Synthesis of silver-coated magnetite nanoparticles

In this paper we describe the preparation of relatively monodisperse silver-coated Fe₃O₄ nanoparticles by a two-step procedure. Fe₃O₄ nanoparticles of 9 ± 2 nm in size were first prepared in microemulsions. They were subsequently coated with silver using glucose as reducing agent. The presence of a relatively homogeneous coating of ≈2 nm was confirmed by transmission electron microscopy and X-ray diffraction. A preliminary study of the magnetic properties shows a large decrease of the magnetization for the coated magnetite nanoparticles in comparison with the uncoated ones.     

On temperature variation of oxygen parameter for magnetite nanoparticles

The Mössbauer spectra of ⁵⁷Fe nuclei for magnetite nanoparticles have been studied. It is established that the oxygen parameter u changes by a value of about 0.002 with the temperature increase in the range 100–300 K. The u values are obtained from the shifts of partial spectra corresponding to the Fe³⁺ ions in both tetrahedral and octahedral positions. The “covalence effects” are calculated by the molecular orbitals method.     

A new approach to diffusion-like relaxation processes

We measured the time decay of the electric field in two dielectric non-crystalline solids and the data were analyzed in the framework of a new theoretical approach. It is observed that the application of this approach allows identifying different regimes in the relaxation process. At long times the dynamics end up by following a power law decay, which suggests the existence of a scale property in the interaction that defines the state of the materials and also the possibility of defining an invariant. We check the stability of this invariant under different time intervals, which means also a low dependence of it on noisy data.     

Synthesis and in vitro evaluation of toxicity of silica-coated magnetite nanoparticles

Magnetic iron oxide nanoparticles properly coated with silica may be interesting in molecular biology, particularly as an auxiliary diagnostic material in biomedicine. This paper describes the coating of superparamagnetic magnetite nanoparticles with amorphous silica by sol–gel process using tetraethoxysilane. The physical–chemical characterization of the magnetite powder before and after silica-coating was performed by X-ray diffraction, Fourier-transform infrared, and zeta potential. The in vitro biocompatibility of the samples was analyzed by the viability/proliferation and collagen secretion capability of incubated osteoblasts in the presence of the composites. In summary, it was demonstrated that osteoblast viability decreased to about 20% in the presence of silica-coated magnetite nanoparticles when compared to the control group result. Moreover, the silica-coated magnetite nanoparticles did not alter osteoblast collagen secretion. The in vitro preliminary evaluation showed that silica-coating magnetite nanoparticles did not produce any severe alteration in biocompatibility. Further investigations are required to better understand the biocompatibility of silica-coated magnetite nanoparticles in biomedical applications.     

Use of different rapid mixing devices for controlling the properties of magnetite nanoparticles produced by precipitation

Magnetite nanoparticles were precipitated by the classic Massart's method in a 2.5 L stirred tank reactor where the injection of reagent solutions was effectuated by different micro-mixers (T-tube and Hartridge-Roughton rapid mixing devices). The specific surface area, the average particle size and the particle size distribution were highly influenced by changing operating parameters. Laser Diffraction, BET adsorption, Energy-Dispersive X-ray Spectroscopy (EDX), Raman spectroscopy and Transmission Electron Microscopy (TEM) were used for characterizing magnetite nanoparticles. Especially, Hartridge-Roughton micromixer appears to be the most efficient mixing device for producing magnetite nanoparticles. The average particle size of magnetite nanoparticles prepared by Hartridge-Roughton rapid mixing device was less than 10 nm and the EDX and Raman spectroscopy shows that the particle purity is quite high.     

Silicate nanoparticles by bioleaching of glass and modification of the glass surface

Bioleaching is examined as a low temperature (50 °C) soft chemical approach to nanosynthesis and surface processing. We demonstrate that fungus based bioleaching of borosilicate glass enables synthesis of nearly monodispersed ultrafine (∼5 ± 0.5 nm) silicate nanoparticles. Using various techniques such as X-ray diffraction, X-ray photoelectron spectroscopy and FTIR we compare the constitution and composition of the nanoparticles with that of the parent glass, and establish the basic similarities between the two. The bioleaching process is shown to enhance the non-bridging oxygen component and correspondingly influence the Si-O-Si network. The root mean square roughness of glass surface is seen to increase from 1.27 nm for bare glass to 2.52 nm for 15 h fungal processed case, this increase being equivalent to that for glass annealed at 500 °C.     

A possible new approach to the better understanding of crystallization kinetics

Literature data dealing with the structure of solutions, solubility of tiny particles, and the organization of small colloidal particles in solutions were summarized to support the evidence that the growth units in the crystallization by precipitation are identical with clusters or primary particles. These growth units may self-organize themselves in a kind of a three-dimensional network surrounding the growing crystals or secondary particles. This colloidal concept was used to explain qualitatively some experimental facts observed in the controlled double jet precipitation of sparingly soluble salts.     

Size modification of Au nanoparticles induced by slow highly charged ions 40Arq+ irradiation

Size modification of Au nanoparticles (NPs), deposited on the Au-thick film surface and irradiated by slow highly charged ions (SHCI) ⁴⁰Ar^q+ (3 ? q ? 12) with fixed low dose of 4.3 × 10¹¹ ions/cm² and various energy ranging from 74.64 to 290.64 keV at room temperature (293.15 K), was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The effect of projectile kinetic energy on the modified size of NPs was explored by an appropriate choice of the fixed process parameters such as ion flux, irradiation temperature, incident angle, irradiation time, etc. The morphological changes of NPs were interpreted by models involving collisional mixing, Ostwald ripening (OR) and inverse Ostwald ripening (IOR) of spherical NPs on a substrate. A critical kinetic energy as well as a critical potential energy of the projectile in the Au NPs size modification process were observed.     

Hydrogen embrittlement assisted by ball-milling to obtain AlCuFe nanoparticles

In this work, we show that the synthesis of AlCuFe nanoparticles can be achieved by a wet ball-milling process. The AlCuFe intermetallic system is highly sensitive to the environmental embrittlement mechanism. Taking advantage of this, the wet ball-milling was used to increase the rate of grinding and accelerate the characteristic cleavage fracture of these phases. This research was carried out by subjecting Al₆₄Cu₂₄Fe₁₂ pre-alloyed ribbons to high-energy ball-milling under different powder–humidity relationships. The pre-alloyed and milled powders were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and scanning transmission electron microscopy (STEM). High resolution electron microscopy (HREM) measurements and energy-dispersive X-ray spectroscopy (EDXS) elemental chemical mapping confirm that the nanoparticles have a BCC structure with Al–Cu–Fe chemical composition. During the wet ball-milling, the aluminum content in the ψ-phase diminishes due to embrittlement mechanism which provokes its aperiodic disarrangement. This aluminum loss could be related with a ψ–β transformation.     

Preparation of polyelectrolyte microcapsules with silver and gold nanoparticles in a shell and the remote destruction of microcapsules under laser irradiation

A number of methods are proposed for encapsulating silver and gold nanoparticles into shells of polyelectrolyte microcapsules for the purpose of increasing the sensitivity of microcapsules to laser radiation. It is shown that capsules with nanocomposite shells can be remotely damaged under laser radiation with different powers and wavelengths. The sensitivity of capsules with silver and gold nanoparticles in shells to this radiation can be controlled by varying the conditions used for the preparation of the capsules. The release of the encapsulated material under laser radiation makes these systems promising for use as microcontainers intended for the target delivery of drugs in an organism.     

A new approach to thin film crystal silicon on glass: Biaxially-textured silicon on foreign template layers

We propose a new approach to growing photovoltaic-quality crystal silicon films on glass. Other approaches to film Si focus on increasing grain size in order to reduce the deleterious effects of grain boundaries. Instead, we propose aligning the silicon grains biaxially (both in and out of plane) so that (1) grain boundaries are ‘low-angle’ and have less effect on the electronic properties of the material and (2) subsequent epitaxial thickening is simplified. They key to our approach is the use of a foreign template layer that can be grown with biaxial texture directly on glass by a technique such as ion-beam-assisted deposition or inclined substrate deposition. After deposition of the template layer, silicon is then grown aligned to the template and subsequently thickened. Here, we outline this new approach to silicon on glass, describe initial experimental results and discuss challenges that must be overcome.     

A variational approach to cellular crystal growth

The variational method is applied to the study of crystal growth from melt under the condition that the boundary between the liquid and solid phases has a cellular structure. The surface energy of the interface is taken into account.     

A new approach of creating Au‐Sn solder bumps from electroplating

A homogeneous melting eutectic Au/Sn solder bump for laser chip application has been developed. The under‐bump metallization consists of a Ni wetting layer, a plating seed layer of Pt/Au/Ti multi‐layer scheme. The solder is electroplated as a sequence of Ni, Au and Sn layers. The bump can be exposed to multi‐step reflow cycles. The reflow of the solder as plated starts with a phase forming process in the solid state which results in an eutectic‐like phase and the near eutectic dand z phases. The dand z phases dissolve during the liquid state stage of the reflow at temperatures between 300 and 350 °C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Surface modification and grafting of carbon fibers: A route to better interface

This review is an audit of various Carbon fibers (CF) surface modification techniques that have been attempted and which produced results with an enhancement in the interfacial characteristics of CFRP systems. An introduction to the CF surface morphology, various techniques of modifications, their results and challenges are discussed here. CFs are emerging as the most promising materials for designing many technologically significant materials for current and future generations. In order to extract all the physic-mechanical properties of CF, it is essential to modulate a suitable environment through which good interfacial relation is achieved between the CF and the matrix. The interface has the utmost significance in composites and hybrid materials since tension at the interface can result in a deterioration of the fundamental properties. This review is aimed to provide a detailed understanding of the CF structure, its possible ways of modification, and the influence of interfacial compatibility in physic-mechanical and tribological properties. Both physical and chemical modifications are illustrated with specific examples, in addition to the characterization methods. Overall, this article provides key information about the CF based composite fabrication and their many applications in aerospace and electronics- where light weight and excellent mechanical strength are required.     

A novel approach to Au@SiO2 core-shell spheres

A novel synthesis method was described to prepare Au@SiO₂ core-shell spheres, using a commercial gold colloid and tetraethyl orthosilicate as the precursors. The synthesis concept was based on surface modification of the gold nanoparticles with a binary system of surfactants, or using both of 2-Mercapto-ethanol and (3-Aminopropyl)-trimethoxysilane together, and the Stöber processing. The shape and size, and silica coatings of the resultant particles were investigated by transmitting electron microscopy (TEM). The Au@silica core-shell spheres, each containing a single gold nanoparticle or an aggregate of several gold nanoparticles at the center, could be prepared.     

A facile direct deposition of silver nanoparticles on silicon surface by silver mirror process

The Ag nanoparticles with different morphology are directly prepared on Si surface by a facile silver mirror reaction without capping agents and shape‐controlling seeds. Ag nanoplates and Ag polyhedrons are produced on the Si surface by controlling the reaction temperature. Ag nanoplates are easily obtained at the low temperature, which are the products controlled by kinetics pathway. Ag polyhedrons are produced at the high temperature under the combined action of the surface energy and strain energy. Through the catalysis of Ag nanoplates and Ag polyhedrons, different nanoporous structures on the Si surface are obtained using the same etching process, which are useful for the antireflection layers in solar‐cell devices.     

Microstructural modification of chalcogenide glasses by femtosecond laser

With the irradiation by femtosecond (fs) laser with high repetition rate, GeS₂ micro/nano-crystalline formation and microstructural modification occurred in pseudo-binary GeS₂–In₂S₃ glass, while almost no similar change was observed in GeS₂ glass. The addition of In₂S₃ is beneficial for the precipitation of GeS₂ micro/nano-crystals. It is expected that functional micro/nano-crystals can be controllably prepared in chalcogenide glasses by fs laser irradiation through glass composition design.     

Highly swellable sol–gels prepared by chemical modification of silanol groups prior to drying

Sol–gel materials that swell six times their dried volume when placed in organic solvents were prepared using the bridged silsesquioxane bis(trimethoxysilyethyl)benzene through base catalysis by tetrabutyl ammonium fluoride. Prior to drying the gels, water and catalyst were rinsed from the solvated matrix and residual silanol groups were derivatized with a chlorosilane (R–Si(CH₃)₂Cl). The swelling behavior was completely reversible when the materials are dried at elevated temperature. Swelling is highly dependent on the processing conditions, including the choice of solvent and catalyst. There is no preferential adsorption of solute molecules to swelled sol–gels despite the diversity of chlorosilanes used to derivatize the materials.