bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative adhesion measures of multilayer films: Part I. Indentation mechanics
Authors: Kriese Michael D. , Gerberich William W. , Moody Neville R.
Published: March 2008

The mechanics for calculating the quantitative driving force of indentation-induced delamination of thin-film multilayers is presented. The solution is based on the mechanics developed by Marshall and Evans [D.B. Marshall and A.G. Evans, J. Appl. Phys. 56, 2632 (1984).] and extended to the general case of a multilayer by use of standard bending and thin-plate analyses. Presented and discussed are the specific solutions for the bilayer case that show that in the limit of zero thickness of either layer, the solution converges to the single-layer case. In the range of finite thickness, the presence of the superlayer increases the driving force relative to that possible for the original film alone and can be optimized to the experimental situation by proper choice of thickness, elastic constants, and residual stress. The companion paper “Quantitative adhesion measures of multilayer films: Part II. Indentation of W/Cu, W/W, Cr/W” discusses experimental results with copper, tungsten, and chromium thin films.
Phase evolution in Ni–Nb multilayers upon solid-state reaction
Authors: Yang G. W. , Lin C. , Liu B. X.
Published: March 2008

Solid-state amorphization was achieved in the Ni48Nb52 multilayers upon thermal annealing by gradually raising the temperature from 250 to 400 °C and staying at 400 °C for 2 h. More interestingly, before complete amorphization, a sequential disordering of first Ni and then Nb crystalline lattices was observed for the first time, and it was essentially the physical origin of an asymmetric growth of the amorphous interlayer during solid-state reaction reported previously in some binary metal systems. In another two multilayered samples with overall compositions of Ni64Nb36 and Ni70Nb30, thermal annealing under similar conditions resulted in the formation of two metastable crystalline phases with face-centered-cubic and hexagonal-close-packed structures, respectively, although an amorphous phase also appeared and coexisted with one of the metastable crystalline phases in the intermediate states. In the ion mixing experiment, such sequential disordering, as well as formation of metastable phases, was also observed in the respective Ni–Nb multilayers upon room-temperature 200-keV xenon ion irradiation. Comparatively, however, ion irradiation eventually induced complete amorphization in all the multilayers at the respective doses, indicating that ion-induced disordering frequently predominated in the competition between amorphization and the growth of a metastable crystalline phase. A Gibbs free energy diagram, including the free energy curves of the newly formed metastable crystalline phases, of the Ni–Nb system was calculated based on Miedema's model. The constructed free energy diagram can give reasonable explanations of the sequential disordering and the thermodynamic possibility of the formation of either an amorphous or a metastable crystalline phase, of which the free energy difference was quite small. It follows naturally that the phase selection, namely, which phase was more favored to be formed eventually than its competitors, was influenced or even determined by the kinetics involved in the respective processes.
Fabrication and properties of organic and metal nanocylinders in nanoporous membranes
Authors: Piraux L. , Dubois S. , Duvail J. L. , Radulescu A. , Demoustier-Champagne S. , Ferain E. , Legras R.
Published: March 2008

Chemical and electrochemical techniques were used for generating ensembles of randomly distributed organic and metal nanocylinders into the pores of nuclear track-etched polycarbonate membranes. This so-called “template method” makes it possible to synthesize a variety of materials including metals, ferromagnets, superconductors, semimetals, and conducting polymer and structures such as solid wires, tubules, composite nanostructures, and multilayers. Numerous interesting properties have been identified in relation to the nanoscopic dimensions of the materials.
Oxidation kinetics of large nickel particles
Authors: Karmhag Richard , Niklasson Gunnar A. , Nygren Mats
Published: March 2008

Oxidation of polycrystalline nickel particles with an approximate median diameter of 158 μm has been studied by thermogravimetric measurements in the temperature range 773–1473 K. The oxidation was found to be thermally activated with an apparent activation energy of about 1.9 eV at temperatures below 1073 K and 1.2 eV at higher temperatures. Our data showed the qualitative features expected for oxidation of spherical metal particles. The kinetics was compared with a homogenous field coupled-currents theory for oxidation of spherical metal particles. Calculations using a median particle size or a distribution of particle sizes could only give a satisfactory fit to part of the experimental data. Possible explanations for the deviations in terms of space charge, grain boundary diffusion, grain growth, and sintering are discussed in this paper. Scanning electron microscopy studies of the particles after oxidation showed that a large difference exists in the surface structure and the degree of sintering between the particles oxidized at low and high temperatures.
Magnetic properties of uniform γ–Fe2O3 nanoparticles smaller than 5 nm prepared by laser pyrolysis
Authors: Morales M. P. , Veintemillas-Verdaguer S. , Serna C. J.
Published: March 2008

γ–Fe2O3 spherical particles with diameters between 5 and 3.5 nm—very uniform in size—have been prepared by laser pyrolysis of iron pentacarbonyl. The infrared spectra of the samples showed features that indicated different degrees of crystallinity according to the preparation conditions. Low saturation magnetization values (≈10 emu/g) and very high coercivities at low temperature (3000 Oe) have been found for the γ–Fe2O3 nanoparticles with the smaller particle size and the highest structural disorder. To explain the magnetic properties, it was necessary to consider additional anisotropies caused by the increase in surface and structural disorder as the particle size decreased.
Influence of heat treatment on LiNbO3 thin films prepared on Si(111) by the polymeric precursor method
Authors: Bouquet V. , Longo E. , Leite E. R. , Varela J. A.
Published: March 2008

The effects of heat-treatment temperature on LiNbO3 thin films prepared by the polymeric precursor method were investigated. The precursor solution was deposited on Si(111) substrates by dip coating. X-ray diffraction and thermal analyses revealed that the crystallization process occurred at a low temperature (420 °C) and led to films with no preferential orientation. High-temperature treatments promoted formation of the LiNb3O8 phase. Scanning electron microscopy, coupled with energy dispersive spectroscopy analyses, showed that the treatment temperature also affected the film microstructure. The surface texture—homogeneous, smooth, and pore-free at low temperature—turned into an “islandlike” microstructure for high-temperature treatments.
C24Cs samples containing oriented N2 molecules
Authors: Finkelstein Y. , Moreh R. , Nemirovsky D. , Shahal O. , Beguin F. , Duclaux L.
Published: March 2008

The adsorption of N2 molecules inside C24Cs has been studied in detail as a function of temperature and pressure using n-diffraction and nuclear resonance photon scattering (NRPS). Large differences were observed between samples derived from highly oriented pyrolytic graphite and those prepared from graphite powder. The tilt angle of the N2 molecular axis was determined by using NRPS and found to lay nearly parallel to the graphite planes. The amount of adsorbed N2 increased with decreasing temperatures, reaching saturation composition C24Cs(N2)1.5 at approximately 100 K with an initial N2 pressure of 2 bar. At higher pressure, 9 bar, two new phases were formed: a second stage C32Cs(N2)2.1 and a first stage C16Cs(N2)1.8 at T < 170 K and are discussed in detail.
Thin films with nanometer-scale pillar microstructure
Authors: Robbie K. , Shafai C. , Brett M. J.
Published: March 2008

Thin films possessing microstructure composed of isolated vertical pillars were deposited by glancing angle deposition (GLAD) without the need for subsequent etch processing. The GLAD technique uses substrate rotation and oblique angle flux incidence to deposit a porous columnar thin film with engineered microstructures. Thin films with a pillar microstructure were fabricated from a variety of metals, metal oxides and fluorides, and semiconductors. The rate and incident angle of vapor flux, as well as the substrate rotation speed during deposition, were found to critically affect pillar microstructure. Thin films with pillar diameters and densities as low as 30 nm and 3 pillars per μm2, respectively, were deposited. The low stress, high surface area, and porous nature of these films suggests use of pillar microstructure films in optical, chemical, biological, mechanical, magnetic, and electrical applications.
Heteroepitaxial growth of bulk single-crystalPb(Mg1/3Nb2/3)O3–32 mol% PbTiO3 from (111) SrTiO3
Authors: Li Tao , Wu Suxing , Khan Ajmal , Scotch Adam M. , Chan Helen M. , Harmer Martin P.
Published: March 2008

SrTiO3 was investigated as an alternate seed material to grow Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) ferroelectric single crystals by seeded polycrystal conversion. Fully dense polycrystalline samples of PMN–32 mol% PT doped with 3 vol% excess PbO were top-seeded with (111) SrTiO3 substrates. Annealing for 10 h at 1150 °C resulted in growth of PMN–32PT single crystals with sizes on the order of several millimeters. Orientation imaging microscopy confirmed that the grown crystal exhibited the same crystallographic orientation as that of the SrTiO3 seed. Elemental distributions analyzed using energy dispersive spectroscopy indicated that interdiffusi on of the relevant elements was negligible.
The deposition of oriented diamond film by hot-filament chemical vapor deposition with separate reactant gas
Authors: Chen G. C. , Sun C. , Huang R. F. , Wen L. S. , Jiang D. Y. , Yao X. Z.
Published: March 2008

A (110)-oriented diamond film was deposited by hot filament chemical vapor deposition with H2 and CH4 separately introduced into the reactive zone. The film with a degree of orientation I(220)/I(111) of more than 200% and deposition rate of 2–3 μm/h was obtained for a deposition time of 17 h. The long deposition time enlarged the grain size and enhanced the degree of orientation, but too long a deposition time resulted in random growth. The temperature field was measured and also calculated using a simple model. Both results showed that a temperature field existed with varied gradients along the normal of substrate surface. The (110)-oriented diamond film was deposited in the zone with negative temperature gradient. The change in orientation occurring for long deposition times was ascribed to the change of temperature gradient.
Synthesis of nanocrystalline diamond by the direct ion beam deposition method
Authors: Sun X. S. , Wang N. , Zhang W. J. , Woo H. K. , Han X. D. , Bello I. , Lee C. S. , Lee S. T.
Published: March 2008

Nanocrystalline diamond has been synthesized on a mirror-polished Si(001) substrate by means of direct ion beam deposition. Low-energy (80–200 eV) hydrocarbon and hydrogen ions, generated in a Kaufman ion source, were used to bombard the substrates. The bombarded samples were characterized by high-resolution transmission electron microscopy and Raman spectroscopy. Nanocrystalline diamond particles of random orientation were observed in a matrix of amorphous carbon film on the Si(001) substrate. The size of the nanocrystalline diamond particles varied in the range of 50–300 Å. The mechanism of ion-induced formation of nanocrystalline diamond is discussed.
In situ boron doping of chemical-vapor-deposited diamond films
Authors: Jiang X. , Willich P. , Paul M. , Klages C-P.
Published: March 2008

A systematic investigation of the boron doping of microwave-plasma-deposited diamond films was performed. Doping with levels up to 550 ppm was carried out in situ on undoped diamond film substrates in a microwave-plasma-assisted chemical vapor deposition with liquid trimethyl-, triethyl-, and tripropylborate and gaseous trimethylborane as doping sources. The dependence of the boron incorporation probability on the doping sources and on the process parameters was studied with secondary ion mass spectrometry. The doping-induced variations of phase quality and morphologic characteristics of the boron-doped diamond layers were investigated by means of scanning electron microscopy and Ramon spectroscopy. The incorporation of other impurities (i.e., hydrogen, nitrogen, oxygen, and silicon) were also determined by secondary ion mass spectrometry. The relations of the concentration of these impurities to the boron incorporation were also studied.
A transmission electron microscopy investigation of SiC films grown on SiC substrates by solid-source molecular beam epitaxy
Authors: Kaiser U. , Khodos I. , Brown P. D. , Chuvilin A. , Albrecht M. , Humphreys C. J. , Fissel A. , Richter W.
Published: March 2008

The relationship between the defect microstructure of SiC films grown by solid-source molecular-beam epitaxy on 4H and 6H–SiC substrates and their growth conditions, for substrate temperatures ranging between 950 and 1300 °C, has been investigated by a combination of transmission electron microscopy and atomic force microscopy. The results demonstrate that the formation of defective cubic films is generally found to occur at temperatures below 1000 °C. At temperatures above 1000 °C our investigations prove that simultaneous supply of C and Si in the step-flow growth mode on vicinal 4H and 6H substrate surfaces results in defect-free hexagonal SiC layers, and defect-free cubic SiC can be grown by the alternating deposition technique. The controlled overgrowth of hexagonal on top of cubic layers is demonstrated for thin layer thicknesses.
Effect of the deposition temperature on the properties of iridium thin films grown by means of pulsed laser deposition
Authors: Khakani M. A. El , Drogoff B. Le , Chaker M.
Published: March 2008

Pulsed laser deposition (PLD) of Ir thin films has been achieved by ablating an iridium target with a KrF excimer laser. The iridium deposition rate was investigated, over the (0.4–2) × 109 W/cm2 laser intensity range, and found to reach its maximum at (1.6 ± 0.1) × 109 W/cm2. At this laser intensity, the PLD Ir films were deposited at substrate deposition temperatures ranging from 20 to 600 °C. The PLD Ir films exhibited a (111) preferentially oriented polycrystalline structure with their average grain size increasing from about 10 to 30 nm as the deposition temperature was raised from 20 to 600 °C. Their mean surface microroughness (Ra) was found to change from an average value of about 1 nm in the 20–400 °C temperature range to a value of about 4.5 nm at 600 °C. As the deposition temperature is varied from 20 to 600 °C, not only does the stress of PLD Ir films change drastically from highly compressive (−2.5 GPa) to tensile (+0.8 GPa), but their room-temperature resistivity also gradually decreases in the 20–400 °C range and stabilizes for higher temperatures. In the 400–600 °C range, the resistivity of PLD Ir films was as low as 6.0 ± 0.2 μΩ cm, which is very close to the iridium bulk value of 5.1 μΩ cm. Thus, PLD Ir films exhibiting not only the lowest resistivity but also a nearly zero stress level can be grown at a deposition temperature of about 400 °C. The resistivity of the PLD Ir films can be described by a grain boundary scattering model.
Effect of Ti + C addition on quenchability and magnetic properties of Nd9Fe85B6
Authors: Zhao T. M. , Xu X. R. , Hu Z. Q.
Published: March 2008

Ingots of composition Nd9Fe85B6, Nd9Fe85B6 + 1 at.% (Ti + C), Nd9Fe85B6 + 2 at.% (Ti + C), and Nd9Fe85B6 + 5 at.% (Ti + C) were prepared by plasma arc-melting the constituent elements from 99.95 wt% Nd, 99.99 wt% Fe, 99.97 wt% Ti, spectrographic grade C, and ferroalloy Fe–B (19.6 wt% B). Effect of Ti + C addition and its content on quenchability and magnetic properties of Nd9Fe85B6 alloy were investigated by melt-spinning. The results showed that the added Ti and C elements reacted with each other to form TiC compound that was solid solutioned, precipitated, or both in the cast ingots. The Ti + C addition can increase the glass-forming ability (GFA) of an α–Fe/Nd2Fe14B–type nanocomposite permanent material: the more the additive, the stronger the GFA; but only approximately 2 at.% Ti + C addition could enormously increase the magnetic properties.
Grain growth in ultrathin films of CoPt and FePt
Authors: Ristau R. A. , Barmak K. , Coffey K. R. , Howard J. K.
Published: March 2008

The microstructure of sputtered 10-nm thin films of equiatomic binary alloys of CoPt and FePt was characterized using transmission electron microscopy (TEM). Grain growth kinetics was examined using manual and digital analysis of bright-field TEM images and was seen to take two stages during annealing in these films. A rapid growth stage concurrent with the formation of a [111] fiber texture was observed to occur within the first 5–10 min of annealing, followed by a much slower growth stage after the fiber texturing was well advanced. Differences in grain growth rate and ultimate grain size were also observed to depend on heating rate.
Synthesis of PbTiO3/organic hybrid from metalorganic compounds
Authors: Yogo Toshinobu , Ukai Hiroyuki , Sakamoto Wataru , Hirano Shin-ichi
Published: March 2008

A nanocrystalline PbTiO3 particle/organic hybrid was synthesized through hydrolysis and polymerization of metalorganic compounds below 100 °C. The PbTiO3 precursor was synthesized from lead methacrylate and titanium isopropoxide. The formation of a Pb–Ti complex alkoxide was confirmed by H and Pb nuclear magnetic resonance spectroscopy. Hydrolyzed Pb–Ti alkoxide was polymerized, yielding the PbTiO3 particles/oligomer hybrid. The organic matrix included nano-sized crystalline particles, depending on the hydrolysis conditions. The nanocrystalline particles were identified to be lead titanate by electron diffraction and energy-dispersive x-ray analysis. The dielectric constant of the nanometer-sized PbTiO3/oligomer hybrid was 5.2 at 10 kHz.
Novel method for the synthesis of thin film coatings on particulate materials
Authors: Fitz-Gerald J. M. , Singh R. K. , Gao H. , Wright D. , Ollinger M. , Marcinka J. W. , Pennycook S. J.
Published: March 2008

In this paper, we show the feasibility of the pulsed-laser ablation technique to grow 20–30-nm-thick, discrete and continuous coatings on particulate material systems so that the properties of the core particles can be suitably modified. Experiments were conducted with a pulsed excimer laser (λ = 248 nm, pulse duration = 25 ns) to deposit nanoparticle coatings on Al2O3 and SiO2 core particles by irradiation of Ag and Y2O3–Eu3+ sputtering targets. Structural characterization was performed with scanning electron microscopy, wavelength dispersive x-ray mapping, transmission electron microscopy, and scanning transmission electron microscopy with z-contrast.
Mechanical properties of Zr57Nb5Al10Cu15.4Ni12.6 metallic glass matrix particulate composites
Authors: Conner R. D. , Choi-Yim H. , Johnson W. L.
Published: March 2008

To increase the toughness of a metallic glass with the nominal composition Zr57Nb5Al10Cu15.4Ni12.6, it was used as the matrix in particulate composites reinforced with W, WC, Ta, and SiC. The composites were tested in compression and tension experiments. Compressive strain to failure increased by more than 300% compared with the unreinforced Zr57Nb5Al10Cu15.4Ni12.6, and energy to break of the tensile samples increased by more than 50%. The increase in toughness came from the particles restricting shear band propagation, promoting the generation of multiple shear bands and additional fracture surface area. There was direct evidence of viscous flow of the metallic glass matrix within the confines of the shear bands.
Pulsed laser deposition of titanium nitride films on sapphire
Authors: Talyansky V. , Choopun S. , Downes M.J. , Sharma R. P. , Venkatesan T. , Li Y. X. , Salamanca-Riba L. G. , Wood M. C. , Lareau R. T. , Jones K. A.
Published: March 2008

We successfully deposited high-quality TiN films on c-plane sapphire by using the pulsed laser deposition technique. TiN grew on sapphire with two in-plane epitaxial relationships: (111)TiN//(0001)sapphire and [101]TiN//[1100]sapphire or (111)TiN// (0001)sapphire and [101]TiN//[1100]sapphire. The TiN unit cell showed a ±30° in-plane rotation for sapphire. The misfit between the TiN film and the sapphire substrate was calculated by using the near coincidence site lattice approach. The deposited films were analyzed by x-ray diffraction, transmission electron microscopy, atomic force microscopy, Rutherford backscattering or channeling spectrometry, electrical, and spectrophotometric measurements. The dependence of the film's crystalline quality on the deposition temperature has been investigated. The full width half-maximum of the rocking curve of the TiN 111 peak was 0.2–0.3°. The minimum ion channeling was 5%, and the room temperature resistivity was as low as 13 μω cm.
Synthesis and characterization of PbTiO3 powders and heteroepitaxial thin films by hydrothermal synthesis
Authors: Chien A. T. , Sachleben J. , Kim J. H. , Speck J. S. , Lange F. F.
Published: March 2008

PbTiO3 powders and heteroepitaxial thin films were produced by the hydrothermal method at 110–200 °C using different bases (Na–, K–, Rb–, Cs–, TMA–, and TBA–OH). Microstructural characterization showed that the tetragonal perovskite films were epitaxial on the SrTiO3 substrates, with a c-axis out-of-plane orientation. Sequential growth experiments showed that the growth initiates by the formation of 100 nm {100} faceted PbTiO3 islands followed by coalescence. Small cation bases (Na–, K–, Rb–OH) produced 1.5-μm {100} faceted blocky powders, whereas larger cation bases (Cs–, TMA–, and TBA–OH) formed fewer 500-nm interpenetrating platelets. Nuclear magnetic resonance results showed cation incorporation in the perovskite structure with local disorder on the Pb sites increasing cation size.
Electrical characterization of BaTiO3 heteroepitaxial thin films by hydrothermal synthesis
Authors: Chien A. T. , Xu X. , Kim J. H. , Sachleben J. , Speck J. S. , Lange F. F.
Published: March 2008

The electrical properties of hydrothermally grown epitaxial pseudocubic BaTiO3 thin films formed on epitaxial electrode layers of SrRuO3 on SrTiO3 single crystal substrates have been evaluated by variable frequency dielectric testing. The initial as-synthesized BaTiO3 film displayed a dielectric constant of 450 with very high losses (tan δ ˜ ~ 100%) at 10 kHz due to OH− and H2O, incorporated during growth, contributing to migration losses within the film. Improvements were seen with increasing postprocessing heat-treatment time and temperature with improved properties seen after a heat treatment at 300 °C for 24 h (ε ˜ ~ 200, tan δ ˜ ~ 8%). Relationships were established for dielectric constant and loss tangent with structural changes observed by Fourier transform infrared spectroscopy, thermal gravimetric analysis, nuclear magnetic resonance spectroscopy, and x-ray diffraction.
Silicon carbide ceramics prepared by pulse electric current sintering of β–SiC and α–SiC powders with oxide and nonoxide additives
Authors: Zhou You , Hirao Kiyoshi , Toriyama Motohiro , Tanaka Hidehiko
Published: March 2008

Using a pulse electric current sintering (PECS) method, β–SiC and α–SiC powders doped with a few weight percent of Al2O3–Y2O3oxide or Al4C3–B4C–C nonoxide additives were rapidly densified to high densities (95.2–99.7%) within less than 30 min of total processing time. When Al2O3–Y2O3additive was used, both ceramics resulting from β–SiC and α–SiC had fine, equiaxed microstructures. In contrast, when Al4C3–B4C–C additive was used, the ceramic resulting from α–SiC had a coarse, equiaxed microstructure, whereas the ceramic resulting from β–SiC was composed of large elongated grains whose formation was accompanied by the β →?α phase transformation of SiC. Compared with the Al2O3–Y2O3-doped SiC ceramics, the Al4C3–B4C–C-doped SiC ceramics had higher densities, lower fracture toughness, and higher hardness. The fracture mode of the oxide-doped SiC was mainly intergranular, whereas the nonoxide-doped SiC exhibited almost complete intragranular fracture that was attributed to the higher interfacial bonding strength.
Fractional factorial design applied to optimize experimental conditions for preparation of ultrafine lanthanum-doped strontium titanate powders
Authors: Yang Wein-Duo , Hsieh Ching-Shieh
Published: March 2008

A fractional factorial design was implemented to optimize the experimental conditions for the preparation of ultrafine lanthanum-doped strontium titanate from titanyl acylate precursors. The effects of preparation conditions such as the molar ratio of acetic acid to titanium alkoxide, the water to titanium alkoxide ratio, pH value, the reaction temperature, and stirring speed were systematically studied by using Taguchi orthogonal array design. Results indicated that the effects of the reaction temperature and stirring speed on the reaction were the key variables influencing the average particle size of powders obtained. By combining the optimal settings of the two influential processing variables, it was possible to obtain an ultrafine powder with a particle size of about 340 Å. This was put to a test in the laboratory, and a polycrystalline, narrow size distribution ultrafine SrTiO3 powder that had a particle size of about 380 Å and readily sintered at 1150–1250 °C was obtained.
Scratch adhesion testing of nanophase diamond coatings on steel and carbide substrates
Authors: Davanloo F. , Collins C. B. , Koivusaari K. J.
Published: March 2008

Films of nanophase diamond are deposited in vacuum onto almost any substrate by condensing multiply charged carbon ions carrying keV energies. These ions are obtained from the laser ablation of graphite at intensities in excess of 1011 W cm−2. The high energies of condensation produce interfacial layers between the film and substrate materials, resulting in levels of adhesion that can support the protection of substrates subjected to harsh environmental conditions. In this article, we give details of the scratch adhesion testing performed on steel and carbide substrates coated with nanophase diamond. A commercially available scratch tester was used and a data analysis was presented to quantitatively assess and measure the adhesion of films on these important substrates. The characterization studies in this work demonstrated nanophase diamond as a highly adherent coating suitable for industrial applications.
Auto ignition synthesis of nanocrystalline MgAl2O4 and related nanocomposites
Authors: Bhaduri S. , Bhaduri S. B. , Prisbrey K. A.
Published: March 2008

Nanocrystalline powders of various compositions in the Al2O3–MgO binary system were synthesized using a novel “auto ignition” process. The respective nitrates were used as starting materials and urea as fuel. Thermodynamic calculations of the adiabatic temperatures were performed for various compositions from Al2O3-rich to the MgO-rich side of the phase diagram. The combustion temperatures of the different compositions were also determined experimentally. The as-synthesized powders were characterized by x-ray diffraction (XRD) and transmission electron microscopy (TEM). As a result of processing, spinel, alumina, magnesia, and solid solutions/ nanocomposites thereof formed. Grain sizes and the lattice parameter were calculated based on XRD results. Where appropriate, the lattice parameter versus the composition of these solid solutions satisfied Vegard's law. Spinel grains were in the 13–20 nm range, alumina grains were 30–40 nm, and MgO grains were 2–28 nm. The grain sizes calculated from XRD results were in good agreement with the TEM results.
Characteristics of dielectric layers formed by low-temperature vacuum ultraviolet-assisted oxidation of SiGe layers
Authors: Craciun Valentin , Boyd Ian W. , Perriere Jacques , Hutton Bernie , Nicholls Edward J.
Published: March 2008

Thin Si0.8Ge0.2 layers epitaxially grown on (100) Si substrates were oxidized at temperatures from 150 to 450 °C under vacuum ultraviolet (VUV) radiation emitted by an excimer lamp working with Xe (λ = 172 nm). The structure and composition of the grown dielectric layers were investigated by Rutherford backscattering spectrometry, nuclear reactions analysis, ellipsometry, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. These investigations have shown that, during the VUV-assisted oxidation process, Ge atoms were initially rejected from the grown SiO2 layer even at temperatures as low as those employed here. After a certain quantity of Ge accumulated at the interface, nanocrystalline Ge regions were directly excised from the remaining SiGe layer becoming embedded within the advancing SiO2 layer. The layers containing these nanocrystalline Ge particles exhibited the same visible photoluminescence spectra as those recorded from layers already known to contain nanocrystalline Ge or GeO2 particles, porous Ge, or nanocrystalline Ge particles exhibiting a different crystalline structure. This seems to indicate that the shell region of the nanocrystalline particle, and not its crystalline core, is the source of the photoluminescence.
Interfacial microstructure formed by reactive metal penetration of Al into mullite
Authors: Lu P. , Du T. B. , Loehman R. E. , Ewsuk K. G. , Fahrenholtz W. G.
Published: March 2008

Microstructures in the reaction interface between molten Al and dense mullite have been studied by transmission electron microscopy to provide insight into mechanisms for forming ceramic–metal composites by reactive metal penetration. The reactions, which have the overall stoichiometry 3Al6Si2O13 + (8 + x)Al → 13Al2O3 + xAl + 6Si, were carried out at temperatures of 900, 1100, and 1200 °C for 5 and 60 min and 1400 °C for 15 min. Observed phases generally were those given in the above reaction; their proportions and interfacial microstructures, however, were strongly dependent on the reaction temperature. Using previously measured reaction kinetics data, the observed temperature dependence of the interfacial microstructure has been modeled as three sequential steps, each of which is rate limiting in a different temperature range.
Interface structure and formation between gold and trimethylcyclohexane polycarbonate
Authors: Bechtolsheim C. v. , Zaporojtchenko V. , Faupel F.
Published: March 2008

This paper presents the results of a systematic investigation of structure and formation of the interface between gold and trimethylcyclohexane polycarbonate, particularly concerning interface evolvement during gold evaporation and the influence of evaporation rate, substrate temperature, and subsequent annealing. The means of investigation were cross-sectional transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. Extensive metal diffusion into the polymer and cluster formation near the interface were observed at deposition rates of the order of one monolayer per minute and below. The penetration depth is strongly temperature dependent. At high evaporation rates metal aggregation at the surface prevents cluster formation inside the polymer. No diffusion into the polymer was observed from metal films deposited at room temperature after extensive annealing at elevated temperatures.
The mechanical behavior of ceramic–metal laminate under thermal shock
Authors: Sherman Dov , Schlumm Doron
Published: March 2008

A new material system for applications involving thermal shock is proposed. The system consists of thin layers of ceramics and thinner metallic interlayers. In this study, a ceramic/metal laminate was constructed from Coor's ADS96R thin plates alternating with thinner Wesgo Cusil Active Braze Alloy interlayer foils and joined in active brazing. The maximum brazing temperature was 845 °C. Square laminated plates were quenched in room-temperature distilled water, where a very large heat transfer coefficient exists, and therefore, severe conditions of thermal shock occur. The laminated plates, initially at temperatures of 600 and 800 °C, were quenched at their bottom surface only in a specially designed apparatus. The temperatures at the top and the bottom surfaces of the specimens were measured by means of two thermocouples during quenching. The basic features of this architecture are described. The dominant behavior was the absence of interaction between the biaxial cracking mechanisms in a ceramic layer with those in an adjacent ceramic layer, and localization of the damage to those layers that experienced sufficient tensile stresses. The result was a dramatic increase of the residual strength after thermal shock. In addition, R-curve behavior upon mechanical loading caused by plastic deformation of the metallic interlayer was observed.
Effect of TiO2 addition on the crystallization of Li2O–Al2O3–4SiO2 precursor powders by a sol-gel process
Authors: Wen Shaw-Bing , Wu Nan-Chung , Yang Sheng , Wang Moo-Chin
Published: March 2008

The activation energy for crystallization of β-spodumene in TiO2 added Li2O–Al2O3–4SiO2 (LAS) precursor powders by a sol-gel process was studied by using isothermal and nonisothermal methods. Nonisothermal kinetics for the LAS precursor powder system were investigated using differential thermal analysis (DTA) and quantitative x-ray diffraction (XRD) analysis. The rate of crystallization of LAS precursor powders decreased as the TiO2 content increased. For samples with addition of 0, 5.0, and 10.0 wt% TiO2, the activation energies for crystallization by DTA evaluation were 165.06, 194.46, and 205.38 kJ/mol, respectively. According to the quantitative XRD method, the values computed by the Johnson–Mehl–Avrami equation were 162.54, 189.42, and 196.14 kJ/mol, respectively. The values obtained by isothermal and nonisothermal kinetic methods from DTA and XRD analyses were in good agreement. The growth morphology parameters were 0.59, 0.70, and 0.76, respectively, for the LAS precursor powder with TiO2 addition of 0, 5.0, and 10.0 wt%, showing a rodlike growth. In the LAS precursor powder system, TiO2 did not act as the nucleative agent.
Effect of divalent cations on the synthesis of citrate-gel-derived lanthanum hexaluminate powders and films
Authors: Cinibulk Michael K.
Published: March 2008

Low-temperature synthesis of hexaluminate phases for fiber–matrix interphases in ceramic–matrix composites is necessary to minimize processing temperatures to prevent fiber-strength degradation. Citrate-gel-derived lanthanum hexaluminate was synthesized using divalent transition-metal cations to stabilize the magnetoplumbite structure. Pure, undoped LaAl11O18was obtained in 1 h only at temperatures >1500 °C after the formation and subsequent consumption of the intermediate perovskite, LaAlO3, which first appeared at ∼1150 °C. Powders of LaMAl11O19, where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn, were prepared at much lower temperatures. Highly crystalline, phase-pure powders of LaMnAl11O19and LaCuAl11O19were obtained at 1000 °C in 1 h directly from the amorphous powder without the formation of the intermediate perovskite. All other compositions could be obtained at 1100 °C in 1 h except for the nominal LaNiAl11O19, which formed primarily LaAlO3, NiAl2O4, and Al2O3. Powders containing dopants all had similar grain sizes and morphologies at 1200 and 1500 °C; the grain size of powders with dopants was significantly greater than that of pure LaAl11O18powder. The introduction of a second charge-compensating quadrivalent dopant for excess divalent cation did not greatly influence synthesis or grain growth below the eutectic temperature but did seem to enhance the [0001] texture of films on single-crystal yttrium-aluminum garnet substrates compared with singly doped films.
Influence of deposition parameters on mechanical properties of sputter-deposited Cr2O3 thin films
Authors: Hones P. , Lévy F. , Randall N. X.
Published: March 2008

Among the oxides, Cr2O3 exhibits the highest hardness value and a low coefficient of friction. These properties make chromium oxide an excellent coating material for tribological applications. Cr2O3 thin films were deposited by radio-frequency reactive magnetron sputtering at substrate temperature in the range 363–593 K. The hardness and elastic modulus of the films were measured by two complementary nanoindentation techniques to investigate the influences of the substrate temperature and the oxygen content in the sputtering gas. While the continuous stiffness data method provides information throughout the whole film thickness, nanoindentation combined with scanning force microscopy of the residual imprints allows visualization of pileup, cracking, and delamination from the substrate. Hardness values up to 32 GPa were obtained for substrate temperatures exceeding 500 K and oxygen contents between 15% and 25% of the total gas pressure. The films, obtained with these deposition conditions, showed good adhesion to silicon substrates.
The Meyer hardness: A measure for plasticity?
Authors: Sakai M.
Published: March 2008

The physical insight into the Meyer hardness is given on the basis of the experimental results for indentation load P versus indentation depth h relations and of a simple model for elastoplastic contact deformation. The quadratic relationships of P = k1h2 for loading and P = k2(h − hr)2 for unloading with the residual depth of impression hr are essential in the elastoplastic indentation processes and mechanisms. The indentation-induced residual strain energy stored in unloaded impression is properly taken into account. The Meyer hardness is an elastic and plastic parameter that depends not only on the plasticity but also on the elasticity of material indented and significantly depends on the geometry of indenter used. The Meyer hardness is given in terms of the energy consumed to create a residual indentation impression, leading to the concepts of “work of indentation” and “ductility index.”
Phase separation in undercooled molten Pd80Si20: Part I
Authors: Lee K. L. , Kui H. W.
Published: March 2008

Three different kinds of morphology are found in undercooled Pd80Si20, and they dominate at different undercooling regimens ΔT, defined as ΔT = T1 – Tk, where T1 is the liquidus of Pd80Si20 and Tk is the kinetic crystallization temperature. In the small undercooling regimen, i.e., for ΔT ≤ 190 K, the microstructures are typically dendritic precipitation with a eutecticlike background. In the intermediate undercooling regimen, i.e., for 190 ≤ ΔT ≤ 220 K, spherical morphologies, which arise from nucleation and growth, are identified. In addition, Pd particles are found throughout an entire undercooled specimen. In the large undercooling regimen, i.e., for ΔT ≥ 220 K, a connected structure composed of two subnetworks is found. A sharp decrease in the dimension of the microstructures occurs from the intermediate to the large undercooling regimen. Although the crystalline phases in the intermediate and the large undercooling regimens are the same, the crystal growth rate is too slow to bring about the occurrence of grain refinement. Combining the morphologies observed in the three undercooling regimens and their crystallization behaviors, we conclude that phase separation takes place in undercooled molten Pd80Si20.
Crystallization of undercooled liquid spinodals: Part II
Authors: Lee K. L. , Kui H. W.
Published: March 2008

We demonstrated in “Phase separation in undercooled molten Pd80Si20: Part I” that when a molten Pd80Si20 ingot is undercooled into its undercooling regimen with ΔT ≥ 220 K (ΔT = T1 – T, where T1 is the liquidus and T is the temperature of the undercooled melt), liquid-state phase separation by spinodal decomposition occurs. On crystallization, one of the metastable liquid spinodals becomes Pd3Si, whereas the other one turns into Pd9Si2. In both cases, Pd particles precipitate out. Microstructural analysis indicates the Pd3Si subnetwork forms first. It then acts as a seed for the subsequent crystallization of the remaining undercooled melt, which finally forms the Pd9Si2 dendrites. As crystallization proceeds, latent heat and volume contraction bring about morphological changes.
Metastable liquid miscibility gap in Pd–Si and its glass-forming ability: Part III
Authors: Hong S. Y. , Guo W. H. , Kui H. W.
Published: March 2008

The metastable liquid miscibility gap of Pd–Si is determined structurally. The glass-forming ability of Pd–Si is then discussed in the light of the metastable liquid miscibility gap. Analysis indicates that it does not favor the formation of glass.
Thermophysical properties of zirconium at high temperature
Authors: Paradis Paul-François , Rhim Won-Kyu
Published: March 2008

Six thermophysical properties of both solid and liquid zirconium measured using the high-temperature electrostatic levitator at the Jet Propulsion Laboratory are presented. These properties are density, thermal expansion coefficient, constant pressure heat capacity, hemispherical total emissivity, surface tension, and viscosity. For the first time, we report the densities and the thermal expansion coefficients of both the solid as well as liquid Zr over wide ranges of temperatures. Over the 1700–2300 K temperature span, the liquid density can be expressed as ρ1(T) = 6.24 × 103 – 0.29(T – Tm) kg/m3 with Tm = 2128 K, and the corresponding volume expansion coefficient as α1 = 4.6 × 10−5/K. Similarly, over the 1250–2100 K range, the measured density of the solid can be expressed as ρs(T) = 6.34 × 103 – 0.15(T – Tm), giving a volume expansion coefficient αs = 2.35 × 10−5/K. The constant pressure heat capacity of the liquid phase could be estimated as Cpl(T) = 39.72 – 7.42 × 10−3(T – Tm) J/(mol/K) if the hemispherical total emissivity of the liquid phase εT1 remains constant at 0.3 over the 1825–2200 K range. Over the 1400–2100 K temperature span, the hemispherical total emissivity of the solid phase could be rendered as εTs(T) = 0.29 – 9.91 × 103 (T – Tm). The measured surface tension and the viscosity of the molten zirconium over the 1850–2200 K range can be expressed as ς(T) = 1.459 × 103 – 0.244 (T – Tm) mN/m and as η(T) = 4.83 – 5.31 × 10−3(T – Tm) mPa s, respectively.
Characterization of thin films containing zirconium, oxygen, and sulfur by scanning electron and atomic force microscopy
Authors: Fischer A. , Jentoft F. C. , Weinberg G. , Schlögl R. , Niesen T. P. , Bill J. , Aldinger F. , De Guire M. R. , Rühle M.
Published: March 2008

Oxidic zirconium films prepared by chemical deposition from aqueous medium on sulfonic acid terminated self-assembled monolayers attached to an oxidized silicon surface were investigated with scanning electron microscopy and atomic force microscopy. Bulk precipitate forms in the 4 mM Zr(SO4)2 · 4H2O, 0.4 N HCl deposition medium at 343 K after approximately 30 min. Precipitate particles (200 nm and larger) were found embedded in the oxidic zirconium film and adsorbed on top of the film; they could be washed off, but patches of the film were removed. Working with unstable deposition solutions, in which homogeneous nucleation occurs, leads to preparation-inherent flaws in the film.
Diffusion of water in crystalline and glassy oxides: Diffusion–reaction model
Authors: Doremus R. H.
Published: March 2008

Diffusion of water in oxides is modeled as resulting from the solution and diffusion of molecular water in the oxide. This dissolved water can react and exchange with the oxide network to form immobile OH groups and different hydrogen and oxygen isotopes in the oxide. The model agrees with many experiments on water diffusion in oxides. The activation energy for diffusion of water in oxides correlates with the structural openness of the oxide, suggesting that molecular water is the diffusing species.
Fracture modes in brittle coatings with large interlayer modulus mismatch
Authors: Chai Herz , Lawn Brian , Wuttiphan Sataporn
Published: March 2008

Fracture modes in a model glass–polymer coating–substrate system indented with hard spheres are investigated. The large modulus mismatch between the glass and polymer results in distinctive transverse fracture modes within the brittle coating: exaggerated circumferential (C) ring cracks that initiate at the upper coating surface well outside the contact (as opposed to the near-contact Hertzian cone fractures observed in monolithic brittle materials); median–radial (M) cracks that initiate at the lower surface (i.e., at the substrate interface) on median planes containing the contact axis. Bonding between the coating and substrate is sufficiently strong as to preclude delamination in our system. The transparency of the constituent materials usefully enables in situ identification and quantification of the two transverse fracture modes during contact. The morphologies of the cracks and the corresponding critical indentation loads for initiation are measured over a broad range of coating thicknesses (20 mm to 5.6 mm), on coatings with like surface flaw states, here ensured by a prebonding abrasion treatment. There is a well-defined, broad intermediate range where the indented coating responds more like a flexing plate than a Hertzian contact, and where the M and C cracks initiate in close correspondence with a simple critical stress criterion, i.e., when the maximum tensile stresses exceed the bulk strength of the (abraded) glass. In this intermediate range the M cracks generally form first—only when the flaws on the lower surface are removed (by etching) do the C cracks form first. Finite element modeling is used to evaluate the critical stresses at crack initiation and the surface locations of the crack origins. Departures from the critical stress condition occur at the extremes of very thick coatings (monolith limit) and very thin coatings (thin-film limit), where stress gradients over the flaw dimension are large. Implications of the results concerning practical coating systems are considered.
A model for front evolution with a nonlocal growth rate
Authors: Jin Shi , Wang Xuelei , Starr Thomas L.
Published: March 2008

In this paper we provide a new mathematical model for front propagation with a nonlocal growth law in any space dimension. Such a problem arises in composite fabrication using the vapor infiltration process and in other physical problems involving transport and reaction. Our model, based on the level set equation coupled with a boundary value problem of the Laplace equation, is an Eulerian formulation, which allows robust treatment for topological changes such as merging and formation of pores without artificially tracking them. When applied to the fabrication of continuous filament ceramic matrix composites using chemical vapor infiltration, this model accurately predicts not only residual porosity but also the precise locations and shapes of all pores.
BaRuO3 thin film electrode for ferroelectric lead zirconate titanate capacitors
Authors: Koo Sang-Mo , Zheng Li-Rong , Rao K. V.
Published: March 2008

The characteristics of a ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) capacitor on conductive BaRuO3 thin films deposited by pulsed laser deposition (PLD) were investigated. The BaRuO3 layer grown epitaxially on LaAlO3(100) substrates at a substrate temperature of 700 °C was found to have a resistivity around 145 μΩ cm at 300 K. The subsequently deposited PZT film showed a c-axis orientation perpendicular to the substrate, and the remnant polarization, ΔP (= P* – P^), and coercive field, EC, of the capacitor were 24.7 μC/cm2 and 52 kV/cm, respectively. Fatigue characteristics of the PZT on BaRuO3 electrodes are far better than those obtained with polycrystalline PZT with Pt structures and comparable to those on epitaxial Yba2Cu3O7−x electrodes. With the new metallic electrode, the PZT layer exhibits no serious degradation in fatigue endurance up to 1010 cycles.