bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray reflectivity study of solution-deposited ZrO2thin films on self-assembled monolayers: Growth, interface properties, and thermal densification
Authors: Ritley K. A. , Just K-P. , Schreiber F. , Dosch H. , Niesen T. P. , Aldinger F.
Published: March 2008

Thin films of ZrO2were deposited from aqueous solution on Si(100) substrates precovered by functionalized alkyltrichlorosilane self-assembled monolayers (SAMs). The interface structure, thermal stability, and densification of these films in the temperature range from room temperature to 750 °C in vacuum were measured usingin situx-ray reflectivity. The growth rate is a nonlinear function of time in solution, with a pronounced nonuniformity during the first 30 min. The as-deposited films exhibit about 3-nm roughness and a density below that of bulk ZrO2. Measurements in vacuum reveal decreasing film thickness, increasing film density, and decreasing roughness upon annealing up to 750 °C. The densification saturates at the highest measured temperatures, presumably following evaporation of residual contaminants from the aqueous synthesis procedure. Above 200 °C the SAM/ZrO2interface began to deteriorate, possibly due to interdiffusion. The ZrO2film structure obtained at the highest annealing temperatures persisted upon cooling to room temperature, and there was no visible evidence of stress-induced microstructural changes, such as peeling or cracking.
Plasticity contributions to interface adhesion in thin-film interconnect structures
Authors: Lane Michael , Dauskardt Reinhold H. , Vainchtein Anna , Gao Huajian
Published: March 2008

The effects of plasticity in thin copper layers on the interface fracture resistance in thin-film interconnect structures were explored using experiments and multiscale simulations. Particular attention was given to the relationship between the intrinsic work of adhesion, Go, and the measured macroscopic fracture energy, Gc. Specifically, the TaN/SiO2 interface fracture energy was measured in thin-film Cu/TaN/SiO2 structures in which the Cu layer was varied over a wide range of thickness. A continuum/FEM model with cohesive surface elements was employed to calculate the macroscopic fracture energy of the layered structure. Published yield properties together with a plastic flow model for the metal layers were used to predict the plasticity contribution to interface fracture resistance where the film thickness (0.25–2.5 μm) dominated deformation behavior. For thicker metal layers, a transition region was identified in which the plastic deformation and associated plastic energy contributions to Gc were no longer dominated by the film thickness. The effects of other salient interface parameters including peak cohesive stress and Go are explored.
Molecular mechanics of binding in carbon-nanotube–polymer composites
Authors: Lordi Vincenzo , Yao Nan
Published: March 2008

Nanoscale composites have been a technological dream for many years. Recently, increased interest has arisen in using carbon nanotubes as a filler for polymer composites, owing to their very small diameters on the order of 1 nm, very high aspect ratios of 1000 or more, and exceptional strength with Young's modulus of approximately 1 TPa. A key issue for realizing these composites is obtaining good interfacial adhesion between the phases. In this work, we used force-field based molecular mechanics calculations to determine binding energies and sliding frictional stresses between pristine carbon nanotubes and a range of polymer substrates, in an effort to understand the factors governing interfacial adhesion. The particular polymers studied were chosen to correspond to reported composites in the literature. We also examined polymer morphologies by performing energy-minimizations in a vacuum. Hydrogen bond interactions with the ∏-bond network of pristine carbon nanotubes were found to bond most strongly to the surface, in the absence of chemically altered nanotubes. Surprisingly, we found that binding energies and frictional forces play only a minor role in determining the strength of the interface, but that helical polymer conformations are essential.
Microstructural evolution of metallorganic derived Pt-doped TiO2
Authors: Hayakawa Issei , Iwamoto Yuji , Kikuta Ko-ichi , Hirano Shin-ichi
Published: March 2008

A metalorganic precursor containing Ti and Pt was synthesized using Ti alkoxide derivative, amino acid, and platinum salt. The decomposition behavior of the precursor and thin-film formation were examined in terms of microstructure evolution and crystallization. The precursor yielded anatase at 400 °C. Grain growth of platinum particles and TiO2 grains was suppressed even at 800 °C in the films. Suppression of grain growth was attributed to an effect of film thickness.
Hardness obtained from conical indentations with various cone angles
Authors: Cheng Yang-Tse , Li Zhiyong
Published: March 2008

The relationship between hardness and cone angle of conical indenters was studied using finite element analysis for elastic–plastic solids with work-hardening. Comparisons were made between the present simulation results, slip line theory, and experimental results. Tabor's concept of representative strain based on indentation experiments in metals (The Hardness of Metals, Oxford, 1951) was shown to be applicable to a wide range of materials. The relative size of plastic zone with respect to the contact radius was found to influence the variation of hardness with indenter cone angle. The method proposed by Atkins and Tabor [J. Mech. Phys. Solids, 13, 149 (1965)] for constructing stress-strain curves using representative strains was also examined, and the conditions under which the method is valid were obtained.
Am3+ and Eu3+ /alkali cation exchange selectivity on mordenite and zeolite L
Authors: Tsuji Masamichi , Mimura Hitoshi
Published: March 2008

Am3+ and Eu3+ /alkali cation exchange selectivity was studied on mordenite and zeolite L at 25 to 60 °C to examine the effect of their openings of ion-exchange sites. The corrected selectivity coefficient at the infinitesimal exchange increased in the order of Eu3+ < Am3+ on mordenite and Am3+ < Eu3+ on zeolite L. The selectivity reversal did not reflect the effect of the ionic form, but reflected the dimension of the opening of the ion-exchange site and charge of trivalent cations, since the crystal ionic radii of alkali cations were much smaller than the openings of these zeolites (7–8 Å).
Formation of silicate structures in Cu-containing silica xerogels
Authors: Ruiz F. , Martínez J. R. , González-Hernández J.
Published: March 2008

Using infrared absorption and Raman spectroscopy, the structure of SiO2 sol-gel samples containing copper were analyzed as a function of air heat treatments. The weight composition of the samples was 70(SiO2)–30(CuO) and the thermal treatments were carried out in air at various temperatures in the range of 100–600 °C. It was found that the Cu might be incorporated into the SiO2 matrix at least in two ways: forming oxide particles and forming metasilicatelike structures. The copper metasilicate found had the chemical formula, Cu6 [Si6O18] · 6H2O, which is known as dioptase with a thermal stability at temperatures up to 600 °C.
Structures and properties of (001)-oriented Pb(Zr,Ti)O3 films on LaNiO3/Si(001) substrates by pulsed laser deposition
Authors: Kim Sang Sub , Kang Tae Soo , Je Jung Ho
Published: March 2008

In Pb(Zr0.4Ti0.6)O3 (PZT) (110-nm-thick) films grown on (001)-oriented LaNiO3 (LNO) (50-nm-thick)/Si(001) films by pulsed laser deposition, the microstructures and various structural properties of the PZT and the underlying LNO films were comparatively studied mainly using synchrotron x-ray scattering experiments. Basically, the PZT films resembled the LNO films in microstructure, crystal orientation, and mosaic distribution. The PZT films, however, showed an isotropic structural order (in- and out-of-plane coherence lengths: 18 and 14 nm) in contrast to the anisotropic order of the LNO films (in- and out-of-plane coherence lengths: 5 and 30 nm). The PZT/LNO/Si systems displayed a good hysteresis characteristic (remanent polarization, 11.8 μC/cm2; coercive field, 36.1 kV/cm). We confirmed that oriented PZT films with reasonable ferroelectric properties can be successfully prepared on properly textured LNO films at a relatively low processing temperature.
Strongly adhering and thick highly tetrahedral amorphous carbon (ta–C) thin films via surface modification by implantation
Authors: Chhowalla M. , Amaratunga G. A. J.
Published: March 2008

Highly tetrahedral amorphous carbon thin films have exceptional mechanical properties that make them ideal for many challenging wear applications such as protective overcoats for orthopaedic prostheses and aerospace components. However, the use of ta–C in many wear applications is limited due to the poor adhesion and the inability to grow thick films because of the large compressive stress. Here we report on a simple modification of the substrate growth surface by 1-keV ion bombardment using a cathodic vacuum arc (CVA) plasma prior to deposition of ta–C films at 100 eV. The 1-keV C+ ion bombardment created a thin intermixed layer consisting of substrate and carbon atoms. The generation of the intermixed carbide layer improved the adhesion and allowed the growth of thick (several μm) ta–C layers on metallic substrates.
Formation of icosahedral quasicrystal by crystallization of Zr70(Ni, Cu, Pd)30 amorphous alloys
Authors: Zhang T. , Inoue A. , Matsushita M. , Saida J.
Published: March 2008

An icosahedral phase was found to be formed as a primary precipitation phase in the crystallization process of binary Zr70Pd30, ternary Zr70Ni30−xPdx, and Zr70Cu30−xPdx (x = 10 and 20 at.%) and quaternary Zr70Ni10Cu10Pd10 amorphous alloys. The maximum volume fraction of the icosahedral phase was nearly 100% for the 20% Pd alloys and the grain size tended to decrease in the range from 40 to 70 nm with increasing Pd content. No icosahedral phase was formed in the Zr–Ni–Cu alloys without Pd, and hence, the addition of Pd was concluded to be essential for the formation of the icosahedral phase in the Zr-based amorphous alloys. It also was noticed that the icosahedral phase was formed even in the binary Zr70Pd30 amorphous alloy. The icosahedral phase was in a metastable state and changes to equilibrium crystalline phases by annealing in the higher temperature range. The finding of the formation of the icosahedral phase in the binary alloy system allowed us to predict the future appearance of a number of icosahedral base alloys in other alloy systems.
Optical and structural properties of solid oxide photocatalyst Bi2FeNbO7
Authors: Zou Zhigang , Ye Jinhua , Arakawa Hironori
Published: March 2008

Polycrystalline sample of Bi2FeNbO7 was synthesized by the solid-state reaction and characterized by powder x-ray diffraction and Rietveld structure refinement. The optical absorption and structural properties of Bi2FeNbO7 were investigated. It was found that the Bi2FeNbO7 compound has the pyrochlore crystal structure, cubic system with space group Fd3m, and the lattice parameter is a = 10.5233(2) Å. Ultraviolet-visible diffuse reflectance spectroscopy measurement revealed that the band gap of Bi2FeNbO7 is about 2.1(6) eV.
Phase transition, growth, and optical properties of NdxLa1−xSc3(BO3)4 crystals
Authors: Li Yunkui , Aka G. , Kahn-Harari A. , Vivien D.
Published: March 2008

The low-temperature phase, trigonal phase, of space group R32 was discovered in the compound LaSc3(BO3)4 (LSB) doped with arbitrary concentration of Nd3+ ions (NLSB). For LSB, the lattice constants are a = 9.820 ± 0.003 Å, c = 7.975 ± 0.003 Å. The decomposition of NLSB phase was observed in two regions of temperature below and above the congruent melting point by differential thermal analysis and x-ray powder diffraction methods. The single crystals of 2 × 2 × 3mm3 of dominant trigonal phase for x = 0.5 were grown by the flux method (LiBO2). Second harmonic generation effect was observed in NLSB for x = 0 to 1. The concentration dependence of fluorescence lifetime was measured and derived from Dexter's theory of resonant energy transfer.
Thermal analysis investigation of hydriding properties of nanocrystalline Mg–Ni- and Mg–Fe-based alloys prepared by high-energy ball milling
Authors: Berlouis L. E. A. , Cabrera E. , Hall-Barientos E. , Hall P. J. , Dodd S. B. , Morris S. , Imam M. A.
Published: March 2008

The hydrogen loading characteristics of nanocrystalline Mg, Mg–Ni (Ni from 0.1 to 10 at.%), and Mg–Fe (Fe from 1 to 10 at.%) alloys in 3 MPa H2 were examined using high pressure differential scanning calorimetry and thermogravimetric analysis. All samples showed rapid uptake of hydrogen. A decrease in the onset temperature for hydrogen absorption was observed with increasing Ni and Fe alloy content, but the thermal signatures obtained suggested that only Mg was involved in the hydriding reaction; i.e., no clear evidence was found for the intermetallic hydrides Mg2NiH4 and Mg2FeH6. Hydrogen loading capacity decreased with temperature cycling, and this was attributed to a sintering process in the alloy, leading to a reduction in the specific surface available for hydrogen absorption.
Enhanced crystallization and phase transformation of amorphous silicon nitride under high pressure
Authors: Li Ya-Li , Liang Yong , Zheng Fen , Ma Xian-Feng , Cui Suo-Jing , Sun Liling
Published: March 2008

The crystallization and phase transformation of amorphous Si3N4 ceramics under high pressure (1.0–5.0 GPa) between 800 and 1700 °C were investigated. A greatly enhanced crystallization and α–β transformation of the amorphous Si3N4 ceramics were evident under the high pressure, as characterized by that, at 5.0 GPa, the amorphous Si3N4 began to crystallize at a temperature as low as 1000 °C (to transform to a modification). The subsequent a–b transformation occurred completed between 1350 and 1420 °C after only 20 min of pressing at 5.0 GPa. In contrast, under 0.1 MPa N2, the identical amorphous materials were stable up to 1400 °C without detectable crystallization, and only a small amount of a phase was detected at 1500 °C. The crystallization temperature and the a–b transformation temperatures are reduced by 200–350 °C compared to that at normal pressure. The enhanced phase transformations of the amorphous Si3N4 were discussed on the basis of thermodynamic and kinetic consideration of the effects of pressure on nucleation and growth.
Atomic structure of YB56 studied by digital high-resolution electron microscopy and electron diffraction
Authors: Oku Takeo , Bovin Jan-Olov , Higashi Iwami , Tanaka Takaho , Ishizawa Yoshio
Published: March 2008

Atomic positions for Y atoms were determined by using high-resolution electron microscopy and electron diffraction. A slow-scan charge-coupled device camera which had high linearity and electron sensitivity was used to record high-resolution images and electron diffraction patterns digitally. Crystallographic image processing was applied for image analysis, which provided more accurate, averaged Y atom positions. In addition, atomic disordering positions in YB56 were detected from the differential images between observed and simulated images based on x-ray data, which were B24 clusters around the Y-holes. The present work indicates that the structure analysis combined with digital high-resolution electron microscopy, electron diffraction, and differential images is useful for the evaluation of atomic positions and disordering in the boron-based crystals.
Spectroscopic study of a cryptomelane-type manganic acid exchanged by divalent transition-metal cations
Authors: Tsuji Masamichi , Tanaka Yasuo
Published: March 2008

A cryptomelane-type manganic acid (CMA) exchanged by divalent transition-metal cations was studied by means of x-ray diffraction, electron microscopic observation, electron spin resonance, infrared spectra, and electron spectroscopy for chemical analysis. Especially the last three techniques were decisive for the chemical speciation of manganese oxide systems. The findings clearly eliminated a redox process as the principal process for cation uptake in the α–MnO2 phase. Transition-metal cations are stoichiometrically exchanged on this material on an equivalent basis similarly with alkali and alkaline-earth metal cations, except Fe2+. The last ion is oxidized to Fe3+ through a redox reaction with Mn3+ in the a–MnO2. The CMA is a mixed-valence compound represented by H2Mn2IIIMn6IVO16 2.3H2O. Two moles of tunnel protons are exchangeable to give 2.70 mequiv/g for the calculated ion-exchange capacity.
Thermally reversible γ-ray-induced redox reaction between substitutional iron and aluminum impurity centers in a silica glass
Authors: Debnath Radhaballabh
Published: March 2008

The magnetic properties of the substitutional iron and aluminum impurity centers in a sintered Vycor silica glass were studied before and after 1.1–1.3 MeV γ irradiation. Observation of two overlapping spin resonances (g ∼ 4.20–4.28) in the spectra of both the irradiated and preirradiated glasses indicated the existence of two types of tetra coordinated substitutional iron centers of the [FeO4−/Na+]0 type. The intensity of these electron-paramagnetic resonance (EPR) signals decreased upon g irradiation of the glass with concomitant generation of aluminum hole center [AlO4]0, which was manifested by the occurrence of a new six-line EPR signal with g 4 2.009, while thermal annealing of these aluminum oxygen hole centers restores the intensity of the iron centers almost to their preirradiation level. This result suggests that if not the whole, a major fraction of the electrons released in the process of g-ray-induced hole trapping at the Al site are captured by the substitutional iron centers. The electron traps, thus formed, are quite stable and can be deactivated by thermal stimulation.
Formation of NdBa2Cu3O7−δ amorphous phase by combining aero-acoustic levitation and splat quenching
Authors: Nagashio K. , Hofmeister W. H. , Gustafson D. E. , Altgilbers A. , Bayuzick R. J. , Kuribayashi K.
Published: March 2008

Small spherical samples (diameter approximately 2 mm) of NdBa2Cu3O7−δ (Nd123) were fully melted in Ar gas flow in an aero-acoustic levitation device and subsequently rapidly cooled by splat quenching. For samples quenched above the liquidus, the microstructual and x-ray-diffraction (XRD) observations suggested the existence of the amorphous phase with small quantities of the BaCuO2 and BaCu2Ox. The high-temperature XRD results indicated that the decomposition of the amorphous phase, probably assisted by atmospheric CO2 and H2O, led to formation of the BaCO3 phase at 400 °C and, subsequently, the Nd123 phase was formed by the solid diffusion above 800 °C. Another set of Nd123 samples was fully melted in O2 gas flow, undercooled while levitated, and then splat quenched at a temperature below the peritectic temperature (TP). These samples possessed a microcrystalline microstructure of the Nd123 phase that was confirmed by XRD. This indicated that the Nd123 phase was solidified directly from the undercooled melt quenched below TP.
Fractal aggregates of lanthanide-doped Y2O3 nanoparticles obtained by propellant synthesis
Authors: Polizzi Stefano , Fagherazzi Giuliano , Battagliarin Marino , Bettinelli Marco , Speghini Adolfo
Published: March 2008

Y2-xLnxO3 (Ln 4 Ce, Pr, Nd, Eu, Gd, Ho, and Er) powders obtained by propellant synthesis have been characterized using small-angle x-ray scattering, wide-angle x-ray scattering, and transmission and scanning electron microscopy. All the samples showed a very porous, open microstructure with fractal scaling properties. The building blocks of the fractal aggregates are nanocrystallites of lanthanide-doped Y2O3, with variations in the cubic lattice constant proportional to the composition of the solid solution and to the lanthanide ionic radius. The particles had a narrow distribution of sizes with an average value in the 20–50 nm range. They are made of a core of 10–20 nm, consisting of almost perfectly ordered crystals and a “fuzzy” layer, characterized by either a growing lattice disorder or by a compositional gradient. From this dimension, up to at least 200 nm, the particle aggregate is a mass fractal with a fractal dimension, DMf, in the 1.6–2.0 range.
Rheological characteristics of slurry controlling the microstructure and the compressive strength behavior of biomimetic hydroxyapatite
Authors: Guicciardi S. , Galassi C. , Landi E. , Tampieri A. , Satou K. , Pezzotti G.
Published: March 2008

The sponge impregnation of water-based suspensions of hydroxyapatite powders synthesized by the coprecipitation method was investigated. The powder characteristics and slurry properties were correlated with the porosity and mechanical properties of the porous bodies obtained. The rheological characterization in the continuous flow condition revealed a strong dependence of the rheological behavior on the solid loadings particularly with high specific surface area powder. The behavior changed from newtonian to plastic, with pronounced hysteresis effects due to time dependency, by increasing the solids loading from 10 to 18 vol%. The morphology and distribution of the macropores could be related to the starting powder crystallinity and morphology as well as to the rheological properties of the suspensions. The compressive strength of the materials was strongly influenced by the porosity, while there was almost no dependence on the crystallinity of the powder. From a statistical viewpoint, the microporosity better explained the behavior of the mechanical strength than the total porosity.
Preparation of calcium strontium hydroxyapatites by a new route involving calcium phosphate cements
Authors: Leroux L. , Lacout J. L.
Published: March 2008

A new route, based on the use of ionic calcium phosphate cements, has been developed to synthesize hydroxyapatite. Cements were prepared from tetracalcium phosphate, α–tricalcium phosphate, phosphoric acid, strontium nitrate, and water. They were then mixed and shaped. Cements with various amounts of strontium and different (Ca + Sr)/P atomic ratios were prepared. All the materials obtained were coherent and solid. When the amount of strontium was low, mixed hydroxyapatite was obtained at low temperatures. Mixed calcium strontium apatite was obtained after heating. This original method can be of interest in various fields such as biomaterials or the storage of radioactive waste.
Adhesion of benzocyclobutene-passivated silicon in epoxy layered structures
Authors: Hohlfelder Robert J. , Maidenberg Daniel A. , Dauskardt Reinhold H. , Wei Yueguang , Hutchinson W.
Published: March 2008

Adhesion and subcritical debonding at interfaces between a silica-filled epoxy underfill and a silicon die passivated by silicon nitride and benzocyclobutene (BCB) layers were investigated. Adhesion was measured in terms of a critical value of the applied strain energy release rate, G (J/m2). Subcritical debond-growth rates in the range of 10−9to 10−3m/s were characterized as a function of applied G. Adhesion and subcritical debonding were affected by changes in interfacial chemistry and environment. The surprisingly large effect of adjacent layer elastic properties on interfacial adhesion was demonstrated with simulations of interfacial fracture using a mechanics of materials approach. Interfacial chemistry was modified by using different adhesion promoters, by varying the BCB cure state, and by using different epoxy underfill resins. The effects of environmental variables were studied with temperature- and humidity-controlled environments in order to determine the separate roles of moisture activity and temperature.
Refractive index profile and attenuation measurement in KTiOPO4 waveguide by megaelectronvolt He ions
Authors: Wang Ke-Ming , Hu Hiu , Lu Fei , Chen Feng , Shi Bo-Rong , Liu Yao-Gang , Shen Ding-Yu , Wang Xie-Mei
Published: March 2008

An optically polished x-cut KTiOPO4 crystal of size 22×6×1.5mm3 was implanted with 2.8-MeV He ions to a dose of 1.5 × 1016 ions/cm2 at room temperature to form a waveguide. The prism coupling method was used to measure the modes and the fiber probe technique was used to measure the attenuation in the KTiOPO4 waveguide. The refractive index profile, nz, in the KTiOPO4 waveguide was given based on the procedure by Chandler and Lama [P.J. Chandler and F.L. Lama, Optica Acta 33, 123 (1986)]. The waveguide attenuation measured was 2.57 dB/cm for m = 1 mode. After annealing at 260 °C for 30 min, there was no obvious change in the KTiOPO4 waveguide attenuation.
Designing composite microstructures with targeted properties
Authors: Hyun S. , Torquato S.
Published: March 2008

We present a numerical method to find specific composite microstructures with targeted effective properties. The effective properties that may be prescribed are quite diverse and include transport, mechanical, and electromagnetic properties, as well as properties associated with coupled phenomena, such as piezoelectric and thermoelectric coefficients. We formulated the target problem as an optimization problem. To illustrate our general target optimization technique, we have successfully found two-phase composite microstructures having specified effective electrical or thermal conductivities at fixed volume fractions. The method can also be used to design microstructures with multifunctional characteristics.
Sintering and microstructure of glass-coated nanocrystalline yttria-stabilized tetragonal zirconia powder: Effect of the glass
Authors: Ramamoorthy R. , Chaim R.
Published: March 2008

Nanocrystalline yttria-stabilized zirconia (nc-Y-TZP) powders coated with 10 vol% sodium strontium silicate glass were prepared by the sol-gel method. The glass is found to uniformly coat the zirconia particles or particle aggregates. The presence of the glass was found to enhance the densification of the powder compacts leading to 97% of the theoretical density compared to 90% in the pure nc-Y-TZP. It also resulted in a fine microstructure, homogeneous particle shape, and narrow size distribution. The polyhedral-shaped faceted grains in the sintered pure Y-TZP were converted to round-shaped grains in the glass containing specimens
Ferroelectric property of epitaxial Bi4Ti3O12 films prepared by metalorganic chemical vapor deposition
Authors: Watanabe Takayuki , Funakubo Hiroshi , Saito Keisuke
Published: March 2008

The orientation dependence of the ferroelectricity of epitaxially grown Bi4Ti3O12 thin films was investigated. The (001)-, (118)-, and (104)-oriented Bi4Ti3O12 films were epitaxially grown on (100)cCaRuO3//(100)SrTiO3, (110)cSrRuO3//(110)SrTiO3, and (111)cSrRuO3//(111)SrTiO3 substrates, respectively, by metalorganic chemical vapor deposition. Ferroelectric property with different magnitude was observed for (001)- and (118)-oriented films but for (104)-oriented film due to its large leakage current. The remanent polarization and the coercive field were 1.5 mC/cm2 and 15 kV/cm, 16.5 νC/cm2 and 132 kV/cm for the (001)- and (118)-oriented thin films, respectively. The spontaneous polarization (PS) was 4.0 νC/cm2 and 27.0 νC/cm2 for (001)- and (118)-oriented films, respectively. This was different from the result of SrBi2Ta2O9 in that the ferroelectricity was not observed for (001)-oriented one, and was in good agreement with the estimation from the crystal structure. The estimated PS values along the c and a axes of Bi4Ti3O12 were 4.0 and 48.4 νC/cm2, respectively, and agreed well with the reported values for the single crystal. Furthermore, both films showed good fatigue endurance after 7.8 × 1010 switching cycles measured with 500 kHz rectangular pulses.
Erbium doping into lithium niobate and sapphire single crystal wafers
Authors: Nekvindova P. , Spirkova-Hradilova J. , Schröfel J. , Perina V.
Published: March 2008

The possibility of localized doping by Er3+diffusion at moderate (less than 500 °C) temperature was for the first time demonstrated for sapphire single crystal wafers. The doping was achieved by immersing the substrate wafers into reaction melt containing small amounts of erbium salt. The crucial point of the presented technology was a crystallographic orientation of the used wafers. The most suitable orientation of the cuts was the “X-cut” with orientation (11–20). The strong anisotropy of the moderate temperature Er3+doping into lithium niobate and sapphire was explained on the basis of the crystal structure of particular cuts.
Site preference of alloying elements in Fe3Al-based alloys
Authors: Ni Xiao Dong , Chen Nan Xian , Shen Jiang , Sun Zu Qing , Yang Wang Yue
Published: March 2008

On the basis of the first principle interatomic potentials, the site preference of various alloying elements in Fe3Al were evaluated for Ti, Si, Ni, Mn, Mo, and Cr, respectively. The calculated results of the substitutional distribution were in good agreement with the experimental results. Moreover, the calculated results showed that H atoms in Fe3Al prefer to occupy the Fe-type octahedral interstice on the surface, which resulted in concentration of H atoms on the surface. Cr addition decreased the absorbability of Fe3Al-based alloys for H atoms and the force to drive H atoms segregating to surface. The concentration of H atoms on the surface can be decreased by Cr addition.
Investigation of some phenomena occurring during continuous ink-jet printing of ceramics
Authors: Tay B. Y. , Edirisinghe M. J.
Published: March 2008

A ceramic ink was prepared, characterised, and subjected to continuous ink-jet printing. The optimum modulation frequency for printing was estimated. The surface free energies of several substrates were determined and different patterns of the ink droplets were printed on these. Phenomena occurring during the process were investigated. The drop-by-drop resolution and ink spreading were found to be dependent on the dispersive/total surface free energy ratio of the substrates. Ink drying was accompanied by powder migration in the droplets deposited on substrates with a surface free energy lower than the surface tension of the ink. Printing of multiple layers was accompanied by the appearance of ridges, splattering, and non-vertical walls. The causes of these phenomena are discussed in this paper.
Valence variations in titanium-based perovskite oxides by high-pressure and high-temperature method
Authors: Li Liping , Li Guangshe , Miao Jipeng , Su Wenhui , Inomata Hiroshi
Published: March 2008

Typical titanium-based perovskite oxides Eu1−xBaxTiO3 (x = 0.6−0.8), Eu1−xKxTiO3 (x = 0.2,0.32), and La0.7 (Na,K)0.3TiO3 were synthesized by high pressure and temperature using RE2O3 (RE = La,Eu), TiO2, alkaline, or alkaline earth carbonates as the starting materials. X-ray diffraction data analysis showed that there was a structural transformation in Eu1−xBaxTiO3 by varying Ba content [i.e., from cubic (x = 0.6,0.7) to tetragonal (x = 0.8)], and that samples Eu1−xKxTiO3 and La0.7(Na,K)0.3TiO3 crystallized in the cubic perovskite structure. 151Eu Mössbauer spectroscopy and electron paramagnetic resonance measurements revealed mixed valence of Eu2+/Eu3+ in samples Eu1−xBaxTiO3 and Eu1−xKxTiO3, while Ti ions were present in pure Ti4+ state. Cubic Eu1−xKxTiO3 was metastable, which decomposed into a mixture of perovskite and pyrochlore phases at high temperatures as accompanied by an oxidation process from Eu2+ to Eu3+. For samples La0.7 (Na,K)0.3TiO3, Ti3+ signals were clearly observed. The reduction mechanisms for Eu ions at A site and Ti ions at B site in the perovskite oxides are discussed in terms of the chemical nature of the framework ions and substitution ions under high pressure and temperature.
Improved tensile creep properties of yttrium- and lanthanum-doped alumina: a solid solution effect
Authors: Cho Junghyun , Wang Chong Min , Chan Helen M. , Rickman J. M. , Harmer Martin P.
Published: March 2008

The tensile creep behavior of yttrium- and lanthanum-doped alumina (at dopant levels below the solubility limit) was examined. Both compositions (100 ppm yttrium, 100 ppm lanthanum) exhibited a uniform microstructure consisting of fine, equiaxed grains. The creep resistance of both doped aluminas was enhanced, compared with undoped alumina, by about two orders of magnitude, which was almost the same degree of improvement as for materials with higher dopant levels (in excess of the solubility limit). In addition, measured creep rupture curves exhibited predominantly steady-state creep behavior. Our results, therefore, verified that the creep improvement in these rare-earth doped aluminas was primarily a solid-solution effect.
Development of a continuous microscratch technique in an atomic force microscope and its application to study scratch resistance of ultrathin hard amorphous carbon coatings
Authors: Sundararajan Sriram , Bhushan Bharat
Published: March 2008

A method to measure friction during scratching at linearly increasing loads in a commercial atomic force/friction force microscope (AFM/FFM) has been developed. The normal load was increased in small increments over the required range for the scratch using a software module while the friction signal was measured via a breakout box and data acquisition computer. Topography images of the scratch were obtained in situ with the AFM in tapping mode with minimal loss of damage event information. This technique was employed to study the scratch resistance of hard amorphous carbon coatings of thicknesses ranging from 20 nm down to 3.5 nm deposited by different commercially available deposition techniques on a silicon substrate.
Phase-transformation kinetics in triphasic cordierite gel
Authors: Petrović R. , Janacković Dj. , Zec S. , Drmanić S. , Kostić-Gvozdenović Lj.
Published: March 2008

A triphasic cordierite-type gel was prepared from silica sol, boehmite sol, and an aqueous solution of Mg(NO3)2 · 6H2O. The silica sol was obtained from water glass by the ion exchange method, while boehmite sol was obtained by peptization of freshly prepared Al(OH)3. Phase transformations occurring in the gel were studied by differential scanning calorimetry, x-ray diffractometry, and Fourier transform infrared spectrometry. Spinel was observed to crystallize from the gel prior to cristobalite; their reaction subsequently yielded α-cordierite. At higher temperatures, α-cordierite transformed into modulated β-cordierite. Kinetic parameters of α-cordierite formation and α-cordierite to modulated β-cordierite transformation were determined by differential scanning calorimetry under nonisothermal conditions. Formation of a-cordierite was found to be a diffusion-controlled process, with an overall activation energy of Ea = 1242 ± 66 kJ/mol. During the α → β-cordierite transformation, a modulated phase was formed by surface transformation of α-cordierite. The overall activation energy for the formation of the modulated structure is Ea = 583±77 kJ/mol.
Thermal stability of nanocrystalline WC–Co powder synthesized by using mechanical milling at low temperature
Authors: He Jianhong , Ajdelsztajn Leoanardo , Lavernia Enrique J.
Published: March 2008

Nanostructured WC–18% Co powder was synthesized by using cryogenic mechanical milling, and the thermal stability of the nanostructured powder was investigated in detail. The results indicated that the as-synthesized WC–18% Co powder had an average WC particle size of 25 nm. Growth of WC particles occurred above 873 K; however, the average WC particle size remained smaller than 100 nm in the powder isothermally heated for 4 h at 1273 K. Thermal exposure in air at T < 623 K did not result in significant oxidation of the cryomilled powder. The thermal exposure did promote the formation of WO2and WO3oxides. The Co6W6C phase was detected by x-ray diffraction in the powder heated in nitrogen at 1273 K, and the phases associated with decarburization of WC, such as W2C, W3C phases, were not observed. With increasing temperature, the dissolution of W and C elements in the Co matrix led to a gradual increase in {111} crystallographic plane spacing, eventually leading to the formation of an amorphous phase.
Transmission electron microscopy study of (103)-oriented epitaxial SrBi2Nb2O9 films grown on (111) SrTiO3 and (111) SrRuO3/(111) SrTiO3
Authors: Zurbuchen M. A. , Lettieri J. , Jia Y. , Schlom D. G. , Streiffer S. K. , Hawley M. E.
Published: March 2008

Portions of the same epitaxial (103)-oriented SrBi2Nb2O9 film grown on (111) SrTiO3 for which we recently reported the highest remanent polarization (Pr) ever achieved in SrBi2Nb2O9 (or SrBi2Ta2O9) films, i.e., Pr = 15.7 μC/cm2, have been characterized microstructurally by plan-view and cross-sectional transmission electron microscopy (TEM) along three orthogonal viewing directions. SrBi2Nb2O9 grows with its c axis tilted 57° from the substrate surface normal in a three-fold twin structure about the substrate [111], with the growth twins' c axes nominally aligned with the three 〈100〉 SrTiO3 directions. (103) SrBi2Nb2O9 films with and without an underlying epitaxial SrRuO3 bottom electrode have been studied. Dark-field TEM imaging over a 12 μm2 area shows no evidence of second phases (crystalline or amorphous). A high density of out-of-phase boundaries exists in the films.
Quantification and effects of molecular oxygen and water in zinc phthalocyanine layers
Authors: Kerp H. R. , Westerduin K. T. , van Veen A. T. , van Faassen E. E.
Published: March 2008

Gas effusion measurements on zinc phthalocyanine (ZnPc) layers showed the presence of a significant amount of oxygen and water inside the material during exposure to ambient conditions. Of both species the bulk concentration lay in the range of 1020 molecules per cm3. Temperature-dependent analysis indicated that at 296 K all O2 molecules, and roughly one half of the H2O molecules, were mobilized and diffused with diffusion coefficients DO2 of 3 ∗ 10−8 cm2/s and DH2O of 1.3 ∗ 10−10 cm2/s. Electrical analysis of ZnPc layers in controlled atmospheres revealed that the electrical properties of the bulk were determined by O2, whereas H2O influences the surface conductivity. A space-charge density of (1.6 ± 0.2) ∗ 1016 O2− ions per cm3 was measured in atmospheric conditions.
Carrier diffusion characterization in epitaxial 4H–SiC
Authors: Grivickas Paulius , Linnros Jan , Grivickas Vytautas
Published: March 2008

Carrier diffusivity has been experimentally determined in low-doped n-type epitaxial 4H–SiC over a wide injection range using a Fourier transient grating technique. The data showed that, with injection, the diffusion coefficient increased from a minority-hole diffusivity Dh = 2.3 cm2/s to an ambipolar diffusivity Da = 4.2 cm2/s at approximately 1016 cm−3 with a substantial decrease occurring at higher injections. The derived Dh value corresponded to a minority-hole drift mobility of μh = 90 cm2/Vs, about 30% lower than available majority-hole mobilities. Also, the temperature dependence of the ambipolar diffusivity in the 296–523 K range has been determined. It followed a power law Da ∼ T−1.3 which notably differed from the expected one using the majority-hole mobility temperature dependence.
Characterization and modeling of specific strain gradient modulus of epoxy
Authors: Lam D. C. C. , Chong A. C. M.
Published: March 2008

Microscale sensing and actuating components are prevalent in microelectromechanical systems. Deformations of microscale components are dependent not only on the strains in the body, but also on the strain gradients. The contribution of strain gradients to plastic hardening is characterized by the specific strain gradient modulus of the material. The specific strain gradient modulus has been predicted to vary with the plastic strain. The moduli of plastically prestrained epoxy specimens were experimentally characterized in this investigation using nanoindentation. Prestraining induced softening and an energy model are developed to separate the effect of prestrain softening from the effect of strain gradient. The results indicated that the contribution of strain gradient to hardening was initially large but diminished with increased plastic deformation. A model was developed for power law material and was shown to compare well with the experimental results.
Formation and characterization of crystalline iron oxide films on self-assembled organic monolayers and their in situ patterning
Authors: Shin Hyunjung , Jeon Jong Up , Pak Y. Eugene , Im Hyejin , Kim Eung Soo
Published: March 2008

Crystalline and pore-free films of α–Fe2O3 were prepared on hydrophilic self-assembled organic monolayers (DTT-SAMs) at 80 °C. Subsequently, Fe3O4 and γ–Fe2O3 films were synthesized via post annealing of as-deposited α–Fe2O3. In situ patterning of crystalline iron oxide thin layers was achieved via microcontact printing (μCP) and selective deposition. μCP was used to pattern two different surface moieties of self-assembled organic monolayers (SAMs) on Au–Cr–Si substrates. An elastomeric stamp was used to transfer either hexadecanethiol (HDT) SAMs, which are to sustain deposition of iron oxide precipitates, or hydrophilic SAMs [e.g., dithiothreitol (DTT)]. Selective deposition was realized through precipitation of iron oxide phases. Iron oxide films were deposited onto hydrophilic SAMs, but not onto HDT surfaces. Line (width of <1 μm) patterns in crystalline α–Fe2O3 thin films were obtained.
Effective symmetry and physical properties of twinned perovskite ferroelectric single crystals
Authors: Erhart Jiří , Cao Wenwu
Published: March 2008

The effective symmetry and material properties of twinned ferroelectric crystals with perovskite structure were analyzed. The twins or twinbands studied here were formed during ferroelectric phase transitions, which resulted in one of the following symmetry changes: m3m → 3m, m3m → 4mm, and m3m → mm2. It was found that the volume ratios of the two domains in a twin structure were not always equal due to the existence of defect pinning to the domain walls. This unequal partition changed the effective symmetry; hence, the effective macroscopic physical properties of the twin system. Using the data of LiNbO3, BaTiO3, and KNbO3, a detailed analysis has been carried out on macroscopic material property changes caused by the deviation from equal domain volume partition for crystals having 3m, 4mm, and mm2 symmetries.
Fabrication and characterization of microscale sandwich beams
Authors: Arias Francisco , Kenis Paul J.A. , Xu Bing , Deng Tao , Schueller Olivier J.A. , Whitesides George M. , Sugimura Yuki , Evans Anthony G.
Published: March 2008

Microscale sandwich beams with cell diameters and wall widths down to 150 and 15 μm, respectively, and having both metallic and polymer/metal cores were produced through fabrication methods that combined photolithography and electrodeposition. Various core structures were used, including some with negative Poisson's ratio. The bending response was investigated and compared with beam-theory predictions. Most of the cores evaluated had sufficient shear stiffness that the bending compliance was relatively high and dominated by the face sheets. Two of the core configurations were “soft” and exhibited behavior governed by core shear. The relative dimensions of the cores evaluated in this study were far from those that minimize the weight, because of fabrication constraints. The development of an ability to make high-aspect ratio cores is an essential next step toward producing structurally efficient, lightweight microscale beams and panels.
Elastic properties of anisotropic monolithic samples of compressed expanded graphite studied with ultrasounds
Authors: Krzesińska M. , Celzard A. , Marêché J.F. , Puricelli S.
Published: March 2008

The elastic properties of cubic samples of compressed expanded graphite determined by means of ultrasonic velocity measurements are presented. These materials are highly porous and exhibit porosity-dependent anisotropic moduli. The results are analyzed according to two approaches. The first involves semi-empirical equations fitted to the experimental data, resulting in information about the shape and the connectivity of pores. It is found that pores are oblate ellipsoids, connected parallel to their direction of flatness. The second approach is based on application of the percolation theory near the rigidity threshold. The value of the critical exponent indicates that compressed expanded graphites behave like elastic networks in which central forces are predominant. Results of this study give evidence that ultrasound is a convenient and accurate method for investigation of the critical behavior of the elastic properties in highly tenuous structures.
Comparison of hydrophilic properties of amorphous TiOx films obtained by radio frequency sputtering and plasma-enhanced chemical vapor deposition
Authors: Nakamura Masatoshi , Aoki Toru , Hatanaka Yoshinori , Korzec Dariusz , Engemann Jurgen
Published: March 2008

The hydrophilic properties of amorphous TiOx films prepared by different methods, e.g., radio frequency (rf) sputtering and plasma-enhanced chemical vapor deposition (PECVD), were studied. It was found that the hydrophilicity strongly depends on the film structure. The best hydrophilicity was realized with the PECVD amorphous film having distorted Ti–O bonds due to a large amount of OH groups. These characteristics of the PECVD amorphous film suggest that such a low-density film including distorted Ti–O bonds could increase the photoenhancement efficiency by ultraviolet radiation. This reason is also supported from the results that a low-density rf sputtered film presented a higher hydrophilicity compared to a high-density radio frequency sputtered film. Furthermore, both electrical and chemical effects of OH groups will also contribute to the good hydrophilicity of the PECVD film.
Thermal conductivity and thermal diffusivity of selected oxide single crystals
Authors: Stanimirovic A. , Balzaretti N. M. , Feldman A. , Graebner J. E.
Published: March 2008

Values for the thermal conductivity κ and the thermal diffusivity D of four oxide single crystals were obtained. Near room temperature, the values for κ (W cm−1 K−1) and D (cm2 s−1) are as follows: LaAlO3, κ = 0.115, D = 0.0446; NdGaO3, κ = 0.068, D = 0.0197 for one structural orientation, and κ = 0.059, D = 0.0195 for an orthogonal orientation; (LaAlO3)0.3–SrAl0.5Ta0.5O3, κ = 0.051, D = 0.0133; and, ScAlMgO4, κ = 0.062, D = 0.0229. The relative standard uncertainties in these values are ±10% (1 σ). These values allowed us to calculate the specific heat of the materials. The thermal conductivity was measured by a dc heated bar method, and the thermal diffusivity was measured by a modification of Ångström's method.
Synthesis and characterization of antimony oxide nanoparticles
Authors: Zhang Zaoli , Guo Lin , Wang Wendong
Published: March 2008

Antimony oxide nanoparticles were synthesized in the presence of the polyvinyl alcohol in water solution through the reaction between SbCl3 and NaOH. The size of the particle ranges from 10 to 80 nm, and the largest one can even reach 200 nm, which may begin to grow in the initial stage of the reflux. Transmission electron microscopy and high-resolution electron microscopy (HREM) were used to characterize the microstructure of these nanoparticles. Using silicon single crystals as internal standards, the polycrystalline diffraction pattern analysis shows only presence of cubic Sb2O3 phase. The bright-field micrograph displays that the particles may have various polyhedral configurations. HREM results show that the particles are crystallographically perfect. Moreover, the formation mechanism of nanoparticles is discussed.