorder on the morphology and magnetic properties of chemically ordered FePt3 films. The effects are studied for 15 keV He+ ions as a function of the ion fluence for 0, 2 × 1016 and 2 × 1017 ions cm−2. Substitutional mixing of the L12-type Fe-Pt sites takes place within the region of the chemically ordered FePt3 film affected by the irradiation. This accompanies a paramagnetic-to-ferromagnetic transition, as determined by room-temperature magnetometry. Dark-field transmission electron microscopy (TEM) measurements confirm that the 15 keV He+ ions induce a 120 nm-thick chemically disordered layer into the sub-surface region of the nominally 280 nm-thick ordered FePt3 film. The average domain size and the fractional density of the chemically ordered domains within the irradiated FePt3 microstructure are found to mutually decrease with increasing ion fluence. Selected-area electron diffraction results demonstrate that the film’s single crystallinity is preserved after irradiation, irrespective of the ion fluence. High-resolution TEM elucidates the coexistence of ordered domains and precipitate disordered domains in the near-surface, low-ion impacted regions of the FePt3 film. Collectively, this work provides detailed insights into the material-science relationship between ion-induced disorder and ferromagnetism in FePt3, as a step towards creating fully customisable, ion-beam-synthesised magnetic nano-elements.

The effect of titanium dioxide synthesis technique and its photocatalytic degradation of organic dye pollutants

Nanostructured mesoporous titanium dioxide (TiO2) particles with high specific surface area and average crystallite domain sizes within 2 nm and 30 nm have been prepared via the sol-gel and hydrothermal procedures. The characteristics of produced nanoparticles have been tested using X-Ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, Scanning Electron Microscopy (SEM), Fourier Transform Infra-Red (FTIR), and Raman Spectroscopy as a function of temperature for their microstructural, porosity, morphological, structural and absorption properties. The as-synthesized TiO2 nanostructures were attempted as catalysts in Rhodamine B and Sudan III dyes' photocatalytic decomposition in a batch reactor with the assistance of Ultra Violet (UV) light. The results show that for catalysts calcined at 300 °C, ∼100 % decomposition of Sudan III dye was observed when Hydrothermal based catalyst was used whiles ∼94 % decomposition of Rhodamine B dye was observed using the sol-gel based catalysts. These synthesized TiO2 nanoparticles have promising potential applications in the light aided decomposition of a wide range of dye pollutants.

Combined texture and microstructure analysis of deformed crystals by high-energy X-ray diffraction

It is shown that high-energy X-ray diffraction allows a fast and accurate texture and microstructure analysis of crystals, which can help to set up optimal industrial procedures for materials manufacturing. This paper presents the experimental and theoretical aspects of quantitative texture analysis using high-energy synchrotron beams. Intensity corrections are less important in this approach than in classical laboratory methods; however, the most important correction, related to the Lorentz factor, can introduce relative fraction changes of up to about 40% compared to the uncorrected case. The resolution of the orientation density function also influences the results. For example, the usual 5° resolution leads to relative deviations of up to 30% in the fraction of some components. The method allowed detection of small changes taking place during the recovery and continuous recrystallization of a cold-rolled Al–TiB2 nanocomposite. Texture information was combined with the results of line profile analysis, evidencing the evolution of the average dislocation density and coherent domain size of the selected grain families. It was found that recovery, as described in terms of dislocation annihilation and coherent domain coarsening, takes place at similar rates in all components.

The Reducibility and Cluster Size of Vanadium Oxide as Potential Descriptors of Its Catalytic Activity in the Partial Oxidation of Ethanol

Abstract A series of vanadium oxide (VOx) catalysts prepared using three different supports were tested for the partial oxidation of ethanol to acetaldehyde. Optical absorption spectroscopy and Temperature Programmed reductions experiments indicate that the reducibility and average domain size of the vanadia clusters anchored on the supports are very sensitive to vanadia loading. The catalytic activity results were modeled using a pseudo steady state approximation using the ethanol hydrogen abstraction step as rate limiting. The results obtained strongly suggest that catalytic activity can be correlated to both average vanadia cluster size and the ability of vanadia to uptake hydrogen during TPR experiments.

Local Structure of Zr(OH)4 and the Effect of Calcination Temperature from X-ray Pair Distribution Function Analysis.

Analysis of X-ray pair distribution function data has provided a detailed picture of the local structure of amorphous Zr(OH)4 and its thermal decomposition into ZrO2. In the untreated phase, the Zr atoms tend to be coordinated by six or seven oxygen atoms. The Zr centered polyhedra connect to each other primarily by sharing edges, but also with a significant amount of corner sharing, to form two-dimensional sheets in which the Zr are connected to an average of about five other Zr. This local structure is related to the structure of monoclinic ZrO2 and can be derived from it by removing certain Zr neighbors to form sheets and reduce the corner to edge sharing ratio. The maximum correlation length in Zr(OH)4 is about 12 Å. Heating up to 125 °C results in significant water loss but does not alter the network of Zr and bridging O atoms. Additional water loss caused by heating to 250 °C triggers a reorganization into a new type of amorphous phase with a three-dimensional network and a greater number of Zr-Zr neighbors. Further heating to 330 °C causes crystallization into a mixture of tetragonal and monoclinic ZrO2, with the minor tetragonal phase having a smaller average domain size. The tetragonal component vanishes by 900 °C.

Fast Oxidation of Porous Cu Induced by Nano-Twinning.

The fcc lattice of porous Cu prepared by dealloying Al2Cu with HCl aqueous solution exhibits a high density of twinning defects with an average domain size of about 3 nm along the ⟨111⟩ directions. The high density of twinning was verified by X-ray diffraction and qualitatively interpreted by a structural model showing the 5% probability of twinning defect formation. Most of the twinning defects disappeared after annealing at 873 K for 24 h. Twinned Cu reveals much faster oxidation rate in comparison to that without (or with much fewer) twinning defects, as shown by X-ray diffraction and hydrogen differential scanning calorimetry. Using ab initio DFT calculations, we demonstrate that twinning defects in porous Cu are able to form nucleation centers for the growth of Cu2O. The geometry of the V-shaped edges on the twinned {211} surfaces is favorable for formation of the basic structural elements of Cu2O. The fast oxidation of porous Cu prepared by dealloying can thus be explained by the fast formation of the Cu2O nucleation centers and their high density.

Understanding self ion damage in FCC Ni-Cr-Fe based alloy using X-ray diffraction techniques

Using X-ray diffraction line profile analysis (XRDLPA) approach the radiation response of FCC Ni-Cr-Fe based alloy 690 to 1.5 and 3 MeV Ni2+ ion damage was quantified in terms of its microstructural parameters. These microstructural parameters viz. average domain size, microstrain and dislocation density were found to vary anisotropically with fluence. The anisotropic behaviour is mainly attributable to presence of twins in pre-irradiated microstructure. After irradiation, surface roughness increases as a function of fluence attributable to change in surface and sub-surface morphology caused by displacement cascade, defects and sputtered atoms created by incident energetic ion. The radiation hardening in case of 1.5 MeV Ni2+ irradiated specimens too is a consequence of the increase in dislocation density formed by interaction of radiation induced defects with pre-existing dislocations. At highest fluence there is an initiation of saturation.

Investigation of secondary phase separation and mechanical properties of epoxy SBS-modified asphalts

Styrene-butadiene-styrene triblock copolymer (SBS) and epoxy resin have been widely applied in asphalt modification. In the present work, industrial SBS-modified asphalt (SBA) was used to prepare epoxy SBS-modified asphalt (ESBA). The morphology, rheological, thermal and mechanical properties of ESBAs were characterized. LSCM observations revealed that the formation of phase-separated microstructures between epoxy and SBA in ESBAs. Secondary phase separation occurred in epoxy asphalts (EAs) with 50 and 60 wt% asphalts. The phase inversion occurred in epoxy asphalt with 60 wt% asphalt. In addition, the morphology of ESBAs also exhibited secondary phase separation. Two interlocked continuous phases appeared in SBA domains of ESBA with 40 wt% SBA. No phase inversion was observed in ESBA with 60 wt% SBA. The presence of SBS decreased the average size of dispersed domains in EA. The existence of SBS increased the initial viscosity of the epoxy asphalt during cure reaction. The viscosity of ESBA was low enough to satisfy the requirement for the pavement of steel bridge decks. The thermal stability of EA was enhanced with the existence of SBS. Furthermore, the presence of SBS significantly improved mechanical properties of the epoxy asphalt. Especially, the tensile strength, elongation at break and toughness of ESBA containing 60 wt% SBA were 125%, 55% and 113% higher than those of the epoxy asphalt with the same content of asphalt.

Nanosized tetragonal β-FeSe phase obtained by mechanical alloying: structural, microstructural, magnetic and electrical characterization.

Nanocrystalline tetragonal β-FeSe phase was prepared mechanochemically using ball milling procedures in an inert atmosphere, starting from FexSe powder mixtures with x = 1.00, 1.25 and 1.50, with x = 1.25 and 1.50 leading to more than 93% of pure phase after annealing at 400 °C for 1 hour under vacuum. X-ray powder diffraction provides information on phase formation and phase transitions with milling time and temperature. The Rietveld method was used to refine the crystal structure, including the z coordinate of Se and occupancies, to determine the microstructure and to assess the amount of contaminant phases observed. Lattice contraction is found in the ab-plane more than along the c-axis, the small average size of crystalline domains (<22 nm) and the high microstrain (>1%) indicate the formation of highly strained nanoparticles. Magnetic and electrical characterization showed a poor superconductivity at 4 K and semiconducting properties only for thermally treated samples. These observations are explained by the presence of ferromagnetic impurity phases (residual Fe, hexagonal δ-FeSe phase and monoclinic Fe3Se4), but other effects caused by the mechanochemical synthesis must be considered, such as small average size, large/non-uniform size distribution and high microstrain of the nanosized tetragonal β-FeSe phase. The increase of the β-FeSe phase content with increasing storage time (ageing) above a few days to months in air, at RT and in the dark was observed for all as-milled samples. Preliminary data on the ageing effect are shown while a systematic study on this is in progress and will be presented elsewhere.

Green Chemistry Based Synthesis of Silver Nanoparticles from Floral Extract of Nelumbo Nucifera

In this study, silver nanoparticles were synthesized using an aqueous floral extract of Nelumbonucifera. The aqueous silver ions when subjected to flower extract were reduced due to bio-reduction and ensued in green synthesis of silver nanoparticles. The synthesized silver nanoparticles were manifested by a color change from colorless to reddish brown after the introduction of floral extract of N. nucifera. The characterizations of synthesized silver nanoparticles were done using UV/Vis spectroscopy, X-ray diffraction (XRD) and FTIR (Fourier transform infra-red) spectroscopy. UV/Vis spectrum results of silver nanoparticles showed peaks on the excitation plasmon resonance (SPR) band for wavelength of 450 nm. The face centered cubic (FCC) crystalline structure of the silver nanoparticles was committed by XRD. It also revealed the average domain size of synthesized silver nanoparticles as 90 nm.FTIR spectrum unfolded the existence of phytochemicals in N. nucifera extract which assisted bio-reduction. The experimentation concludes that for the synthesis of zero-valent silver nanoparticles, aqueous floral extract of N. nucifera could be employed as a reductant due to the presence of biomolecules. This simple, cost-effective and eco-friendly route for the synthesis of silver nanoparticles can be validated to be an alternative method to other physical and chemical reduction methods.

Chemical vapor deposition growth of scalable monolayer polycrystalline graphene films with millimeter-sized domains

The preparation of scalable graphene films has attracted an enormous attention due to its industrial importance for graphene applications. Here we present a synthesis method of high-quality continuous monolayer graphene films with millimeter-sized domains on ordinary Cu substrates using oxygen-assisted chemical vapor deposition. This method demonstrates a significantly improvement to the resultant graphene such as a largely decreased nucleation density from ∼106 to ∼101 nuclei/cm2, an increased average domain size from ∼0.004 to ∼1.5 mm and a film coverage from 64% to 100%. We attributed the success of this growth to the surface layer formed by bonded oxygen in Cu, which provides a higher priority for catalyzing the nucleation and growth of graphene domains.

Ptychographic X-Ray Imaging of Colloidal Crystals.

Ptychographic coherent X-ray imaging is applied to obtain a projection of the electron density of colloidal crystals, which are promising nanoscale materials for optoelectronic applications and important model systems. Using the incident X-ray wavefield reconstructed by mixed states approach, a high resolution and high contrast image of the colloidal crystal structure is obtained by ptychography. The reconstructed colloidal crystal reveals domain structure with an average domain size of about 2 µm. Comparison of the domains formed by the basic close-packed structures, allows us to conclude on the absence of pure hexagonal close-packed domains and confirms the presence of random hexagonal close-packed layers with predominantly face-centered cubic structure within the analyzed part of the colloidal crystal film. The ptychography reconstruction shows that the final structure is complicated and may contain partial dislocations leading to a variation of the stacking sequence in the lateral direction. As such in this work, X-ray ptychography is extended to high resolution imaging of crystalline samples.

Microstructural characterization of limestone exposed to heat with XRD, SEM and TG-DSC

Limestone is a common rock used in many buildings and found in underground engineering projects. After exposure to heat, for example, the occurrence of fires, the stability of limestone structures is mostly affected, which may have safety repercussions. Therefore, the impact of thermal effects on the microstructure of limestone is investigated in this study, in which 8 groups of limestone samples are exposed to different temperatures (25°C, 100°C, 200°C, 300°C, 500°C, 600°C, 700°C and 800°C), after which X-ray diffraction, differential scanning calorimetry and scanning electron microscopy are carried out. The mineral composition and the microstructure of the samples are numerically modeled, in which the diffraction peaks, full width at half maximum, integral breadth, microstrain, average domain size and dislocation density are analyzed. The macroscopic properties obtained from the results in other works in the literature including porosity, compressive strength, damage coefficients and modulus of elasticity are also compared with the parameters above. The changes in the crystal structure of two minerals, calcite and dolomite, are found to be anisotropic in the different crystal plane directions. It is also found that the limestone microstructure affects the macroscopic properties. A temperature between 200°C to 300°C is the critical temperature at which both the macroscopic properties and macrostructure demonstrate significant changes.

Universality of domain growth in antiferromagnets with spin-exchange kinetics.

We study phase ordering kinetics in symmetric and asymmetric binary mixtures, undergoing an order-disorder transition below the critical temperature. Microscopically, we model the kinetics via the antiferromagnetic Ising model with Kawasaki spin-exchange kinetics. This conserves the composition while the order parameter (staggered magnetization) is not conserved. The order-parameter correlation function and structure factor show dynamical scaling, and the scaling functions are independent of the mixture composition. The average domain size shows a power-law growth: [Formula: see text]. The asymptotic growth regime has [Formula: see text], though there can be prolonged transients with [Formula: see text] for asymmetric mixtures. Our unambiguous observation of the asymptotic universal regime is facilitated by using an accelerated Monte Carlo technique. We also obtain the coarse-grained free energy from the Hamiltonian, as a function of two order parameters. The evolution of these order parameters is modeled by using Model C kinetics. As for the microscopic dynamics, the average domain size of the nonconserved order-parameter (staggered magnetization) field exhibits a power-law growth: [Formula: see text] at later times, irrespective of the mean value of the conserved order-parameter (composition) field.

The scaling features of the 3D organization of chromosomes are highlighted by a transformation à la Kadanoff of Hi-C data

Technologies such as Hi-C and GAM have revealed that chromosomes are not randomly folded into the nucleus of cells, but are composed by a sequence of contact domains (TADs), each typically 0.5 Mb long. However, the larger scale organization of the genome remains still not well understood. To investigate the scaling behaviour of chromosome folding, here we apply an approach à la Kadanoff, inspired by the Renormalization Group theory, to Hi-C interaction data, across different cell types and chromosomes. We find that the genome is characterized by complex scaling features, where the average size of contact domains exhibits a power-law behaviour with the rescaling level. That is compatible with the existence of contact domains extending across length scales up to chromosomal sizes. The scaling exponent is statistically indistinguishable among the different murine cell types analysed. These results point toward a scenario of a universal higher-order spatial architecture of the genome, which could reflect fundamental, organizational principles.

Crystallization of hard segments in MDI/BD-based polyurethanes deformed at elevated temperature and their dependence on the MDI/BD content

Morphological variation of thermoplastic polyurethanes (TPUs) with different hard segment contents (HSCs) stretched at 100 °C higher than the Tg of hard domain was monitored by in-situ wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) techniques. WAXS patterns reveal that the crystalline modification of TPUs with high HSCs transforms from paracrystal (termed as form I) to form III of 4,4′-methylene diphenyl diisocyanate/1,4-butanediol (MDI/BD) segment, and TPUs with low HSCs show the direct transition from amorphous MDI/BD packing to form III packing. The form III crystals are fibrillar hard domains. Chord distribution functions (CDFs) computed from the SAXS patterns were employed to illustrate the domain topology. The streak-like CDF peaks off the meridian indicate the existence of cylindrical microfibrils which are composed of very low inhomogeneities between the destructured hard domains and stretched soft domains along the straining direction. These microfibrils of TPUs with low HSCs present a periodically lateral correlation. Interface distribution function (IDF) and chord length distribution (CLD) were computed from Bonart's longitudinal and transverse projection to quantify the domain stacking and microfibril arrangement respectively. The average size of hard domains increases up to a constant size with the increasing macroscopic strain which may be related to the maximal sequence length of hard segment. The average size of soft domain also reaches up to a constant size at large strain that is smaller than the fully-extended length of soft segment. The variation of domain size is different from deformation at room temperature. The HSC affects the behaviors of morphological evolution significantly.

Growth of NaO2 in Highly Efficient Na–O2 Batteries Revealed by Synchrotron In Operando X-ray Diffraction

The development of Na–O2 batteries requires understanding the formation of reaction products, as different groups reported compounds such as sodium peroxide, sodium superoxide, and hydrated sodium peroxide as the main discharge products. In this study, we used in operando synchrotron radiation powder X-ray diffraction (SR-PXD) to (i) quantitatively track the formation of NaO2 in Na–O2 cells and (ii) measure how the growth of crystalline NaO2 is influenced by the choice of electrolyte salt. The results reveal that the discharge could be divided into two time regions and that the formation of NaO2 during the major part of the discharge reaction is highly efficient. The findings indicate that the cell with NaOTf salt exhibited higher capacity than the cell with NaPF6 salt, whereas the average domain size of NaO2 particles decreases during the discharge. This fundamental insight brings new information on the working mechanism of Na–O2 batteries.

Nanoscale Morphology of Doctor Bladed versus Spin‐Coated Organic Photovoltaic Films

AbstractRecent advances in efficiency of organic photovoltaics are driven by judicious selection of processing conditions that result in a “desired” morphology. An important theme of morphology research is quantifying the effect of processing conditions on morphology and relating it to device efficiency. State‐of‐the‐art morphology quantification methods provide film‐averaged or 2D‐projected features that only indirectly correlate with performance, making causal reasoning nontrivial. Accessing the 3D distribution of material, however, provides a means of directly mapping processing to performance. In this paper, two recently developed techniques are integrated—reconstruction of 3D morphology and subsequent conversion into intuitive morphology descriptors —to comprehensively image and quantify morphology. These techniques are applied on films generated by doctor blading and spin coating, additionally investigating the effect of thermal annealing. It is found that morphology of all samples exhibits very high connectivity to electrodes. Not surprisingly, thermal annealing consistently increases the average domain size in the samples, aiding exciton generation. Furthermore, annealing also improves the balance of interfaces, enhancing exciton dissociation. A comparison of morphology descriptors impacting each stage of photophysics (exciton generation, dissociation, and charge transport) reveals that spin‐annealed sample exhibits superior morphology‐based performance indicators. This suggests substantial room for improvement of blade‐based methods (process optimization) for morphology tuning to enhance performance of large area devices.

Development of Au/CuO nanoplasmonic thin films for sensing applications

Nanocomposite thin films, containing Au nanoparticles dispersed in a CuO matrix, were prepared by reactive DC magnetron sputtering and post-deposition thermal annealing. The CuO matrix was found to be stoichiometric and the atomic concentration of Au was determined to be about 12.3at.%. After the annealing process, the average size of the crystalline domains of the Au nanoparticles (fcc structure) increased from about 6nm (at an annealing temperature of 300°C) to approximately 13nm (after annealing at 800°C), with a progressive crystallization of the CuO matrix in the monoclinic structure. A nanoplasmonic effect due to the localized surface plasmon resonance (LSPR) phenomenon appeared in the films after annealing temperatures of 400°C and higher. The correspondent LSPR bands appeared in the visible range of the transmittance spectra, becoming progressively narrower. Angle Resolved X-ray Photoelectron Spectroscopy results indicated that the surface of Au/CuO nanocomposite thin film is contaminated with a sub-nanometric layer (~0.6nm) of hydrocarbons and that the Au nanoparticles are relatively homogenously dispersed inside the CuO dielectric matrix. Furthermore, the results seem also to indicate that the Au nanoparticles are covered with about 0.2nm of CuO. Although further studies need to be performed to make clear the particular features of the present nanocomposite thin films' system, this work shows promising results concerning some particular applications that are envisaged, namely their use as LSPR sensing platforms for particular molecules detection (e.g. gases).