Formation Of Nucleation Centers Research Articles

Chemical Modification of Glycoproteins' Carbohydrate Moiety as a General Strategy for the Synthesis of Efficient Biocatalysts by Biomimetic Mineralization: The Case of Glucose Oxidase.

Zeolitic imidazolate framework-8 (ZIF-8) is widely used as a protective coating to encapsulate proteins via biomimetic mineralization. The formation of nucleation centers and further biocomposite crystal growth is entirely governed by the pure electrostatic interactions between the protein’s surface and the positively charged Zn(II) metal ions. It was previously shown that enhancing these electrostatic interactions by a chemical modification of surface amino acid residues can lead to a rapid biocomposite crystal formation. However, a chemical modification of carbohydrate components by periodate oxidation for glycoproteins can serve as an alternative strategy. In the present study, an industrially important enzyme glucose oxidase (GOx) was selected as a model system. Periodate oxidation of GOx by 2.5 mM sodium periodate increased negative charge on the enzyme molecule, from −10.2 to −36.9 mV, as shown by zeta potential measurements and native PAGE electrophoresis. Biomineralization experiments with oxidized GOx resulted in higher specific activity, effectiveness factor, and higher thermostability of the ZIF-8 biocomposites. Periodate oxidation of carbohydrate components for glycoproteins can serve as a facile and general method for facilitating the biomimetic mineralization of other industrially relevant glycoproteins.

Modified co-precipitation process effects on the structural and magnetic properties of Mn- doped nickel ferrite nanoparticles

Manganese doped Nickel ferrites nanoparticles (NPs) have been synthesized by modified co-precipitation method for investigating the effects of adding dopant ions after formation of nucleation centers in the reaction medium. The structure and magnetic properties of the as-synthesized samples have been studied by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR) and Vibrating sample magnetometer (VSM). The structural results showed that all the samples have cubic spinel phase with the average 21 nm crystallite size. In addition, variation of the preferred XRD peak from (311) orientation to (440) occurred because of the compressive strain in the structure which was calculated by means of Williamson-Hall method (W–H). Adding dopant ions, after nucleation, caused strain, spin canting and reduction of saturation magnetization.

Fine Grain Concrete on Mixing Water Activated in Cavitation Permanent Magnet-Type Apparatus

The authors obtained fine grain concrete based on the mortars of additives-electrolytes undergone mechanic magnetic activation and characterized by improved compression and bending strength and enhanced freeze-thaw resistance. There was investigated the impact of mechanic magnetic activation (MMA) on mixing water when adding calcium chloride and sodium thiosulphate as well as on porosity of cement stone and specific features of phase formation in cement stone. It was stated by the authors that MMA facilitates formation of nucleation centers in activated water in the presence of additives-electrolytes, optimization of porous space as well as crystallization of calcium carbonate in the form of aragonite when lowering the content of Portlandite. The mechanism of joined influence of hydrodynamic and magnetic treatment of mixing water has been determined.

Anodes for Li-ion batteries based on p-Si with self-organized macropores

The practical application of microstructured anodes produced by the electrochemical etching of single-crystal silicon is limited by their cost. The proposed approach will make it possible to reduce the cost for several reasons: less stringent requirements to the quality of the initial material due to the replacement of n-Si with p-Si, the exclusion of operations that are aimed at the formation of nucleation centers, and the repeated use of a silicon substrate. The formation of random macropores in 10–20 Ω cm p-Si (100) in a 4% solution of hydrofluoric acid in dimethylformamide is studied and the role of chemical etching is revealed. The dependences on the current density are obtained for the etching rate, morphology of the porous layers, effective valence, pore density, and average pore diameter. The part played by chemical dissolution in the electrolyte is determined. A technology is developed for the deposition of 50-μ-thick porous layers. This technology combines successive detachments of several membranes from the same substrate and provides enhanced porosity (~70%). The electrochemical characteristics of anodes formed from these membranes are examined, and 120+ test cycles are performed in the mode with the charge capacity limited to 1000 mA h/g at a current of 0.2 A/g.

In situ crystallization of metallic glasses during magnetic field annealing

The impact of an external magnetic field upon changes in the crystallization kinetics of Fe90Zr7B3 metallic glass is studied by in situ nuclear forward scattering (NFS) of synchrotron radiation. Structural and magnetic information on the whole process of nanograin formation is monitored on fly in real time by means of time domain Mössbauer effect technique. Isothermal annealing performed at 753K under weak magnetic field (Bext=0.652T) exhibits more rapid crystallization in comparison with zero-field conditions. These surprising effects of an external magnetic field upon the process of phase transformation are attributed to energetic perturbations of magnetic interactions in comparison with the thermal energy. Consequently, the formation of nucleation centers is enhanced. Such accelerated crystallization was not reported so far for metallic glasses exposed to magnetic field during annealing. The influence of magnetic field on the resulting properties is usually assessed under static conditions after annealing. The use of NFS with rapid data acquisition has allowed in situ observation of the microstructure development throughout the fast annealing processes. In this way, not only the starting and the final stages of the structure can be characterized but also the intermediate transition period states of the transformation can be followed to fine details.

Three‐Dimensional Silver Nanoparticle Formation Using Femtosecond Laser Irradiation in Phosphate Glasses: Analogy with Photography

Three‐dimensional patterning of metal–dielectric composites is achieved at the sub‐micrometer scale in glass. A high silver‐content zinc‐phosphate optical transparent glass is structured by means of a near‐infrared femtosecond laser via non‐linear absorption processes. The silver ions embedded in glass photochemically react under controlled laser irradiation, inducing ion clustering and the formation of nucleation centers. A subsequent thermal development causes silver reduction and growth into metallic nanoparticles. A very strong surface plasmon resonance is measured, revealing the very high concentration of metallic particles. The direct laser writing process enables inscriptions of silver nanoparticle domains well below the diffraction limit (∼100 nm). A very detailed parametric study is given, leading to the first thorough understanding of the ultrafast laser‐induced photochemistry in silver‐containing glass materials. These nanostructures are considered promising candidates for the design of highly efficient sensing devices via plasmonics and, beyond that, for photonics and metamaterials applications.

Structural state and mechanical properties of nanocrystalline carbon films obtained by methane pyrolysis in electric field

We describe a method of carbon film synthesis on single-crystalline silicon substrate, which is based on methane pyrolysis in electric field. The calculated values of pressures and temperatures developed during the bombardment of substrates by C4− carbon ions in the course of pyrolysis amount to P ∼ 1.3 GPa and T ∼ 2300 K, respectively. These conditions lead to the formation of nucleation centers that are necessary for the growth of carbon film. Measurements show that the microhardness of obtained carbon films reaches 60–80% of the hardness of natural diamond. The structural state of the film material was studied by X-ray diffraction, electron microscopy, and atomic force microscopy. It is established that the synthesized films represent a composite material with a carbon matrix containing nanodimensional inclusions of another phase.

Deformation-twinning-related features of primary recrystallization of (110)[001] single crystals of the Fe-3% Si-0.5% Cu alloy

In the regions of the deformed cube-on-edge single crystal of the Fe-3% Si-0.5% Cu alloy with an enhanced density of deformation twins, the nucleation of new grains during primary recrystallization (PR) occurs via several mechanisms. The majority of nuclei of PR are formed on twins as on substrates. The newly formed grains of PR are characterized by the presence of a cube-on-edge texture and are in special misorientations of the Σ3 type with respect to the twin orientation and of the Σ9 (Σ27) type with respect to the octahedral matrix. The mechanism of the formation of nucleation centers for PR on the twins as on substrates can be a splitting of the nonequilibrium special boundary Σ3. A significant role of special misorientations in the formation of the Goss texture upon PR has been shown experimentally.

The formation of the developed nanorelief on deposited films

A model of a film nanorelief formed upon the deposition of atomic flow on the surface is proposed. This model is based on the growth of structures formed from single atoms diffusing on the surface. The complex fractal structure of the film appears due to the formation of stable clusters that either are a result of the fluctuation formation of nucleation centers with critical sizes or they form on additive atoms that serve as nucleation centers. At high temperatures, adatoms may be transferred to hotter relief elements due to the decreasing diffusion activation energy that goes along with the increasing temperature. This promotes the formation of the film’s fractal structure. At a later stage of fractal film growth, the main growth mechanism is the diffusion-limited aggregation of deposited atoms. The size of the minimal cluster of the fractal structure is determined by the diffusion smoothing; it is equal to rmin = 2σa3/T, where ρ is the surface tension, T is the surface temperature, and a is the atomic size.

Three-dimensional micromagnetic calculations for naturally shaped magnetite: Octahedra and magnetosomes

A three-dimensional micromagnetic algorithm for modelling naturally shaped particles is presented. It uses a FFT accelerated calculation of the demagnetizing energy. Exchange energy calculation directly takes into account the micromagnetic boundary condition. A rectangular grid enclosing the particle is chosen to economically fit the shape. After verifying that the new program reliably reproduces previous calculations, the program is used to determine room temperature magnetization structures and single domain to vortex transition sizes. These calculations are performed for octahedral magnetite and magnetosomes of different elongations. The least energy magnetization structures of octahedral particles are similar to the flower and vortex states found for cubic particles. The critical size d 0 above which an inhomogeneous magnetization structure has lower energy than the homogeneous flower state as well as the grain-size dependence of M rs/ M s, closely resemble cubic particles. However, meta-stable flower states persist up to much larger grain size in octahedral magnetite. This explains previous observations of large TRM/ARM peaks in hydrothermal magnetite. In realistic magnetosome geometries, the SD-PSD transition is shifted towards larger grain sizes as compared to previous estimates based on elongated rectangular grains. For substantially elongated grains, this is a result of the alignment of the particles' long edge with the crystallographic easy axis. For more equidimensional grains, the rounded ends of magnetosomes reduce spin deflection at the top and bottom edges. Thereby, the formation of nucleation centers is effectively inhibited even without additional stabilization by magnetostatic interaction within a magnetosome chain.

Kinetics of the solid-phase synthesis of mullite in the presence of topaz

Results of a kinetic study of solid-phase interactions in stoichiometric oxide mixtures of mullite composition are reported. The mechanism of mullitization, irrespective of the oxide form (crystalline or amorphous), is diffusive in character. Topaz added in small quantities accelerates the process through generating surface and structure imperfections and activating the diffusion of reactants owing to the assistance of gaseous fluorides released by topaz. The secondary mullite produced by thermal degradation of topaz facilitates the formation of nucleation centers for topochemical reactions and activates the mullite crystallization.

On the mechanism of the P2–Na 0.70CoO 2→O2–LiCoO 2 exchange reaction—Part II: an in situ X-ray diffraction study

A model was proposed to describe the exchange reaction of sodium by lithium in P2 crystals, it was based first on the formation of nucleation centers and then on the growth of O2 domains in P2 crystals from these nucleation centers. This study has shown that depending on the ratio between the growing and nucleation speeds, O2, O6 or faulted structures are obtained and that this model allows a good analysis of the exchange process. XRD patterns simulation and their comparison with that of experimental O2–LiCoO 2 have shown that there was almost no defects in the O2–LiCoO 2 structure obtained by ion exchange in water. Therefore, this study has shown that the growth of the O2 domains in the P2–Na 0.7CoO 2 crystals is faster than the formation of nucleation centers. This P2–Na 0.7CoO 2→O2–LiCoO 2 exchange reaction was also studied in situ by X-ray diffraction; simulations of key XRD patterns by P2–O2 intergrowths were also achieved. It was shown, in good agreement with the simulations, that the growth of O2 domains was faster than the formation of the nucleation centers and kinetically activated by a P2–Na 0.70CoO 2→P2 *–Na ∼0.50CoO 2 phase transition. For those reasons, the P2–Na 0.70CoO 2→O2–LiCoO 2 exchange reaction in water leads to an O2 phase, with an almost ideal packing.

On the mechanism of the P2–Na 0.70CoO 2→O2–LiCoO 2 exchange reaction—Part I: proposition of a model to describe the P2–O2 transition

A model was proposed to describe the exchange reaction of sodium by lithium in P2 crystals. The exchange consists on the formation of nucleation centers and then on the growth of O2 domains in P2 crystals from these nucleation centers. Octahedral environments for lithium ions are obtained when one slab over two glides by (2/3,1/3,0) or by (1/3,2/3,0) in P2 structure. The existence of two different gliding vectors should lead to stacking faulted structures that can be simulated using DIFFaX software. The comparison of simulated and experimental XRD patterns for O2–LiCoO 2 (ex-Na 0.7CoO 2) has shown that in that case the growth of the O2 domains in the P2 crystals is faster than the formation of nucleation centers.

Low-Temperature-Processed Polycrystalline silicon thin-film transistors Using a New Two-Step Crystallization Technique

Low-temperature-processed (LTP) Polycrystalline silicon thin-film transistors (poly-Si TFTs) fabricated with a poly-Si film crystallized by a new two-step crystallization (NTSC) technique were investigated. The NTSC is characterized by the combination of excimer-laser-induced formation of nucleation centers and short-time low- temperature furnace annealing to create clear crystalline grains with very few in-grain defects. The LTP poly-Si TFTs fabricated with a NTSC poly-Si film not only exhibit better performance but also significantly shorten the crystallization time (about 6 h at 600°C) as compared to those fabricated using conventional solid phase crystallization (about 20 h or longer at 600°C).

Influence of Metallic Surfaces and their Treatment on the Formation of Nucleation Centers

Influence of Metallic Surfaces and their Treatment on the Formation of Nucleation Centers