bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface-Sandwich Segregation Phenomena in Bimetallic Ag-Ni and Pd-Ni Nanoparticles: A Molecular Dynamics Study
Authors: Levchenko Elena V. , Evteev Alexander V. , Belova Irina V. , Murch Graeme E.
Published: September 2009

By molecular dynamics simulation it is shown that interdiffusion in the initial f.c.c. Ag-core ( 28 at. %) – Ni-shell ( 72 at. %) and Ni-core ( 34 at. %) – Pd-shell ( 66 at. %) nanoparticles can lead to surface–sandwich segregation. It is observed that there is a separation of the initial Ag-Ni core-shell structure into Ag-core – Ni-intermediate shell – Ag-disperse surface monolayer. The initial crystal Ni-Pd core-shell structure transforms to the core of a non-crystalline Pd-rich solid solution with quite strongly developed icosahedral short-range order, which is covered by a surface–sandwich shell, where Ni atoms are located in the centres of interpenetrating icosahedra of a subsurface Kagomé net layer while the Pd atoms occupy the vertices of the icosahedra and cover this Ni layer from inside and outside. We demonstrate that under certain conditions a surface–sandwich segregation phenomenon at the nanoscale can be observed in systems with completely different phase diagrams in the bulk states: in systems displaying the extremely low mutual solubility as in the Ag-Ni system, or in systems exhibiting a continuous mutual solid solubility like the Pd-Ni system.
Composition Effect on Shrinkage of Hollow Binary Alloy Nanospheres
Authors: Evteev Alexander V. , Levchenko Elena V. , Belova Irina V. , Murch Graeme E.
Published: September 2009

In this paper, a hollow random binary alloy nanosphere and initially homogeneous is considered under the approximation that the radial dependence of the vacancy formation free energy can be neglected. On the basis of a theoretical description and kinetic Monte Carlo simulations it is shown that the steady-state condition for the atomic components is not achievable during its shrinkage at any composition when the ratio of the tracer diffusion coefficients is not greater than two orders of magnitude. In the theoretical description, the dependence of the collapse time of the hollow random binary alloy nanosphere on the atomic fraction of the faster diffusing species at can be estimated by using the geometric mean of the ratios of the atomic fluxes at self-diffusion and steady-state. At the ratio of the atomic fluxes approaches the self-diffusion ratio as increases.
Shrinkage of Hollow Nanoparticles of Oxides of Cu and Ni at High Temperatures
Authors: Nakamura Ryusuke , Nakajima Hideo , Mori Hirotaro
Published: September 2009

The structural stability of hollow Cu2O and NiO nanoparticles, which were obtained via oxidation of Cu and Ni nanoparticles in air, was studied by transmission electron microscopy (TEM). Hollow Cu2O and NiO were observed to have shrunk at 473 and 623 K in annealing under 5.0×10-5 Pa, respectively, where the reduction reactions from oxides to metals started. As a result of shrinking associated with reduction, hollow oxides turned into solid metal nanoparticles after annealing at higher temperatures for a long time. In addition, hollow oxides shrunk and collapsed through high-temperature oxidation. It was found that shrinking of hollow oxides during oxidation occurs at temperature where the diffusion coefficients of slower diffusing species reach around 10-22 m2s-1. It seems that the hollow oxide nanoparticles tend to shrink and collapse at high temperatures because the hollow structures are energetically unstable.
Essay on Techniques & Physics of Some Diffusion-Controlled Processes in Materials: Relevance to Nanofabrication Applications
Authors: Nechaev Yuriy S. , Öchsner Andreas
Published: September 2009

An annotated analytical essay of possible nanofabrication and nanotechnology applications is presented with respect to: (1) some techniques and original results [1-4] concerning the regularities and micromechanisms (physics) of the hydrogen fluoride gas activator influence on the diffusion-controlled oxidation processes of titanium, zirconium and zirconium-based alloys with niobium, and also – on nitriding, boriding and carbiding a series of refractory metals (Ti, Zr, Nb, Mo, W, Ta); (2) some techniques, original results and physics of the diffusion-controlled formation processes of the compound-like nanosegregation [5-13] and the results [13-23] on the liquid-like phase at grain boundary regions in metals and alloys. In the scope of this review, a constructive analysis, the Arrhenius-type treatment, and the original data interpretation [16-21] has been carried out for the first time; (3) some techniques, original analytical results, and physics [24, 25] of the diffusion-controlled processes of the hydrogen multilayer intercalation (physisorption of a condensation or clustering type) with carbonaceous nanostructures. The main objective of the given analytical essay is to attract the researchers’ attention to the expediency of such a non-conventional data analysis and interpretation.
Diffusion in Isotope Heterostructures Investigated by Neutron Reflectometry
Authors: Hüger Erwin , Stahn Jochen , Geckle Udo , Bruns Michael , Schmidt Harald
Published: September 2009

Studies of self-diffusion in solids are presented, which are based on neutron reflectometry. For the application of this technique the samples under investigation are prepared in form of isotope heterostructures. These are nanometer sized thin films, which are chemically completely homogenous, but isotope modulated. Using this method, diffusion lengths in the order of 1 nm and below can be detected which allows to determine ultra low diffusivities in the order of 10-25 m2/s. For the model system amorphous silicon nitride we demonstrate how the structure of the isotope hetrostructures (triple layers or multilayers) influences the efficiency of diffusivity determination.
Solute Diffusion in Grain Boundaries – Outside the Scope of Fisher Model
Authors: Rodin Alexey , Klinger Leonid , Bokstein Boris S.
Published: September 2009

Thermodynamic and kinetic models are developed for grain boundary segregation and diffusion with regards to the possible complexes formation in grain boundary. The equilibrium state for ideal solutions can be described by the equilibrium constants b and K. The first corresponds to the pure segregation, i.e. the exchange A and B atoms between grain boundary and the bulk. The second represents the equilibrium of the reaction of the complexes formation in grain boundary. The segregation isotherm and diffusion profiles are calculated. It is shown that both b and K equilibrium constants define completely dependence of the total grain boundary concentration of B atoms on the bulk concentration and distribution of B atoms between two states: free (pure exchange) and tied (in the complexes). Segregation in both forms (free B atoms and tied B atoms) decreases grain boundary diffusivity in comparison with the absence of segregation.
Jump Frequencies of Cd Tracer Atoms in L12 Lanthanide Gallides
Authors: Jiang Xia , Zacate Matthew O. , Collins Gary Scott
Published: September 2009

Jump frequencies of Cd tracer atoms were measured in three lanthanide gallides having the L12 structure: DyGa3, ErGa3 and LuGa3. 111In/Cd impurity probe atoms were observed to occupy the non-cubic Ga-sites through the nuclear quadrupole interaction using the method of perturbed angular correlation of gamma rays (PAC). Measurements at elevated temperatures exhibited nuclear relaxation (damping) of quadrupolar perturbation functions attributed to diffusional jumps of the probes among orientationally inequivalent Ga-sites. Accurate values of jump frequencies were determined from fits of the measured perturbation functions using a model of stochastically fluctuating electric-field gradients, as in previous work [e.g., Matthew O. Zacate, Aurélie Favrot and Gary S. Collins: Physical Review Letters Vol. 92 (2004) p. 225901]. Arrhenius plots of jump frequencies for the three systems exhibited jump-frequency activation enthalpies in the range 0.86-1.05 eV and prefactors of about 2 THz. The activation enthalpy for ErGa3, 0.86(2) eV is compared with those for ErAl3, 1.40(4) eV, and ErIn3, 1.34(5) eV.
Following the First Steps of UV Degradation of High Density Polyethylene by Fluorescence Spectroscopy
Authors: Douminge Ludovic , Mallarino S. , Feaugas X. , Bernard J.
Published: September 2009

Ultraviolet radiation is one of the major factors that affect weathering of polymers. Indeed, diffusion of oxygen containing groups [-C-O, C=O and C(=O)O-] into the molecular chains of polymers is particularly enhanced by UV irradiation in air, thus entailing structural and chemical changes such as polymeric chain breaking, cross-linking and oxidation. The goal of this study is to predict the photo-chemical ageing of polymers upon UV radiation through a non destructive method: fluorescence spectroscopy. In the case of high density polyethylene (HDPE) the addition of fluorophore is required to make it fluorescent. The spectral features of fluorescence are very sensitive to the interactions between the excited molecules and the matrix. In this way, Fourier-Transform InfraRed spectrophotometry (FTIR) and Differential Scanning calorimetry (DSC) have been employed to correlate the fluorescence spectra with the degradation phenomena.
First-Principle Calculation of Monovacancy and Divacancy Interactions with Atomic Oxygen in Nickel: Thermal Expansion Effects
Authors: Mijoule Claude , Megchiche El Hocine , Andrieu Eric , Monceau Daniel
Published: September 2009

The insertion and diffusion energies of oxygen in presence of vacancies in nickel are studied by using the first-principle projector augmented waves (PAW). When the oxygen atom is located in a substitution site, the formation of a vacancy-oxygen pair is observed. Furthermore, we show that the formation of divacancies allows the oxygen atom to migrate more easily in the metal. A model for the migration process of the three-defect system is proposed. Finally, thermal expansion effects are included in our study; it is shown that temperature effects emphasize the diffusion.
Motion of Cadmium Tracer Atoms in Al11R3 Phases (R=La,Ce,Pr)
Authors: Lage Stephanie , Collins Gary Scott
Published: September 2009

Jump frequencies of Cd tracer atoms were measured in three phases having the orthorhombic Al11R3 structure, with R= La, Ce, or Pr. The structure has four inequivalent Al-sites and two inequivalent R-sites. 111In/Cd tracer atoms were observed to occupy several sites via the nuclear quadrupole interaction using perturbed angular correlation of gamma rays (PAC). Time-domain PAC spectra became damped as the temperature increased, which is attributed to nuclear relaxation caused by diffusional jumps of Cd tracer atoms leading to changes in orientations and/or magnitudes of electric field gradients (EFG’s). Maximum relaxations were observed near 770 K. A method is proposed for estimating the mean jump frequency at that temperature, giving a mean jump frequency w averaged over all sites of about 100 MHz. At still higher temperatures, damping decreased due to motional averaging, and the quadrupole perturbations evolved into unique signals having lower frequencies and corresponding in each phase to the averages of EFG tensors of all sites visited by the Cd tracer atoms. For Al11La3, the jump frequency at 1073 K was estimated to be 1.9 GHz. Such jump frequencies imply unusually high diffusivities in these phases.
Determination of Grain Boundary Diffusion Coefficients in C-Regime by Hwang-Balluffi Method: Silver Diffusion in Pd
Authors: Balogh Z. , Erdélyi Z. , Beke Dezső L. , Portavoce Alain , Girardeaux Christophe , Bernardini Jean , Rolland Andree
Published: September 2009

Diffusion controlled processes play a crucial role in the degradation of technical materials. At low temperatures the most significant of them is the diffusion along grain boundaries. In thin film geometry one of the best methods for determining the grain boundary (GB) diffusion coefficient of an impurity element is the Hwang-Balluffi method, in which a surface sensitive technique is used to follow the surface accumulation kinetics. Results of grain boundary diffusion measurements, carried out in our laboratory by this method in three different materials systems (Ag/Pd, Ag/Cu and Au/Ni) are reviewed. In case of Ag diffusion along Pd GBs the surface accumulation was followed by AES method. The data points can be well fitted by an Arrhenius function with an activation energy Q=0.99eV
Doping Effect in Nickel Oxide
Authors: Jurasz Zbigniew , Adamaszek Krzysztof , Janik Romuald , Grzesik Zbigniew , Mrowec Stanisław
Published: September 2009

Detailed investigations of nonstoichiometry as well as chemical and self-diffusion in nickel oxide have shown that doubly ionised cation vacancies and electron holes are the predominant defects in this material. The present work is an attempt to demonstrate that aliovalent impurities (Cr, Al, Na and Li) may considerably influence the concentration of these defects and, consequently, the oxidation rate of nickel at high temperatures. It has been shown that small amounts of tri-valent impurities (Cr, Al) bring about an increase of the oxidation rate, while mono-valent ones (Li, Na) decrease the rate of oxidation. These phenomena may satisfactorily be explained in terms of a doping effect. All experiments have been carried out as a function of temperature (1373-1673 K) and oxygen pressure (1-105 Pa) and consequently, it was possible to determine the influence of impurities not only on the oxidation rate but also on the activation energy of reaction and its pressure dependence. The results of these investigations could again be elucidated in terms of doping effect.
Migration of Thermal Vacancies in Quenched Pure AA1050 by Positron Annihilation
Authors: Badawi Emad A. , Abdel-Rahman M.A. , Hassen E.M. , Abdel-Rahman M. , Abdel-Hamed M.O.
Published: September 2009

A description of positron annihilation spectroscopy (PAS) in solids is given in terms of a trapping model. Data are presented for a commercial AA1050 dilute alloy ingot, and fitted to a model allowing presentation in the form of Arrhenius plots. From whence the value of the activation enthalpy, , for thermal vacancies obtained by PAS for AlFeSi is found to be 0.860.18eV.
Determination of Hydrogen Diffusivity in Rail Steels by Sub-Scale Microhardness Profiling Technique
Authors: Moon Abhijeet , Balasubramaniam R.
Published: September 2009

Hydrogen diffusivity was estimated in three different eutectoid rail steels (C-Mn, Cu-Mo and Ni-Cu-Cr) at ambient temperatures using the technique of sub-surface microhardness profiling after cathodic hydrogen charging in 0.5mol/l sulphuric acid at a current density of 0.1A/cm2 for 24 hours. The increase in the concentration of hydrogen at a certain depth below the surface was related to the microhardness increase at this location as compared to the bulk value. The procedure used to obtain the diffusion coefficient of hydrogen from the microhardness profiles is discussed. The hydrogen diffusivity values in all of the rail steels were found to be similar (of the order of 10-13m2/sec). The estimated hydrogen diffusivity in the rail steel was lower than in pure iron (10-8m2/sec). Possible reasons for the difference are discussed.
Heat Treatment of Bi(Pb)-Sr-Ca-Cu-O Thin Films Prepared by Pulsed Laser Deposition
Authors: Jannah A.N. , Halim S.A. , Huda Abdullah
Published: September 2009

Here, Bi(Pb)-Sr-Ca-Cu-O thin films having superconducting properties have been fabricated using Nd-YAG pulsed laser ablation onto single-crystal MgO(100) substrates. The as-deposited film was found to be in an amorphous state. The crystalline structure appeared after the film was annealed in an oxygen environment. The XRD spectrum revealed epitaxial growth of BSCCO (2212) phase at annealing temperatures of 850°C, 860°C and 870°C. In the amorphous state, the microstructure of the films exhibited spherical clusters of various sizes. Upon annealing, plate-like and needle-like structures were observed. These structures fused into grains with a plate-like shape when the annealing temperature reached 870°C. This could be due to the diffusion and arrangement of the components that make up the 2212 phase at elevated temperature in an oxygen environment. The superconducting transition temperature, Tc, is highest for samples annealed at 870°C. The post-annealing procedures were carried out in the ablation chamber in order to minimize contamination.
Structural and Morphological Studies of Porous ZnO for Dye-Sensitized Solar Cell Applications
Authors: Huda Abdullah , Nugroho P.A.
Published: September 2009

Porous nanoflake ZnO has been successfully synthesized via a pyrolitic process of chemical bath deposition (CBD). The latter produced nanoflakes of Zn5(CO3)2(OH)6 as an intermediate product, which transformed to ZnO at 300°C. The microstructure has been investigated by surface morphology observation using a scanning electron microscope (SEM) and crystal-structure analysis using X-ray diffraction (XRD). A random structure of 40nm-thick flakes, grown perpendicularly on the substrate, has been obtained.
Relationship Study among Nanocrystallite Distribution and Roughness of a Nanostructured Hard Layer
Authors: Aliofkhazraei Mahmood , Rouhaghdam Alireza Sabour
Published: September 2009

Up to the fourth moment distributions of carbide nanocrystallites, produced by duplex treatments of surface nanocrystallization and pulsed plasma electrolytic carburizing on AISI316 stainless steel, were investigated to high precision by means of figure analysis. A skewness and kurtosis study of the Gaussian distribution has been made, and the effect of an applied voltage has been determined. It is found that the use of higher applied voltages is more suitable for achieving lower sizes of carbide nanocrystallites. The surface roughness of treated samples was measured and it has been observed that there is an optimum level of applied voltage for surface roughness increase (difference between two measured data).
Effect of Molarity of Precursor Solution on Nanocrystalline Zinc Oxide Thin Films
Authors: Singh Girjesh , Shrivastava S.B. , Jain Deepti , Pandya Swati , Ganesan V.
Published: September 2009

During the last two decades, the use of transparent conducting films of non-stoichiometric and doped metallic oxides for the conversion of solar energy into electrical energy has assumed great significance. A variety of materials, using various deposition techniques, has been tried for this purpose [1-3]. Among these various materials, zinc oxide (ZnO) is one of the prominent oxide semiconductors suitable for photovoltaic applications because of its high electrical conductivity and optical transmittance in the visible region of the solar spectrum [4]. Furthermore, thin films of ZnO have shown good chemical stability against hydrogen plasma, which is of prime importance in a-Si:H-based solar-cell fabrication. Thus, zinc oxide can serve as a good candidate for replacing SnO2 and indium tin oxide (ITO) films in Si:H-based solar cells. One of the outstanding features of ZnO is its large excitonic binding energy, i.e. 60meV, leading to the existence of excitons at room temperature and even at higher temperatures [5-8]. These unique characteristics have generated a wide range of applications of ZnO. For example, gas sensors [9], surface acoustic devices [10], transparent electrodes and solar cells. Many techniques are used for preparing the transparent conducting ZnO films, such as RF sputtering [11], evaporation [12], chemical vapour deposition [13], ion beam sputtering [14] and spray pyrolysis [15–18]. Among these, the spray pyrolysis technique has attracted considerable attention due to its simplicity and large-scale production combined with low-cost fabrication. By using this technique, one can produce large-area coatings without any need for ultra-high vacuum. Thus, the capital cost and the production cost of high-quality zinc oxide semiconductor thin films are lowest among all other techniques. In the present work, we have synthesized ZnO films by using the spray pyrolysis technique. A number of films have been prepared by changing the molarity of the precursor solution. The prepared films have been characterized with regard to their structural, morphological and electrical properties.
A Biomimetic Approach to the Design of the Composite Bottle Cap and Deformation Analyses
Authors: Gu Li Zhi , Zhang Z.
Published: September 2009

On the combination analog of the mussel ripple and leaf embrace, designed a new composite bottle cap consisting of the outer body, the inner lining washer, and the resin embrace, for multi-function, especially for better seal and ready open. According to the structural feature and the functional requirements of the cap, two fundamental components, the lining washer and the outer body, were abstracted into a plate and a cylinder with thin wall, respectively. Under the pressing force the elastic and plastic deformations of both were studied with Tresca’s yielding rule and the limitation of the plastic deformation was presented when the two components were assembled into a unit. For the production of this kind of bottle cap, the maximum value of the allowance press and the maximum pressing velocity were also provided.
Biomimetic Design of Haute-Temperature Lightweight Ceramics: A Review
Authors: Chan Cynthia M. , Ruys Andrew John
Published: September 2009

Functionally graded materials (FGMs) are composite materials in which the properties are varied continuously from one face to the other via a compositional gradient. Functionally graded structures can be found in nature as evident in the cross-sections of bone, teeth and many plant stems, for example bamboo. Initially conceived for the purpose of thermal barrier coatings on spaceplanes, FGMs are finding more applications in other fields such as in polymers, biomedical and semiconductors. In this review, we take a look at two kinds of ceramics, carbon-carbon and fused silica, their properties and processing methods, as well as the possibility of incorporating them in a functionally graded material for use in high-temperature applications. Both carbon and fused silica have similarly low thermal expansion coefficients which will (1) allow the degree of thermal mismatch between the graded layers to be minimized and; (2) reduce the thermomechanical shock that will occur in the presence of a steep temperature gradient.
Tomography Observations of Osteoblast Seeding on 3-D Collagen Scaffold by Synchrotron Radiation Hard X-Ray
Authors: Liou H. , Lin H. , Chen W. , Liou W. , Hwu Y.
Published: September 2009

In recent years, research into three-dimensional (3-D) scaffolds for tissue engineering has become an important topic. To avoid biological rejection, there are many biocompatible materials being developed for in vitro cultivation of autologous cells for implantation into the human body. The 3-D structures of scaffolds are not easily observed using traditional optical or electron microscopes, which only allow examination of the surfaces of samples or ultra thin films, and often require complicated pre-treating processes. The high-brilliance synchrotron radiation (SR) hard X-ray is an emerging technique to acquire tomography. This study involves the successful reconstruction of 3-D images and the animation of the structure of a collagen scaffold. The images were obtained using synchrotron radiation hard X-ray images, which eliminates the need for embedding and microtoming. SR hard X-ray imaging is a non-destructive technique, which has demonstrated a high spatial resolution and transmission, enabling the morphology of osteoblasts adhered on the inner surfaces of the collagen scaffolds to be captured. It is a convenient facility to obtain 3-D tomography images for biomaterial studies. This is the first study to observe the 3-D structures of collagen scaffolds and aquire detailed images of osteoblast attachment on the scaffold, by utilization of third-generation SR hard X-ray radiography.
Effect of Nano-Al2O3 Addition on the Densification of YSZ Electrolytes
Authors: Hotza Dachamir , Leo Adrian , Sunarso Jaka , Diniz da Costa João C.
Published: September 2009

This work investigates the effect of nanosized Al2O3 addition on the sinterability of YSZ electrolyte. (1−x)YSZ + Al2O3 ceramics with compositions x = 0 to 0.01 were prepared by the conventional mixed oxide route from a commercial powder suspension (particle size <50 nm), and sintered at 1200 to 1500°C for 2 hours in air. Densification, phase evolution, and microstructure were characterized by SEM/EDS and XRD. An improvement in sintered density was observed for the samples with 0.2 to 0.5 mol% Al2O3, though depending on the sintering temperature. Only cubic zirconia was detected as crystalline phase, although XRD features suggested chemical interactions depending upon the amount of Al2O3. The grain size of YSZ was homogeneous and no second phase segregation was detected in the tested range of incorporated nano-Al2O3 and sintering temperatures.
Miscibility Enhancement in All-Polymer Nanocomposites Composed of Weakly-Charged Flexible Chains and Polar Nanoparticles
Authors: Montes Sarah , Grande Hans , Etxeberria Agustín , Pomposo Jose A.
Published: September 2009

We report the phase behavior of nanocomposites composed of weakly-charged flexible polymers and polar nanoparticles by extending a mean-field theory for all-polymer nanocomposites recently introduced (Journal of Nano Research 2 (2008) 105). Translational, nanoparticle-driven, electrostatic and enthalpic interaction effects are taken into account. Weakly-charged polymers are predicted to be miscible with polar nanoparticles about one order of magnitude larger (in radius) than conventional uncharged polymers, even in the presence of moderate unfavorable enthalpic interactions. The detrimental effect of addition of a low molecular weight monovalent 1-1 salt on nanocomposite miscibility is also evaluated.
Exploiting the Sequence of Naturally Occurring Elastin: Construction, Production and Characterization of a Recombinant Thermoplastic Protein-Based Polymer
Authors: Machado Raul , Ribeiro A.J. , Padrão J. , Silva D. , Nobre A. , Teixeira J.A. , Arias F.J. , Cunha António M. , Rodríguez-Cabello José C. , Casal M.
Published: September 2009

Genetic engineering was used to produce an elastin-like polymer (ELP) with precise amino acid composition, sequence and length, resulting in the absolute control of MW and stereochemistry. A synthetic monomer DNA sequence encoding for (VPAVG)20, was used to build a library of concatemer genes with precise control on sequence and size. The higher molecular weight polymer with 220 repeats of VPAVG was biologically produced in Escherichia coli and purified by hot and cold centrifugation cycles, based on the reversible inverse temperature transition property of ELPs. The use of low cost carbon sources like lactose and glycerol for bacteria cells culture media was explored using Central Composite Design approach allowing optimization of fermentation conditions. Due to its self-assembling behaviour near 33 °C stable spherical microparticles with a size ~ 1µm were obtained, redissolving when a strong undercooling is achieved. The polymer produced showed hysteresis behaviour with thermal absorbing/releasing components depending on the salt concentration of the polymer solution.
Effect of Annealing on Dielectric Property in Ni1-xCoxFe2O4 Nanoparticles Synthesized Using Albumen (egg white)
Authors: Marutha Senthil S. , Jayaprakash R. , Murthy Sarabu Ramana , Phani A.R. , Singh V.N. , Govindaraj G.
Published: September 2009

The nano crystalline nickel-cobalt ferrite using albumen (egg white) is synthesized by thermal evaporation method and its dielectric behaviour is analyzed for different annealing temperatures. The dielectric property of the sample is measured using impedance analyzer in the frequency range 1-100 MHz. The variation of dielectric constant and dissipation factor under different frequency for the samples at different annealing temperature are analyzed. A steady dielectric constant is observed for the sample annealed at 500°C. The dielectric constant obtained for this sample is low and it is in the range of 18.9 to 6.9 for different frequencies. This low value of dielectric constant shows the less interfacial polarization due to high resistivity which may be to the presence of a few Fe2+ ions. It is observed that the dispersion in dielectric constant by varying the annealing temperature is producing an intended result. The presence of constituent phases in Ni1-xCoxFe2O4 is confirmed by X-Ray Diffraction. The particle size for Ni1-xCoxFe2O4 obtained from Scherrer equation is found to be is 30nm. The morphology, particle size and percentage composition of elements are measured by employing Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis spectrum (EDX).
Towards Silicon-Nanowire-Structured Materials by the Intimate Mixing of Patterning the Solid State and Chemical Reactions
Authors: Hourlier Djamila , Legrand Bernard , Boyaval Christophe , Perrot Pierre
Published: September 2009

Here we describe a simple and effective approach to make silicon-based-nanowires structured materials which can be utilized in a range of high technology electronic devices. The strategy for achieving this objective is to create platforms by lithographic patterning on which the diffusion length of reactive species is controlled during the subsequent heat treatment leading to the growth of aligned and linear nanowires. With this simple and versatile method, a large quantity of nanowires can be readily arranged into interesting configurations. This method is proving very promising for a variety of applications, all of which require considerable selectivity and reproducibility in terms of size, shape and structure, to ensure reliability during their use.
Relationship Between Stickiness and Surface Roughness Of Composite Materials: Atomic Force Microscopy and Intermolecular Adhesion Force Measurement
Authors: Sherman Suryendra D. , Quist Arjan , Hansma Paul
Published: September 2009

Without understanding the property of stickiness there are limits as to how far we can use it and how sticky we can make an object. Understanding of what affects stickiness is critical. Are surface roughness and stickiness related? What is the difference between the sticky and non-sticky objects at a molecular level? We decided to look at the difference between the sticky and non-sticky objects. We reasoned that if we collect sticky and non-sticky objects and compare them through the naked eye, a high powered microscope, and an atomic force microscope (AFM), then the objects that are stickier will have more surface roughness than the objects that are less sticky. Results from our imaging of and analysis of the force of adhesion (which gives a measure of stickiness) between non-sticky objects and sticky objects through the AFM have shown us a different relationship between the surface roughness and stickiness than we had reasoned – the relationship that we have discovered is that stickiness is inversely related to the surface roughness of the materials. Our findings could be used to design new adhesives with different materials that are stronger, lighter and more cost effective that the adhesives used today.
On the Nanostructure of Cu in TixCu1-x and TiN/Cu Films: A XAFS Study
Authors: Pinakidou Fani , Katsikini M. , Patsalas Panos , Abadias Gregory , Paloura E.C.
Published: September 2009

The effect of chemical composition on the bonding environment of Cu, in a series of Ti1-x Cux and TiN/Cu films, is studied using X-Ray Absorption Spectroscopies (XAFS) at the Cu-K-edge. The EXAFS analysis reveals that in all studied samples Cu is amorphous. However, its bonding environment depends on the chemical composition. More specifically, in the Ti1-xCux films, Cu is coordinated with Ti and Cu and belongs both to intermetallic TiCu and to an amorphous Cu matrix. The coordination number of Cu, i.e., the sum of Ti and Cu first neighbours, increases systematically from 6.3 ± 0.7 to 10.6 ± 0.9 when the Cu content increases from 24.1 to 52.7 at%. On the contrary, in the TiN/Cu films, the type of atoms that consists the 1st nearest neighbour shell of Cu varies as a function of the Cu concentration. More specifically, in the TiN/Cu film with the lowest Cu content (27.3 at%), intermetallic TiCu is detected. At intermediate Cu concentration (37.8 at%), Cu is bonded to both Ti and Cu atoms. Finally, in the TiN/Cu film with the highest Cu content (67.7 at%), Cu is metallic.
Fabrication of Nanowires from Gold Nanoparticles by AC Dielectrophoresis and Ink-Jet Delivery
Authors: Tang Jun , Tsoukalas Dimitris
Published: September 2009

A process for nanowire fabrication from gold nanoparticles is described. In this process, we have combined the ink-jet delivery of a nanoparticle colloid with the dielectrophoresis technique. Ink-jet printing is used for the accurate delivery of gold nanoparticle colloid in an exact position and quantity. The nanoparticles dropped to a two electrode gap are ordered into nanowires by the dielectrophoresis force which is induced by the applied AC voltage. The nanowire structures are characterized by microscopy techniques and I-V measurements.
Biological Properties of Ti-Si-C-O-N Thin Films
Authors: Henriques Mariana , Susano Maria , Carvalho Isabel , Ferreri Isabel , Carvalho Sandra , Oliveira R.
Published: September 2009

The main aim of this work was to study the feasibility of new coatings for medical devices. Ti-Si-C-O-N films were deposited by DC unbalanced reactive magnetron sputtering, using different oxygen and nitrogen partial pressure ratios (pO2/pN2). Surface properties were also analysed. Staphylococcus epidermidis was used to study biofilm formation and cytotoxicity was determined using fibroblasts. Surface morphology changed with the increase of pO2/pN2. Samples of high hydrophobicity displayed opposite behaviour in terms of biofilm formation, presenting the highest and lowest biomass. Moreover, the sample with the highest Ti content was the one, with the lowest biofilm amount, raising the possibility of a correlation between Ti and biofilm formation capability. In fact, this sample also displayed the highest degree of cytotoxicity (near 35%). This work shows the feasibility of the proposed coatings and highlights the importance of joining together both biological properties (biofilm formation and cytotoxicity) with the surface characterization.
Diffusion in Intermetallic Compounds and Fabrication of Hollow Nanoparticles through Kirkendall Effect
Authors: Nakajima Hideo , Nakamura Ryusuke
Published: September 2009

. In intermetallic compounds, random vacancy motion is not possible as it would disrupt the equilibrium ordered arrangement of atoms on lattice sites. In view of this limitation, various atomistic models have been proposed, which allow atom-vacancy exchanges to take place without concomitant long range disordering. For a L12 -type A3B structure, the major element A diffuses faster than the minor element B. The trend is attributed to the different diffusing paths; A atoms can diffuse through site exchanges with a neighbouring vacancy on its own sublattice, while the jump of a B atom to a neighbouring site always creates wrong bonds. For L10-type structures such as γ-TiAl, significant diffusion anisotropy is observed; Ti atoms diffuse on the Ti sublattice, while Al atoms also diffuse on the Ti sublattice. The formation of hollow metal oxide nanoparticles through the oxidation process has been studied by transmission electron microscopy for Cu, Zn, Al, Pb and Ni. The hollow structure is obtained as a result of vacancy aggregation, resulting from the rapid outward diffusion of metal ions through the oxide layer during the oxidation process. This suggests the occurrence of two different diffusion processes in the formation of hollow oxides.
Grain Boundary Induced Lateral Propagation of Intermetallic Phases in Nano-Grained Cu-Sn Thin Film Couples
Authors: Kaganovsky Yuri S. , Paritskaya Lyudmila N. , Bogdanov V.V.
Published: September 2009

The kinetics of lateral Cu6Sn5 and Cu3Sn phase propagation induced by grain boundary (GB) interdiffuson in thin-film diffusion couples Cu-Sn were studied in a temperature range 160-180oC by optical microscopy, AFM, SEM, and energy-dispersive X-ray spectroscopy (EDS). Nano-grained Cu and Sn films were sequentially deposited on glass substrates with 5 – 20 µm overlap. To prevent surface diffusion and thus separate GB-diffusion contribution into kinetics of phase propagation, the surfaces of diffusion couples were covered by a thin (20 – 40 nm) carbon layer. It was found that the rates of lateral Cu6Sn5 and Cu3Sn phase spreading in thin-film couples exceed several times the spreading rates of the same phases over the surface of coarse-grained samples and 50 – 70 times exceed the rates in the bulk of massive samples. Kinetics of lateral phase spreading both in thin-film and in massive diffusion couples obeys parabolic law. Similarly to A and B regimes for GB tracer diffusion, A and B regimes of GB reactive diffusion were found in the spreading Cu3Sn phase. The kinetics of the phase propagation turned out independent of the film thickness (in the range 40 – 200 nm) if the films possessed similar grain size, whereas the kinetics was rather sensitive to the grain size and GB structure. Theoretical analysis of the phase propagation kinetics accelerated by GB diffusion has been done and the phase propagation rates have been calculated. By comparison experimentally measured phase propagation rates with the calculated ones we determined the GB diffusion coefficients of Sn in both growing phases.
AFM Study of Typical Fracture Surfaces in Room-Temperature Fracture of Sapphire
Authors: López-Cepero José M. , Wiederhorn Sheldon M. , de Arellano-López António Ramirez , Martínez-Fernández Julian
Published: September 2009

Rhombohedral r-plane fracture surfaces in sapphire are analyzed by optical microscopy and by atomic force microscopy. Features of special interest include steps, lines and angles on the surface that appear to have crystallographic origins. A classification and description of these features is given over a scale ranging from hundreds of micrometers to tens of nanometers. Preferential directions in the surface are identified and related to the crystalline orientation of the sample; an attempt is made to identify the underlying phenomenology behind the appearance of each kind of feature.
TEM Analysis of Wear of Ti/TiN Multi-Layer Coating in Ball-on-Disc Test
Authors: Major Łukasz , Morgiel Jerzy
Published: September 2009

The wear mechanisms of Ti/TiN eight layered coatings ( =250nm) were investigated with ball-on-disc test. The coatings were obtained by hybrid pulsed laser deposition (PLD) technique. The wear test was done using Al2O3 ball-on-disc test at 1N/2000 cycles. Thin foils for TEM observations were cut from wear track using a Quanta 200 3D FIB (Focus Ion Beam) equipped with an Omniprobe lift-up system. The microstructure investigations were performed with the TECNAI G2 SuperTWIN FEG (200kV) transmission electron microscope. At the start of the wear the load applied to Al2O3 ball resulted in pushing-in of the coating into substrate causing its grooving of the shape corresponding to the ball diameter. The lining of the crater required strong coating deformation, which was plastic within Ti and mostly brittle in TiN layers. The vertical cracks in TiN were indeed stopped at the TiN/Ti interfaces, but reopen in lying below TiN layers. In applied wear conditions the continuity of Ti layers prevails over cracking of the TiN layers and resulted in layer-by-layer wear of investigated multilayer coating.
Ultimate Strengthening, Theoretical and Limit Tool Hardness
Authors: Firstov Sergiy A. , Rogul Tamara G. , Gorban Victor F. , Pechkovsky Engel P.
Published: September 2009

The influence of passing from a microcrystalline to a nanocrystalline structure on the mechanical properties of chromium deposited by magnetron sputtering is studied. The possibility of additional strengthening nanomaterials due to enrichment of grain boundaries by “useful” additives elements is established. A wide spectrum of materials in different structural states was investigated by the method of micromechanical tests. The notions of the “theoretical” hardness (largest hardness for the material) and “limit tool” hardness, connected with tool limitations in indentation, are introduced.
Fractal Analysis and Fractography: What Can we Learn that’s New?
Authors: Mecholsky Jr. J.J.
Published: September 2009

The tenets of fractography are well known. The principles of fractal geometry have been applied to fracture surfaces for several decades. How these two fields can be used in a synergistic manner eludes many. The key element in discovering that a fracture surface is fractal is that the features we observe with the naked or aided eye also occur at the atomic scale! Thus, we should be able to interpret the mirror, mist and hackle boundaries in terms of atomic bond breaking. I will present a consistent hypothesis for relating the bond breaking process at the atomic scale to the features we all observe on the fracture surface of materials. I suggest these can be related through one equation: 2 = E a0 D*, where  is the fracture energy, E is the elastic modulus, a0 is a characteristic dimension related to the structure of the material, and D* is the fractal dimensional increment. In turn, D* = c/r1 for which c is the crack size and r1 is the mirror mist boundary radius. Thus, the energy expended in fracture at the atomic scale is encoded on the fracture surface features we observe. The novel combination of fractography, fracture mechanics and fractal geometry can be combined to create a powerful tool for forensic analysis, research investigations and production analyses.
Mechanical Fatigue and Hydrothermal Stability of Y-TZP Dental Ceramics
Authors: Kosmač Tomaž , Oblak Cedomir
Published: September 2009

This study was designed to evaluate the effects of dental grinding and sandblasting on the ageing and fatigue behavior of pressure less-sintered biomedical grade Y-TZP ceramic. It was found that upon dental grinding and sandblasting, the surface of the material was heavily damaged in part plastically deformed, but the amount of transformed monoclinic zirconia was low. The partitioned tetragonal zirconia grains and pre-existing monoclinic zirconia in the ground and sandblasted surfaces hindered the propagation of the diffusion-controlled transformation during subsequent ageing. Dental grinding at a high rotation speed lowered the mean strength under static loading and the survival rate under cyclic loading. Sandblasting, in contrast, resulted in surface strengthening and substantially higher survival rate under cyclic loading. For all tested groups, about 10-15 % lower survival strength values were obtained when tested in artificial saliva, compared to dry specimens, implying that stress-assisted corrosion plays an important role in the fatigue behavior of dental zirconia.
Fractography and Fracture Toughness Measurement
Authors: Morrell Roger
Published: September 2009

Using a variety of advanced ceramic materials, a comparison has been conducted of fracture toughness test methods using the single edge vee-notch beam method and the surface crack in flexure method, the latter restricted to optical fractography. Good agreement has been found between the two methods on materials which were amenable to the SCF method. It has further been shown that the SEVNB method can produce reliable results on materials to which the SCF method is not readily applicable.
Influence of the Sample Size on the Results of B3B-Tests
Authors: Harrer Walter , Danzer Robert , Supancic Peter , Lube Tanja
Published: September 2009

The ball-on-three-balls (B3B)-test is a biaxial strength test for brittle materials. The results of B3B-tests are very stable against small geometrical inaccuracies of the specimens or the test support. In contrast to conventional bending tests there exists only a small influence of friction and edge defects are not relevant. These advantages, compared to beam tests, make the testing of mini-specimens with volumes of a few mm3 feasible. For this investigation silicon nitride specimens of different sizes were tested by use of the B3B-test. The maximum tensile stresses and the effective volumes and effective surfaces of the specimens were determined. The obtained results are compared directly and with the results of conventional 4-point-bending tests and are discussed in the framework of the Weibull-Theory. Additionally fracture surfaces of B3B-specimens and bending specimens were investigated fractographically to identify possible fracture origins.
Fractographic Analysis of Very Small Theta Specimens
Authors: Quinn George D.
Published: September 2009

The theta test specimen is a versatile tool for evaluating the strength of extremely small structures. Round and hexagonal rings are compressed vertically on their ends creating a uniform tension stress in the middle gauge section. The simple compression loading scheme eliminates the need for special grips. A conventional nanoindentation hardness machine with a flat indenter applied load, monitored displacement, and recorded fracture loads. Prototype miniature specimens with web sections as thin as 7.5 m were fabricated by deep reactive ion etching (DRIE) of single crystal silicon wafers. The strength limiting flaws were 200 nm to 500 nm deep surface etch pits.
Fracture of Thin Walled Translucent Polycrystalline Alumina (PCA) Tubes
Authors: Lofaj František , Ivančo Vladimír , Varga Péter Pál
Published: September 2009

Room temperature fracture behavior of short thin walled translucent coarse-grained polycrystalline alumina (PCA) tubes was investigated under compression loading in radial direction using conventional mechanical tests combined with the finite element modelling (FEM). FEM indicated strongly inhomogeneous stress distribution with the maximum tangential tensile stresses in the centre of the inner surface of a tube and opposite to the line of loading. Another zone of tangential tensile stresses form on the outer surface of the tube and oriented perpendicularly to the loading direction. However, these tensile stresses are lower compared to those under contact lines. Radial stresses were negligible compared to tangential stresses which were concluded to control tube fracture. Fracture occurs in two steps: firstly along the loading lines under the lines of contacts and secondly in the direction perpendicular to loading. It results in four regular pieces along the lines with the highest tangential tensile stresses. The results were analysed using Weibull statistics and standard fractography methods. The characteristic strength of the PCA tubes was 186 MPa and the Weibull parameter m‘corr = 16.9 ± 0.5. High m values and the absence of the obvious fracture origins were attributed to homogeneous microstructure and well developed PCA technology.
Crack Growth Resistance of Carbide Reinforced Composite Ceramics Based on Alumina
Authors: Szutkowska Magdalena , Boniecki Marek
Published: September 2009

The relationship of KR versus crack length c (R curve) for Al2O3-30wt.% Ti(C,N).and for comparison alumina ceramics has been examined. The R-curve has been evaluated using pronounced long-crack formed during the three point bending (3PB) of the double edge notched beam. A combination of in situ microscopic crack growth observation and mechanical testing enabled measurement of crack growth resistance curves. The special device consisting of light microscope coupled with CCD camera, was fitted to Zwick 1446 testing machine. These observations reveal the existence of flat R-curve for Al2O3-30wt.% Ti(CN) and increasing R-curve for pure alumina. A study of slow-crack-growth (SCG) in tested materials was carried. The load-relaxation technique was used for observation at slow-crack-growth. The crack length was evaluated by linear-elastic analysis from the compliance of single-edge-notched specimen in three-point bending test. Parameters of stable crack growth n and logA, work-of fracture (WOF), stress intensity factor at the moment of crack initiation KI0 and maximum values of stress intensity factor KImax were determined. Mechanism of grain bridging responsible for occurrence of R-curve was observed by SEM and TEM.