Mean Domain Size Research Articles

Correlative visible light and soft X-ray tomography of in-situ mesoscale heterochromatin organization.

Recent evidence has revealed that cellular aging is accompanied by alterations in DNA methylation and histone modifications leading to a decrease in nucleosome packing density and heterochromatin remodeling. While these observations were obtained with multi-omics data (eg. Hi-C, ATAC-seq), the underlying ultrastructural mechanisms of mesoscale heterochromatin reorganization during cellular aging are still unclear. Towards this, we developed correlative light microscopy and cryo-soft X-ray tomography to analyze the alterations in heterochromatin organization in human mammary fibroblast cells. Our analysis revealed the micro-domain organization of heterochromatin structure with the mean domain size of 115 nm in the intact and hydrated state of cells. Upon addition of histone deacetylase inhibitor, that phenocopied aging, we observed a marked decrease in the heterochromatin density distribution, disruption of microdomains, and decrease in chromatin compaction length scales. To validate these observations, we also developed a bidisperse copolymer model in a confined volume using Brownian dynamics simulations. Collectively, our results provide direct evidence of mesoscale domains in heterochromatin packing and their alterations during cellular aging

Weak boundary enabled tensile ductility in dealloyed porous Fe alloy

Dealloying has emerged as a new route to the synthesis of porous or nanoporous materials for a variety of novel structural/functional applications. However, dealloyed (nano-)porous metals are notoriously brittle and often fracture catastrophically in bending or tension, which is detrimental to their applications. In this paper, we report that under tension, the irreversible fracture strain (εi) of a macroscopic porous Fe(MnCr) alloy prepared by liquid metal dealloying can be enhanced from nearly zero to 4.1 % by introducing weak domain boundaries, while previous samples with homogeneous (nano-)porous structure usually fracture at εi below 1.0 %. Tensile ductility is enhanced only if the mean domain size (D¯) is not too much larger than mean ligament diameter (L¯), evidenced by the dramatic increase in εi as D¯/L¯ decreases from ∼24 to ∼7. The “ductile” deformation of these materials is associated with the diffuse failure under tension, arising from the promoted nucleation of micro-cracks and the crack deflection or branching along weak domain boundaries at lower D¯/L¯. This strategy might also apply to other (nano-)porous materials self-organized in dealloying or fabricated by other methods.

Antiferromagnetic Spin Orientation and Magnetic Domain Structure in Epitaxially Grown MnN Studied Using Optical Second-Harmonic Generation

$\mathrm{Mn}\mathrm{N}$ is a centrosymmetric collinear antiferromagnet belonging to the transition-metal-nitride family with a high N\'eel temperature ($660\phantom{\rule{0.2em}{0ex}}\mathrm{K}$), a low anisotropy field, and a large magnetic moment ($3.3{\ensuremath{\mu}}_{B}$ per $\mathrm{Mn}$ atom). Despite several recent experimental and theoretical studies, the spin symmetry (magnetic point group) and magnetic domain structure of the material remain unknown. In this work, we use optical second-harmonic generation (SHG) to study the magnetic structure of thin epitaxially grown single-crystal (001) $\mathrm{Mn}\mathrm{N}$ films. Our work shows that spin moments in $\mathrm{Mn}\mathrm{N}$ are tilted away from the [001] direction and the components of the spin moments in the (001) plane are aligned along one of the two possible in-plane symmetry axes ([100] or [110]), resulting in a magnetic-point-group symmetry of 2/m1'. Our work rules out magnetic-point-group symmetries 4/mmm1' and mmm1' that have been previously discussed in the literature. Four different spin domains consistent with the 2/m1' magnetic-point-group symmetry are possible in $\mathrm{Mn}\mathrm{N}$. A statistical model based on the observed variations in the polarization-dependent intensity of the second-harmonic signal collected over large sample areas puts an upper bound of $0.65\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{m}$ on the mean domain size. Our results show that SHG can be used to probe the magnetic order in metallic antiferromagnets. This work is expected to contribute to the recent efforts in using antiferromagnets for spintronic applications.

X-ray Line Profile Analysis of Austenitic Phase Transition and Morphology of Nickel-Free Fe-18Cr-18Mn Steel Powder Synthesized by Mechanical Alloying

In this study, microstructural evolution and phase transition of nickel-free Fe-18Cr-18Mn (wt. %) austenitic steel powders, induced by mechanical alloying, were investigated. X-ray diffraction, scanning electron microscopy, and microhardness testing techniques were used to observe the changes in the phase composition and particle size as functions of milling time. The first 30 h of mechanical alloying was performed in an argon atmosphere followed by nitrogen for up to 150 h. X-ray diffraction results revealed that the Fe-fcc phase started to form after 30 h of milling, and its fraction continued to increase with alloying time. However, even after 150 h of milling, weak Fe-bcc phase reflections were still detectable (~3.5 wt. %). Basic microstructure features of the multi-phase alloy were determined by X-ray profile analyses, using the whole powder pattern modeling approach to model anisotropic broadening of line profiles. It was demonstrated that the WPPM algorithm can be regarded as a powerful tool for characterizing microstructures even in more complicated multi-phase cases with overlapping reflections. Prolonging alloying time up to 150 h caused the evolution of the microstructure towards the nanocrystalline state with a mean domain size of 6 nm, accompanied by high densities of dislocations exceeding 1016/m2. Deformation-induced hardening was manifested macroscopically by a corresponding increase in microhardness to 1068 HV0.2. Additionally, diffraction data were processed by the modified Williamson–Hall method, which revealed similar trends of domain size evolutions, but yielded sizes twice as high compared to the WPPM method.

Dynamic scaling and stochastic fractal in nucleation and growth processes.

A class of nucleation and growth models of a stable phase is investigated for various different growth velocities. It is shown that for growth velocities v ≈ s ( t ) / t and v ≈ x / τ ( x ), where s ( t ) and τ are the mean domain size of the metastable phase (M-phase) and the mean nucleation time, respectively, the M-phase decays following a power law. Furthermore, snapshots at different time t that are taken to collect data for the distribution function c ( x , t ) of the domain size x of the M-phase are found to obey dynamic scaling. Using the idea of data-collapse, we show that each snapshot is a self-similar fractal. However, for v = const ., such as in the classical Kolmogorov-Johnson-Mehl-Avrami model, and for v ≈ 1 / t, the decays of the M-phase are exponential and they are not accompanied by dynamic scaling. We find a perfect agreement between numerical simulation and analytical results.

Highly Ordered and Dense Thermally Conductive Graphitic Films from a Graphene Oxide/Reduced Graphene Oxide Mixture

Summary We report a new approach to making highly dense, oriented, and crystalline graphite films from heat-treated and pressed graphene oxide (G-O). By introducing small-diameter reduced graphene oxide (rG-O) flakes into the graphene oxide starting material, we found that after heat treatment at 3,000°C, the sample density and atomic order substantially improved over a film composed, at the outset, only of pure G-O flakes. A subsequent mechanical press increased the density but reduced the atomic order. A second 3,000°C heat treatment restored the graphitic structure with graphitization metrics exceeding even those of the first heat treatment. The optimized graphitic film with an original concentration of 15 wt % reduced G-O in G-O gave well-oriented graphitic films with a density of 2.1 g cm−3, cross-plane thermal conductivity of 5.65 W m−1 K−1, and in-plane thermal conductivity of 2,025 ± 25 W m−1 K−1.

Effect of the Degree of Overcooling on Relaxation of the Domain Structure of Triglycine Sulphate

The formation and evolution of the domain structure in the vicinity of the Curie point is studied in triglycine sulfate crystals subjected to fast cooling TC. We derive an analytical expression for time dependence of the mean characteristic domain size. This expression enable us to investigate the process of enlargement of domain structure through all stages of its relaxation into a state of thermodynamic equilibrium. The model predicts a root-square behavior of the mean domain size, which agrees well with available experimental data. The rate of enlargement of the domain structure is shown to depend on the degree of overcooling. The time dependence of the mean domain size obtained in this study enables us to determine the radius of intermolecular interactions in the crystals under study.

An influence of vacancies and elastic deformation coupling onto phase decomposition of binary systems

We present a comprehensive study of phase decomposition of binary alloys by taking into account lattice mismatch, coupling of both solute and vacancy concentrations with elastic deformation and multiplicative noise satisfying fluctuation dissipation relation. We discuss scaling dynamics and universality of domain size growth. We verified numerically delaying dynamics of mean domain size growth caused by field dependent mobilities. It is shown that vacancy–deformation coupling leads to vacancies agglomeration in soft phase, it suppress phase decomposition at early stages and promotes an increase in the domain size at late stages.

Employing soft x-ray resonant magnetic scattering to study domain sizes and anisotropy in Co/Pd multilayers

It is demonstrated that the magnetic diffraction pattern of the isotropic disordered maze pattern is well described utilizing a gamma distribution of domain sizes in a one-dimensional model. From the analysis, the mean domain size and the shape parameter of the distribution are obtained. The model reveals an average domain size that is significantly different from the value that is determined from the peak position of the structure factor in reciprocal space. As a proof of principle, a wedge-shaped $({\mathrm{Co}}_{t\AA{}}/{\mathrm{Pd}}_{10\AA{}}{)}_{8}$ multilayer film, that covers the thickness range of the spin-reorientation transition, has been used. By means of soft x-ray resonant magnetic scattering (XRMS) and imaging techniques the thickness-driven evolution of the magnetic properties of the cobalt layers is explored. It is shown that minute changes of the domain pattern concerning domain size and geometry can be investigated and analyzed due to the high sensitivity and lateral resolution of the XRMS technique. The latter allows for the determination of the magnetic anisotropies of the cobalt layers within a thickness range of a few angstroms.

Crystallization kinetics of binary colloidal monolayers.

Experiments and simulations are used to study the kinetics of crystal growth in a mixture of magnetic and nonmagnetic particles suspended in ferrofluid. The growth process is quantified using both a bond order parameter and a mean domain size parameter. The largest single crystals obtained in experiments consist of approximately 1000 particles and form if the area fraction is held between 65-70% and the field strength is kept in the range of 8.5-10.5 Oe. Simulations indicate that much larger single crystals containing as many as 5000 particles can be obtained under impurity-free conditions within a few hours. If our simulations are modified to include impurity concentrations as small as 1-2%, then the results agree quantitatively with the experiments. These findings provide an important step toward developing strategies for growing single crystals that are large enough to enable follow-on investigations across many subdisciplines in condensed matter physics.

Influence of magnetic domain size on dipolar interactions and hysteresis field asymmetry in layered high/low coercivity perpendicular anisotropy systems

Dipolar interactions in low-coercivity/Pd/high-coercivity [Co/Pd]X/Pd/[Co/Pd]10 multilayer systems are studied as a function of the domain size in the [Co/Pd]X low-coercivity layer (LCL), while maintaining the domain size in the high-coercivity layer (HCL) constant. As the number of repeats X increases from 5 to 30, the mean domain size of the [Co/Pd]X LCL decreases from hundreds of micron to hundreds of nanometers. After demagnetization, different regimes can be distinguished from partial or exact domain duplication for LCL domain size larger than HCL one to uncorrelated behavior for much smaller LCL domains. The results obtained via magnetic force microscopy allow understanding the symmetry and asymmetry versus externally applied field as observed in macroscopic magnetometry measurements.

Fast and non-catalytic growth of transparent and conductive graphene-like carbon films on glass at low temperature

This article presents the synthesis and systematic study of graphene-like carbon thin films directly grown on commercial glass by using remote electron cyclotron resonance plasma-assisted chemical vapour deposition. The fabrication process is extremely rapid and performed on 2 inch scale dielectric substrate at relatively low temperature (<550 °C) without using metal catalyst. This method avoids damaging and expensive transfer processes of graphene based films and improves compatibility with current fabrication technologies. Nanostructural characterization by transmission electron microscopy indicates the formation of layered graphene-like carbon material. Raman spectroscopy shows that the film consists of nanocrystals with a mean domain size close to 2 nm, probably interconnected by amorphous material. These graphene-like carbon based films are transparent and conductive. Functional optoelectric characterization of these films confirms their high transparency over 95% and relative high conductivity around 5 kΩ, exceeding the properties of non-doped small domain graphene based films grown at low temperatures reported so far.

Size-Controlled Synthesis and Microstructure Investigation of Co3O4 Nanoparticles for Low-Temperature CO Oxidation

Noble-metal-free functional oxides are active catalysts for CO oxidation at low temperatures. Spinel-type cobalt oxide (Co3O4) nanoparticles can be easily synthesized by impregnation of activated carbon with concentrated cobalt nitrate and successive carbon burn off. Mean size and particle size distribution can be tuned by adding small amounts of silica to the carbon precursor, as witnessed by whole powder pattern modeling of the X-ray powder diffraction data. The catalytic tests performed after silica removal show a significant influence of the mean domain size and of size distribution on the CO oxidation activity of the individual Co3O4 specimens, whereas defects play a less important role in the present case.

Lipid-Protein Interactions Alter Line Tensions and Domain Size Distributions in Lung Surfactant Monolayers

The size distribution of domains in phase-separated lung surfactant monolayers influences monolayer viscoelasticity and compressibility which, in turn, influence monolayer collapse and set the compression at which the minimum surface tension is reached. The surfactant-specific protein SP-B decreases the mean domain size and polydispersity as shown by fluorescence microscopy. From the images, the line tension and dipole density difference are determined by comparing the measured size distributions with a theory derived by minimizing the free energy associated with the domain energy and mixing entropy. We find that SP-B increases the line tension, dipole density difference, and the compressibility modulus at surface pressures up to the squeeze-out pressure. The increase in line tension due to SP-B indicates the protein avoids domain boundaries due to its solubility in the more fluid regions of the film.

Growth of Few-Layer Graphene on Sapphire Substrates by Directly Depositing Carbon Atoms

Few-layer graphene (FLG) is successfully grown on sapphire substrates by directly depositing carbon atoms at the substrate temperature of 1300°C in a molecular beam epitaxy chamber. The reflection high energy diffraction, Raman spectroscopy and near-edge x-ray absorption fine structure are used to characterize the sample, which confirm the formation of graphene layers. The mean domain size of FLG is around 29.2 nm and the layer number is about 2–3. The results demonstrate that the grown FLG displays a turbostratic stacking structure similar to that of the FLG produced by annealing C-terminated α-SiC surface.

Relating domain size distribution to line tension and molecular dipole density in model cytoplasmic myelin lipid monolayers

We fit the size distribution of liquid-ordered (L(o)) domains measured from fluorescence images of model cytoplasmic myelin monolayers with an equilibrium thermodynamic expression that includes the competing effects of line tension, λ, dipole density difference, Δm, and the mixing entropy. From these fits, we extract the line tension, λ, and dipole density difference, Δm, between the L(o) and liquid-disordered (L(d)) phases. Both λ and Δm decrease with increasing surface pressure, , although λ/Δm(2) remains roughly constant as the monolayer approaches the miscibility surface pressure. As a result, the mean domain size changed little with surface pressure, although the polydispersity increased significantly. The most probable domain radius was significantly smaller than that predicted by the energy alone, showing that the mixing entropy promotes a greater number of smaller domains. Our results also explain why domain shapes are stable; at equilibrium, only a small fraction of the domains are large enough to undergo theoretically predicted shape fluctuations. Monolayers based on the composition of myelin from animals with experimental allergic encephalomyelitis had slightly lower values of λ and Δm, and a higher area fraction of domains, than control monolayers at all . While it is premature to generalize these results to myelin bilayers, our results show that the domain distribution in myelin may be an equilibrium effect and that subtle changes in surface pressure and composition can alter the distribution of material in the monolayer, which will likely also alter the interactions between monolayers important to the adhesion of the myelin sheath.

Adhesion property and morphology of styrene triblock/diblock copolymer blends

AbstractRelationship between adhesion properties and phase structures of styrene triblock and diblock copolymer blends was investigated in detail. For this purpose, polystyrene‐block‐polyisoprene‐block‐polystyrene triblock and polystyrene‐block‐polyisoprene diblock copolymers were used and the diblock content was varied from 0 to 100 wt %. All blends formed the sea‐island structure in which spherical polystyrene domains were dispersed in polyisoprene matrix and mean domain size was ∼ 20 nm. The domain size was slightly affected by the diblock content. The fracture stress and strain measured by a tensile test decreased and the molecular mobility measured by a 1H pulse nuclear magnetic resonance analysis increased with an increase of diblock content. The tack as adhesion property increased with an increase of diblock content below 70 wt %, then decreased over 70 wt %. The cohesive strength decreased and the interfacial adhesion increased with an increase of diblock content. The tack increases by the development of cohesive strength and interfacial adhesion. Therefore, the tack showed the maximum at the optimum contribution balance between cohesive strength and interfacial adhesion. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Diagenesis and Metamorphism of Triassic Flysch Along Profile Zoigê‐Lushan, Northwest Sichuan, China

AbstractWe used illite and chlorite crystallinities, index minerals, mineral assemblages, polytype and domain size of white mica, electron microprobe analysis (EMPA), b0 geobarometer and chlorite geothermometer to quantify the diagenetic and metamorphic overprint on the Triassic flysch formations in the Songpan‐Garzê orogen along profile Zoigê‐Lushan, northwest Sichuan. Two anchizones, two epizones, one diagenetic zone and a transition belt in‐between them are defined on the basis of the obtained data. Illite crystallinity correlates strongly with the best mean domain size of mica and moderately with chlorite crystallinity. 2M1 white mica polytype are observed within the epizone whilst 2M1 and 1M polytypes occur in the anchizone and diagenetic zone. Epizonal metamorphism reached maximum temperatures of 370°C±21°C at low‐to intermediate pressure conditions. Clay minerals underwent Ostwald ripening during metamorphism. Rocks from both sides of the Longmenshan fault reveal contrasting degrees of metamorphic overprint: on the northwest side of the Longmenshan fault, epimetamorphic conditions contrast with diagenetic rocks on the southeast side.

Phonon expansion and dispersion for material diagnosis in condensed matter channels

The “average acoustic pulse dispersion length in condensed matter channels” is expanded to show that propagating acoustic pulses may behave as phonons, which can be characterized and used to evaluate the channel through which they have travelled. Employing transducers, pulser/receivers and condensed matter channels, it is possible to generate and detect a ‘harmonic Gaussian’ pulse (i.e. a Gaussian pulse modulated by a phased carrier frequency). Propagating in the channel the pulse expands, its carrier frequency is diminished, but the harmonic Gaussian property stays. This parallels the quantum-mechanics ‘wave packet’ characterization, relating to such entities as ‘photons’ and ‘phonons’. Channel inhomogeneities affect travelling phonons. Application of nonlinear regression analysis to reflected echoes, at the front and back of the channel, uncovers intrinsic signal parameters. A theory provided relating the derived phonon profile change to average scattering length, mean domain size or defect spacing, g s, a material property. Experimental and analytical results provide g s estimates for diverse channels: a 10 mm column of glycerine, a 4.8 mm column of Elmer's glue and an 8 mm copper plate. The g s values agree with length scales in the materials (nanometres to microns) determined by other experiments, e.g. electron microscopy.

Effects of vibration force field on the interfacial interaction and morphology of polystyrene/poly(methyl methacrylate) blends

Immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends were extruded using an electromagnetic dynamic plasticating extruder. Effects of vibration force field on the interfacial interaction and morphology of PS/PMMA blends were studied by differential scanning calorimetry (DSC), IR spectra, scanning electron microscope (SEM) and small angle X-ray scattering (SAXS). Results show that the introduction of a vibration force field into the extrusion process increases the solubility of the two components of PS/PMMA blends, which seems to be a physical compatibilization as indicated by the IR spectra. The enhanced interfacial interaction and the increased shear effect caused by vibration improve the dispersion of the dispersed phase. With application of vibration, the PS/PMMA blends exhibit a smaller drop size and a narrower particle size distribution. The morphologies of PS/PMMA blends with different compositions have a different response to vibration forces; the mean domain size of 25/75 PS/PMMA blends has a higher speed of decrease with increase of vibration amplitude or frequency. The Porod invariant data as determined by SAXS indicate that introduction of vibration improves the homogeneity of the PS/PMMA system.