Preparation and properties of amorphous titania-coated zinc oxide nanoparticles

Amorphous TiO₂-coated ZnO nanoparticles were prepared by the solvothermal synthesis of ZnO nanoparticles in ethanol and the followed by sol-gel coating of TiO₂ nanolayer. The analyses of X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the resultant ZnO nanoparticles were hexagonal with a wurtzite structure and a mean diameter of about 60 nm. Also, after TiO₂ coating, the TEM images clearly indicated the darker ZnO nanoparticles being surrounded by the lighter amorphous TiO₂ layers. The zeta potential analysis revealed the pH dependence of zeta potentials for ZnO nanoparticles shifted completely to that for TiO₂ nanoparticles after TiO₂ coating, confirming the formation of core-shell structure and suggesting the coating of TiO₂ was achieved via the adhesion of the hydrolyzed species Ti-O⁻ to the positively charged surface of ZnO nanoparticles. Furthermore, the analyses of Fourier transform infrared (FTIR) and Raman spectra were also conducted to confirm that amorphous TiO₂ were indeed coated on the surface of ZnO nanoparticles. In addition, the analyses of ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectra revealed that the absorbance of amorphous TiO₂-coated ZnO nanoparticles at 375 nm gradually decreased with an increase in the Ti/Zn molar ratio and the time for TiO₂ coating, and the emission intensity of ZnO cores could be significantly enhanced by the amorphous TiO₂ shell.     

Surface structural evolution in iron oxide thin films

Ordered iron oxide ultrathin films were fabricated on a single-crystal Mo(110) substrate under ultrahigh vacuum conditions by either depositing Fe in ambient oxygen or oxidizing preprepared Fe(110) films. The surface structure and electronic structure of the iron oxide films were investigated by various surface analytical techniques. The results indicate surface structural transformations from metastable FeO(111) and O-terminated Fe(2)O(3)(0001) to Fe(3)O(4)(111) films, respectively. The former depends strongly on the oxygen pressure and substrate temperature, and the latter relies mostly upon the annealing temperature. Our experimental observations are helpful in understanding the mechanisms of surface structural evolution in iron oxides. The model surfaces of Fe-oxide films, particularly O-terminated surfaces, can be used for further investigation in chemical reactions (e.g., in catalysis).     

Mixed Co/Fe oxide nanoparticles in block copolymer micelles

Small iron oxide and Co-doped iron oxide nanoparticles (NPs) were synthesized in a commercial amphiphilic block copolymer, poly(ethylene oxide)-b-poly(methacrylic acid) (PEO 68-b-PMAA8), in aqueous solutions. The structure and composition of the micelles containing guest molecules (metal salts) or NPs (metal oxides) were studied using transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, and X-ray powder diffraction. The enlarged micelle cores after incorporation of metal salts are believed to be formed by both PMAA blocks containing metal species and penetrating PEO chains. The nanoparticle size distributions in PEO 68-b-PMAA8 were determined using small-angle X-ray scattering (SAXS) in bulk. Two independent methods for SAXS data interpretation for comprehensive analysis of volume distributions of metal oxide NPs showed presence of both small particles and larger entities containing metal species which are ascribed to organization of block copolymer micelles in bulk. The magnetometry measurements revealed that the NPs are superparamagnetic and their characteristics depend on the method of the NP synthesis. The important advantage of the PEO 68-b-PMAA8 stabilized magnetic nanoparticles described in this paper is their remarkable solubility and stability in water and buffers.     

Synthesis and electrorheological properties of oxalate group-modified amorphous titanium oxide nanoparticles

A kind of titanium oxide nanoparticles modified with varying amounts of oxalate group was prepared using a modified hydrolysis method. The microstructure, dielectric properties, and electrorheological (ER) performance were investigated. The results indicate that the oxalate group can effectively improve the dielectric properties and surface polarizability of the particles, and the ER performance of modified titanium oxide-based ER fluid is much higher than that of pure titanium oxide-based ER fluid. The shear stress of suitable oxalate group-modified amorphous titanium oxide-based ER fluid with a volume fraction of 30% reaches 47.5 kPa at E = 5 kV/mm, and the current density is less than 18 μAcm⁻². The yield stress can be up to 114 kPa at E = 5 kV/mm with a volume fraction of 40%.     

Investigation of structural relaxation of Fe85B15 amorphous metallic alloy by thermomagnetization

Thermomagnetometry was used to determine the Curie temperature of Fe₈₅B₁₅ amorphous alloy. Measurements were made with a TGS-1 Perkin-Elmer thermobalance in a permanent magnetic field. Armosphous material with a thickness of 25 m was prepared by melt spinning.In the temperature region 300 to 800 K the sample is characterized by one Curie transformation in the amorphous matrix atT _c570 K. A broad region of primary crystallization of -Fe begins at approximately 660 K, followed closely by the rapid crystallization of Fe₃B phase with maximum atT _cr2 750 K. Amorphous material which is unstable due to quenching is relaxed by annealing. The structural relaxation causes ageing of the Curie temperature in the metallic glass.The observed phenomena might be explained in terms of certain changes in local atomic arrangement.

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Zusammenfassung Die thermomagnetometrische Methode wurde zur Bestimmung der Curie-Temperatur der amorphen Legierung Fe₈₅B₁₅ herangezogen. Die Messungen wurden mit einer Perkin-Elmer-Thermowaage des Typs TGS-1 unter Anwendung eines permanenten Magnetfeldes ausgeführt. Das 25 m dicke amorphe Material wurde nach dem Schmelzspinnverfahren dargestellt. Im Temperaturbereich von 300 bis 800 K ist für die Probe eine Curie-Transformation in der amorphen Matrix beiT _c570 K charakteristisch. Ein breiter Bereich der primÄren Kristallisation von -Fe beginnt bei etwa 660 K, dem sofort eine schnelle Kristallisation der Fe₃B-Phase mit maximaler Geschwindigkeit beiT _cr2 750 K folgt. Die durch Abschrecken eintretende InstabilitÄt des amorphen Materials wird durch Tempern aufgehoben. Die strukturelle Relaxation verursacht eine Alterung der Curie-Temperatur im metallischen Glas. Die beobachteten PhÄnomene können durch VerÄnderungen der lokalen Anordnung der Atome erklÄrt werden

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Fe₈₅B₁₅. -1 -, . 25 . 300–800 . -Fe 660 , Fe₃B T _cr2750 . , , . . .

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We wish to thank P. Duhaj for the preparation of glassy ribbons.     

Electron-beam-induced topographical, chemical, and structural patterning of amorphous titanium oxide films

Electrolytically deposited amorphous TiO2 films on steel are remarkably sensitive to electron beam (e-beam) irradiation at moderate energies at 20 keV, resulting in controlled local oxide reduction and crystallization, opening the possibility for local topographical, chemical, and structural modifications within a biocompatible, amorphous, and semiconducting matrix. The sensitivity is shown to vary significantly with the annealing temperature of as-deposited films. Well-defined irradiation conditions in terms of probe current IP (5 microA) and beam size were achieved with an electron probe microanalyzer. As shown by atomic force and optical microscopy, micro-Raman spectroscopy, wavelength-dispersive X-ray (WDX), and Auger analyses, e-beam exposure below 1 Acm-2 immediately leads to electron-stimulated oxygen desorption, resulting in a well-defined volume loss primarily limited to the irradiated zone under the electron probe and in a blue color shift in this zone because of the presence of Ti2O3. Irradiation at 5 Acm(-2) (IP = 5 microA) results in local crystallization into anatase phase within 1 s of exposure and in reduction to TiO after an extended exposure of 60 s. Further reduction to the metallic state could be observed after 60 s of exposure at approximately 160 Acm(-2). The local reduction could be qualitatively sensed with WDX analysis and Auger line scans. An estimation of the film temperature in the beam center indicates that crystallization occurs at less than 150 degrees C, well below the atmospheric crystallization temperature of the present films. The high e-beam sensitivity in combination with the well-defined volume loss from oxygen desorption allows for precise electron lithographic topographical patterning of the present oxides. Irradiation effects leading to the observed reduction and crystallization phenomena under moderate electron energies are discussed.     

Phase diagram and structural evolution of Ag-Au bimetallic nanoparticles: molecular dynamics simulations

We studied the structural evolution of a 270-atom Ag-Au bimetallic nanoparticle (2 nm in size) with varying composition and temperature. The liquid to solid transition region and the solid-state structure were investigated using molecular dynamics simulations. To determine the exact transition temperature region, we applied the mean square displacement and structure deviation methods, as well as the generally used caloric curve of potential energy versus temperature. The results showed that a complete solid-solution phase diagram of the binary Ag-Au system was obtained. Irrespective of the composition, the freezing temperature of a Ag-Au bimetallic nanoparticle was lower than that of the bulk state by a margin of several hundred degrees, and three different solid-state structures are proposed in relation to the Au composition. Our phase diagram offers guidance for the application of Ag-Au nanoparticles.     

Revealing the composition-dependent structural evolution fundamentals of bimetallic nanoparticles through an inter-particle alloying reaction

Alloy nanoparticles represent one of the most important metal materials, finding increasing applications in diverse fields of catalysis, biomedicine, and nano-optics. However, the structural evolution of bimetallic nanoparticles in their full composition spectrum has been rarely explored at the molecular and atomic levels, imparting inherent difficulties to establish a reliable structure–property relationship in practical applications. Here, through an inter-particle reaction between [Au₄₄(SR)₂₆]²⁻ and [Ag₄₄(SR)₃₀]⁴⁻ nanoparticles or nanoclusters (NCs), which possess the same number of metal atoms, but different atomic packing structures, we reveal the composition-dependent structural evolution of alloy NCs in the alloying process at the molecular and atomic levels. In particular, an inter-cluster reaction can produce three sets of Au_xAg_44−x NCs in a wide composition range, and the structure of Au_xAg_44−x NCs evolves from Ag-rich [Au_xAg_44−x(SR)₃₀]⁴⁻ (x = 1–12), to evenly mixed [Au_xAg_44−x(SR)₂₇]³⁻ (x = 19–24), and finally to Au-rich [Au_xAg_44−x(SR)₂₆]²⁻ (x = 40–43) NCs, with the increase of the Au/Ag atomic ratio in the NC composition. In addition, leveraging on real-time electrospray ionization mass spectrometry (ESI-MS), we reveal the different inter-cluster reaction mechanisms for the alloying process in the sub-3-nm regime, including partial decomposition–reconstruction and metal exchange reactions. The molecular-level inter-cluster reaction demonstrated in this study provides a fine chemistry to customize the composition and structure of bimetallic NCs in their full alloy composition spectrum, which will greatly increase the acceptance of bimetallic NCs in both basic and applied research.

An inter-particle reaction between atomically precise [Au₄₄(SR)₂₆]²⁻ (SR = thiolate) and [Ag₄₄(SR)₃₀]⁴⁻ nanoparticles reveals the composition-dependent structural evolution of alloy Au_xAg_44−x nanoparticles at the atomic level.     

The structural characteristics of amorphous silicas

The structural characteristics of amorphous silicas obtained from aqueous solutions of sodium silicate and serpentinite and kaolin minerals were studied by X-ray diffraction and differential thermal analysis. Siloxane groups of amorphous SiO₂ were found to contain Si-O bonds different in saturation.     

Nickel oxide nanoparticles prepared by gelatin and their application toward the oxygen evolution reaction

Green synthesis of pure nickel oxide nanoparticles (nano-NiO) in aqueous medium has been carried out using gelatin. The particles have been characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDAX). Gelatin plays an important role in the formation of the nano-NiO. TEM image shows the formation of nano-NiO with average particle size 16 nm, which agrees well with the XRD data. Moreover, efficient and stable nano-NiO-based anodes were fabricated by casting of the nano-NiO and multi-walled carbon nanotube solution (NiO-MWNT) on glassy carbon (NiO-MWNT/GC), platine (NiO-MWNT/Pt), and carbon paste (NiO-MWNT/CP) electrodes. The electrocatalysis of oxygen evolution reaction (OER) at modified electrodes has been examined using linear scanning voltammetry (LSV). The OER is significantly enhanced upon modification of the electrodes with NiO-MWNT, as demonstrated by a negative shift in the LSV curves at the NiO-MWNT-modified electrodes compared to that obtained at the unmodified ones. The maximum electrocatalytic activity toward the OER was obtained in alkaline media. The values of energy saving of oxygen gas at a current density of 5 mA cm^?2 Pt, CP, and GC electrodes are 14.1, 16.0, and 21.6 kW h kg^?1, respectively. The low cost as well as the marked stability of the modified electrodes makes them promising candidates in industrial water electrolysis process.     

Visualization of deformation-induced structural rearrangements in amorphous polymers

A technique is proposed for decorating amorphous polymers: Before the deformation (shrinkage) of an amorphous polymer, its surface is decorated with a thin metal coating. The subsequent deformation is accompanied by surface structure formation, which makes the processes that occur in the polymer visible. The proposed technique makes it possible to visualize and describe the mechanism of transfer of the polymer from the surface into the bulk and vice versa and to obtain direct information about the direction of the actual local stress. The technique makes it possible to obtain information about the topological heterogeneity of rubber networks, to reveal the features of structural rearrangements that occur during the cold rolling of amorphous polymers, and to describe the phenomenon of self-elongation during annealing of the oriented PET. These microscopic data explain the following features of the structural and mechanical behavior of glassy polymers from a unified viewpoint: stress relaxation in a polymer in the elastic (Hookean) region of the stress-strain curve, an increase in stress in a deformed glassy polymer during its isometric annealing below T _g, the low-temperature shrinkage of a deformed polymer glass in the strain range below its yield point, the storage of internal energy in a deformed glassy polymer in the strain range below the yield point, some anomalies of thermophysical properties, and some other features.     

Surface-stabilized amorphous germanium nanoparticles for lithium-storage material

Amorphous Ge nanoparticles with the particle size of approximately 10 nm were prepared by capping butyl groups and were characterized using XAS, TEM, FT-IR reflectance, and electrochemical cycling. The XAS results for the first-cycle Ge nanoparticles exhibited either a little particle aggregation after reformation of the Ge-Ge metallic bond or reformation of Ge-Ge metallic bond followed by a little particle aggregation. More interestingly, butyl groups, being electrochemically stable, remained after cycling, and the quantum mechanical calculation of the thermodynamic energy of the reaction using the GAMESS (General Atomic and Molecular Electronic Structure System) program suggested the formation of a very stable surface Ge-C bond that cannot be easily subjected to the subsequent chemical reactions. Initial charge capacity is 1470 mAh/g with an irreversible capacity ratio of 12%; no capacity fading was observed out to 30 cycles. Even at 5 C rate discharging, capacity retention was 98%, compared to that at 0.2 C rate discharging. In addition, the capacity was fully recovered at 0.2 C rate cycling.     

Phosphorized zirconium oxide nanoparticles

In this work a simple method to phosphorize the surface of nanometric particles of crystalline zirconia is described. The reaction rate of phosphorization was regulated by adding acetic acid and the observed particle size was in the range 40–60 nm. A proton conductivity of the order of 10^?3 S cm^?1 was measured for phosphorized nanoparticle powder mixed with micro‐fine teflon powder (3:1) at room temperature. Phosphorized nanoparticles are stable when dispersed in acetic acid and are suitable for composite material preparation. Copyright © 2005 John Wiley & Sons, Ltd.     

Mechanisms of lithium transport in amorphous polyethylene oxide

We report calculations using a previously reported model of lithium perchlorate in polyethylene oxide in order to understand the mechanism of lithium transport in these systems. Using an algorithm suggested by Voter, we find results for the diffusion rate which are quite close to experimental values. By analysis of the individual events in which large lithium motions occur during short times, we find that no single type of rearrangement of the lithium environment characterizes these events. We estimate the free energies of the lithium ion as a function of position during these events by calculation of potentials of mean force and thus derive an approximate map of the free energy as a function of lithium position during these events. The results are consistent with a Marcus-like picture in which the system slowly climbs a free energy barrier dominated by rearrangement of the polymer around the lithium ions, after which the lithium moves very quickly to a new position. Reducing the torsion forces in the model causes the diffusion rates to increase.     

Modelling of nano-alloying and structural evolution of bimetallic core-shell nanoparticles obtained via the microemulsion route

A Monte Carlo model has been developed to describe the formation of bimetallic nanoparticles via the microemulsion route. The motivation stems from the need to understand the kinetics of nanoparticle formation in microemulsion droplets in order to determine the best experimental conditions to synthesize a nanoparticle with a given structure. We focus our study on the influence of the homogeneous and heterogeneous critical nucleus sizes of both metals on nanoparticle structure, as well as the role played by the surfactant film flexibility. The study reveals that the final structure is sensitive to changes in the critical nucleus numbers, because these parameters determine the rate of nucleation. An increase in the difference between nucleation rates of both metals gives rise to a better segregation of metals in the final nanoparticle. Likewise, as long as the formation of heterogeneous seeds is faster, the degree of alloying is greater. Finally, a fast material intermicellar exchange leads to a better mixture of metals, so the influence of the critical nucleus sizes on nanoparticle structure becomes less pronounced as the flexibility of surfactant film is increased.     

Normal structural bonding and defects in covalent amorphous solids

Although the 8-N rule of covalent bonding is generally obeyed in amorphous semiconductors, well-defined defect centers exist and these control the electronic properties of the solids. The defects have two distinct reasons for their presence—they can arise from either strains upon material preparation or thermodynamic considerations. The strain-related defects characterize those amorphous solids in which the average coordination number is larger than approximately 2.4; their concentration is ordinarily very sensitive to the preparation techniques. In contrast, thermodynamically induced defects arise because of their low creation energy, and a minimum concentration characterizes any given material. These ideas have led to a resolution of several major puzzles with regard to the electronic properties of the two major classes of amorphous semiconductors—chalcogenide glasses and amorphous silicon-based alloys. Pure amorphous silicon is overconstrained and has large defect densities, but these can be reduced by many orders of magnitude if the material is alloyed with monovalent atoms such as hydrogen or fluorine. On the other hand, amorphous As₂Se₃ always contains a high defect density, for thermodynamic reasons. In addition to the concentration of defects present in a given material, its electronic properties depend critically also on the nature of these defects. In particular, the sign of the effective correlation energy of the defect with the lowest creation energy is of the utmost importance.     

Effects of slight Fe (III)-doping on structural and optical properties of TiO2 nanoparticles

Journal of Sol-Gel Science and Technology - In this research work, undoped and slight Fe-doped-TiO2 nanoparticles (Fe–TiO2 NPs) were prepared using simple chemical sol–gel method and...     

Molecular dynamics simulation of amorphous SiO2 nanoparticles

Molecular dynamics simulation of amorphous SiO2 spherical nanoparticles has been carried out in a model with different sizes, 2, 4, and 6 nm, under non-periodic boundary conditions. We use the pair interatomic potentials which have weak Coulomb interaction and Morse type short-range interaction. Models have been obtained by cooling from the melt via molecular dynamics (MD) simulation. Structural properties of amorphous nanoparticles obtained at 350 K have been studied via partial radial distribution functions (PRDFs), mean interatomic distances, coordination numbers, and bond-angle distributions, which are compared with those observed in the bulk. Calculations of the radial density profile in nanoparticles show the tendency of oxygen to concentrate at the surface as observed previously in other amorphous clusters or thin films. Size effects on structure of nanosized models are significant. The calculations show that if the size is larger than 4 nm, amorphous SiO2 nanoparticles have a distorted tetrahedral network structure with the mean coordination number ZSi-O approximately 4.0 and ZO-Si approximately 2.0 like those observed in the bulk. Surface structure, surface energy, and glass transition temperature of SiO2 nanoparticles have been obtained and presented.     

Tensile deformation induced structural rearrangement in amorphous silicon nitride

Silicon nitride exhibits good mechanical properties and thermal stability at high temperatures. Since experiments have limitations in nanoscale characterization of the chemical structure and related properties, atomistic simulation is a proper way to investigate the mechanism of this unique feature. In this paper, the melt-quench method is used to generate the amorphous structure of silicon nitride; then the structural properties of silicon nitride under tensile deformation were studied by angular pair distribution functions. The corresponding mechanism of tensile stress induced structure rearrangement is explored.