The shear-lag type model due to Cox (Br. J. Appl. Phys. 3, 72 (1952) is widely used to calculate the deformation properties of fibrous materials such as short fiber composites and random fiber networks. We compare the shear-lag stress transfer mechanism with numerical simulations at small, linearly elastic strains and conclude that the model does not apply to random fiber networks. Most of the axial stress is transferred directly from fiber to fiber rather than through intermediate shear-loaded segments as assumed in the Cox model. The implications for the elastic modulus and strength of random fiber networks are discussed.

Insulating epitaxially grown SrTiO3 thin films were prepared on (100)MgO substrates by metal-organic chemical vapor deposition (MOCVD). Semiconductive SrTiO3 thin films were obtained by the rapid cooling after reheating in reduction atmosphere. The microstructure, crystal structure, and electrical properties of these films were investigated. The electrical properties varied by the composition of films and heat-treatment conditions, i.e., the heating temperature, the oxygen partial pressure, and the cooling rate after the annealing. Change of the resistivity of the film was attributed to that of the carrier concentration. Mobility of films was unchanged, and the value was almost the same order of that of bulks. The lowest resistivity of 0.1 Ω·cm was obtained when a sample of Ti/Sr = 1.0 was heated at 1200 °C under 10−15 Pa of PO2 and then rapidly cooled. This value is similar to that of bulks (100 –10−1 Ω · cm).

The samples of Upilex R polyimide (PI) were irradiated with 90 keV N+ ions to the fluences from 5 × 1014 to 2 × 1017 cm−2, and sheet resistance (Rs) and thermoelectric power (TEP) were measured in dependence on the ion fluence and the sample temperature. The Rs achieves its minimum for the ion fluence of 1 × 1017 cm−2, and from the measured temperature dependence of Rs it may be concluded that the ion beam modified PI exhibits semiconductor properties with charge transport governed by the variable range hopping mechanism. The measured TEP of the PI samples irradiated to the fluences above 1 × 1016 cm−2 is low (the order of μV/K). Such properties are typical for metals, and the conclusion is that the charge transport in the irradiated PI samples is contributed by the mechanisms which are characteristic for both semiconductors and metals. The role of conjugated double bonds was examined by measuring absorption UV-VIS spectra. The number of the conjugated double bonds correlates with observed Rs, and the width of the forbidden band, determined from UV-VIS spectra, is a decreasing function of the ion fluence.

Ion implantation of polyethylene terephthalate (PET) and polystyrene (PS) with various high energy metallic ions at 70 kV and a dose of 3 × 1016 ions/cm2 has been made. Measurements of the mechanical properties of the polymers before and after implantation have been made with an ultra microindentation system using both pointed and a small (2 μm) radius spherical-tipped indenter. The surface regions were also investigated by atomic force microscopy (AFM) and Rutherford backscattering (RBS). Significant differences have been observed between the Ti–B dual-implanted surfaces and those of the Au and W implanted surfaces. For both the PET and PS, the resistance to indenter penetration at very low loads was much greater for the Ti–B dual-implanted surfaces. The estimated maximum hardness and modulus of the implanted materials were 0.3 and 8 GPa for the PET material and 1.4 and 16 GPa for the PS material. The results obtained with the spherical indenter show a gradual decline in effective modulus of the surface with penetration depth, whereas the hardness or contact pressure goes through a maximum before declining asymptotically to the bulk values. The values of hardness estimated for the spherical-tipped indenter are somewhat more conservative than the optimistic estimates with the Berkovich indenter. The improved increase in hardness for the Ti–B dual-implanted PET material scales with the RBS measured increased depth of implantation.

Ar+1 ion irradiation on a polycarbonate (PC) surface was carried out in an oxygen environment in order to investigate the effects of surface chemical reaction, surface morphology, and surface energy on wettability of PC. Doses of Ar+ ion were changed from 5 × 1014 to 5 × 1016 at 1 keV ion beam energy by a broad ion beam source. Contact angle of PC was not reduced much by Ar+ ion irradiation without flowing oxygen gas, but decreased significantly as Ar+ ion was irradiated with flowing 4 sccm (ml/min) oxygen gas and showed a minimum of 12° to water and 5° to formamide. A newly formed polar group was observed on the modified PC surface by Ar+ ion irradiation with flowing oxygen gas, and it increased the PC surface energy. On the basis of x-ray photoelectron spectroscopy analysis, the formed polar group was identified as a hydrophilic bond (carbonyl group). In atomic force microscopy (AFM) study, the root mean square of surface roughness was changed from 14 Å to 22–27 Å by Ar+ ion irradiation without flowing oxygen gas and 26–30 Å by Ar+ ion irradiation with flowing 4 sccm oxygen gas. It was found that wettability of the modified PC surface was not greatly dependent on the surface morphology, but on an amount of hydrophilic group formed on the surface in the ion beam process.

The crystallization behavior and microstructure of lithium-calcium aluminogermanate (LCAG) glasses have been studied by using differential thermal analysis (DTA), x-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED). Uniform crystallization of the LCAG glass was found to result from two stages of the heating process. The kinetics of crystallization of the LCAG glasses was studied by DTA using the nonisothermal method. The activation energy for 3CaO · Al2O3 · 3GeO2 crystal growth was 693 kJ/mol. The precipitated crystals determined by XRD analysis were mainly 3CaO · Al2O3 · 3GeO2, and minor phases of 2CaO · Al2O3 · GeO2 and Li2O · Al2O3 · 2GeO2. Morphology and microstructure of the glasses after heat treatment determined by SEM and STEM techniques are presented. Crystallization starts at the surface of the glass sample and then proceeds toward the interior of glass matrix. The morphology of 2CaO · Al2O3 · GeO2 is that of a subangular bell-shaped single crystal growing in a preferred orientation through the segregated phase matrix of fine dispersion of 3CaO · Al2O3 · 3GeO2 crystals. The Li2O · Al2O3 · 2GeO2 phase grows anisotropically in the fine fibrillar morphology and parallel to the [331].

A combination of experiments and detailed kinetic modeling was used to investigate diamond deposition chemistry in low pressure combustion synthesis. Microprobe sampling was employed to provide in situ, quantitative measurements of the stable gas-phase species impinging the growth surface. The reactant gas ratio was found to be the most critical experimental variable. A detailed kinetic model was developed for the stagnation flow system. Comparison of experimental measurements showed very good agreement with model predictions. The model was then used to predict the concentration of radical species and analyze the sensitivity of predictions to γH, the probability of atomic hydrogen recombination on the surface. It was shown that γH dramatically affects the distribution of radical species near the diamond surface. The analysis also indicates that atomic carbon may be an important gas-phase precursor in this system. Comparison of mole fraction measurements and observations of film morphology were used to draw conclusions on the growth mechanism.

The microstructure and electrical properties were investigated for SrTiO3(STO) thin films deposited on Pt/Ti/SiO2/Si substrates by PEMOCVD. The SrF2 phase existing in the STO films deposited at 450 °C influences the dielectric constant, dissipation factor, and leakage current density of STO films. The dielectric constant and dissipation factor of STO films deposited at 500 °C were 210 and 0.018 at 100 kHz, respectively. STO films were found to have paraelectric properties from the capacitance-voltage characteristics. Leakage current density of STO films at 500 °C was about 1.0 × 10-8 A/cm2 at an electric field of 70 kV/cm. The leakage current behaviors of STO films deposited at 500 and 550 °C were controlled by Schottky emission with applied electric field.

Yttria-stabilized cubic zirconia powders and coatings produced by the sol-gel method have been investigated by Perturbed Angular Correlation Spectroscopy (PAC). Results indicate that the metastable cubic phase is retained during heating and cooling cycles. The hyperfine interaction that describes this cubic phase, once crystallized, exhibits two components in a constant ratio of 4 : 1. The components represent different vacancy configurations. For the fast movement of oxygen vacancies starting at 750 °C, which is reflected by the damping of the hyperfine pattern, an activation energy of 0.96 eV was determined.

In the extended x-ray absorption fine structure (EXAFS) study of the local environment of Bi3+ and Pb2+ ions incorporated in Ba4.5Nd9Ti18O54, actual sites of Bi- and Pb-incorporation are determined. Evidence is given that dopant ions are not distributed randomly on all theoretically possible sites; Bi3+ selectively enters one out of three possible channels, corresponding to the sites x = 0.9484, y = 0.2500, z = 0.2939, and/or x = 0.0455, y = 0.2500, z = 0.6928 previously occupied by Nd3+, while Pb2+ selectively enters site x = 0.4940, y = 0.2500, and z = 0.4993 previously shared by Ba2+ and Nd3+.

X-ray reflectivity and diffraction were applied to characterize the highly (100)-textured thin films of LaNiO3, which were deposited on Si substrate via radio frequency magnetron sputtering at temperatures ranging from 250 to 450 °C. Two interference fringes of different period were observed from the reflectivity curves, and the fitting result indicates that in addition to the normal lanthanum-nickel oxide layer, a transition layer, which has a larger mass density than the previous one, exists in the sputter-deposited films. A comparison of the measured x-ray diffraction intensity with that calculated from layer thickness and mass density obtained from reflectivity data indicates that the transition layer is noncrystalline. The x-ray diffraction result also shows that there is a significant decrease of (100) diffraction intensity relative to that of (200) as increasing the deposition temperature. Using the reflectivity and diffraction data along with results of electron diffraction and film composition analysis from our other studies, such a change of relative intensity between the two diffraction peaks is attributed to the increasing content of two also highly textured La-rich phases, i.e., (110)-textured La4Ni3O10 and (100)-textured La2NiO4, in addition to the LaNiO3.

The fabrication of metallic oxide microtubes is possible directly, without any support structure, by continuous wave infrared laser-assisted oxidation of the metal in air. The particular case presented is the growth of tube-like vanadium pentoxide microcrystals grown in our laboratories.

A combustion synthesis (SHS) process has been developed for the synthesis of Si3N4 powder under low nitrogen pressures. Si and NaN3 powders were used as the reactants, and NH4Cl powder was added as a catalytic agent. These powders were mixed and pressed into a cylindrical compact. The compact was wrapped up with an igniting agent (i.e., Ti + C), and the synthesis reaction was triggered by the combustion of the igniting agent. Addition of NH4Cl was found necessary for the combustion synthesis reaction under low nitrogen pressures (< 1.2 MPa). The product as synthesized is mostly in the form of agglomerated fine particles (0.1–1 μm in diameter) and is composed mainly of α-phase and a minor amount of β-phase. Effects of various experimental parameters (N2 pressure, NaN3, NH4Cl, and Si3N4 contents) on the product conversion and the combustion temperature were investigated. A possible reaction mechanism was proposed that explains the effects of the experimental parameters on the synthesis reaction.

This paper deals with the mechanisms and kinetics of interactions between screen printed and fired PbO layers and ceramic substrates: alumina and beryllia. The interaction with alumina occurs via two main processes: (i) a reaction between PbO and Al2O3 grains, which induces the formation of a crystalline phase, Pb2Al2O5; and (ii) an interdiffusion process involving Pb and the intergranular amorphous phase in the ceramic substrate. This latter process results in a compositional change of the intergranular phase at considerable depths inside the ceramic substrate, as well as in the formation of a high lead glass layer on the substrate surface. Since PbO is not completely reacted, the Pb penetration in the ceramic is diffusion limited (penetration depth , where td is the reaction time) with an activation energy of 1.20 ± 0.05 eV. The ceramic microstructure significantly affects the interaction processes.

Camber (curvature) development during cofiring a two-layered structure of Ag film/low-dielectric-constant, low-temperature cofired ceramic (LTCC) green tape has been investigated. At a given thickness of Ag film, both the camber and camber rate decrease linearly with increasing the square thickness of LTCC. Densification mismatch between Ag and LTCC is attributed to be the root cause for the camber generation during cofiring. Mathematical analysis is made to theoretically describe the camber development, and the results show a fairly good agreement with experimental observations.

Strong adhesion between a deposited copper film and an alumina substrate takes place when the substrate is laser-irradiated prior to deposition. A post-deposition annealing is required to achieve the strong bonding. In this work, the interfacial region between the copper film and the alumina substrate was analyzed using Auger Electron Spectroscopy (AES). It was found that a transitional region is always present in couples that have a high adhesion strength, while little or no transitional region was found in weakly bonded couples. The transitional region depends on the laser irradiation atmosphere. In the case of laser irradiation in air, oxygen excess was found on the surface of the alumina substrate, and in the copper/alumina couple the transitional region consists of a copper oxide and a Cu–Al double oxide. When the laser irradiation was performed in a reducing atmosphere (Ar–4% H2), substoichiometric alumina and metallic aluminum were found on the surface of the substrate and also a reaction between copper and the substoichiometric aluminum oxide was detected in the subsurface. Although the substoichiometric alumina is formed on the surface irradiated in Ar–4% H2, a stable Al2O3 thin layer is formed on the outmost surface because the irradiated substrate is exposed to the atmosphere before deposition. This reoxidized layer remains whole at the interface of the couple upon low temperature (at least up to 300 °C) annealing, while it is ruptured upon higher temperature annealing (500 °C in this work). In the latter case, the copper film can contact and react with the substoichiometric alumina formed in the subsurface of the substrate irradiated in the Ar–4% H2 atmosphere. It is concluded that the Cu–Al–O interfacial compound formed in the transitional region causes the strong adhesion between the copper film and the alumina substrate.

An infrared study is made of the chemical changes of synthetic schwertmannite, which normally is a coal oxidation by-product formed by thiobacillus ferrooxidan bacteria. Schwertmannite, a class of minerals, is a metastable compound that transforms to jarosite, hematite, and/or basic iron sulfate at relatively low temperatures, and is analogous in structure to basic iron sulfate, but with a –Fe–O– cage. A proposed formula for schwertmannite is Fe4O4(OH)2·AN(2/e) * nH2O, where AN is the anion and e is its charge, where sulfate can be replaced with other anions, a possible catalyst. The facile conversion of schwertmannite to a black or yellow material might make a useful raw material for the pigment industry.

Lead lanthanum titanate [(Pb, La)TiO3] sol-gel films have been prepared to investigate the effect of heat treatment on the fabrication of uniform and crack-free thick films by applying different heating schedules. The surface morphology as well as the optical properties such as refractive index, optical transmission, and optical propagation loss of the films was examined, depending on the film thickness. Because the slower and longer heating is enough to remove the organic and nitrate residues and diminish the thermal shock while heating the films, slower and longer heating can produce the uniform and crack-free thick films having higher refractive index as well as lower optical propagation loss. Also, the drying and heating of the films on a hot plate in every coating resulted in the fabrication of thick films having above 8000 Å without any defects and microcracks. This film presented the highest refractive index as well as the lowest optical propagation loss which grows exponentially with increasing the film thickness due to the scattering of defects in the film.

Modified lead titanate of 0.9PbTiO3 −0.1Pb(Mg0.5 W0.5)O3 thin films have been deposited onto Pt-coated Si substrates by pulsed laser deposition. Films were crystallized in situ during deposition or by post-depositional heat treatment (post-annealing). Compositional and structural characterization showed that the phase formation and microstructure of the films were highly sensitive to deposition conditions. Perovskite single phase films were formed in situ at 650 °C, PO2 = 40 Pa as well as by post-annealing amorphous films at 650 °C. In the post-annealing process, the amorphous as-deposited phase was crystallized to perovskite and/or pyrochlore, and the ratio of perovskite to pyrochlore was found to be influenced by the depositional PO2. Depending on the deposition temperature, the grain structures of the crystallized films were columnar or equiaxed. A relatively homogeneous surface morphology was obtained by deposition at a lower pressure (PO2 = 13 Pa). The in situ crystallized films showed variable crystallographic orientation. The more (111) oriented films had the lowest remanent polarizations and the highest coercive fields. A method for preparing randomly oriented films, via a two-step deposition process with intermediate annealing, is believed to give the most consistent results and the best ferroelectric properties at the present level of development.

Two refractory phosphors, BaMg2Al16O27: Eu2+ (BAM) and MgAl11O17.5: Ce3+, Tb3+ (MAO), have been synthesized both by the conventional solid-state processing route (using oxides as the starting materials) and by reacting precursors made by the sol-gel process using organic precursors. The phases formed were reacted at 1000 °C in (a) steam and (b) steam + AlF3. The phosphors were well crystallized with particle sizes in the range of 1–10 μm. The emission spectra showed the characteristic broad band blue emission of Eu2+ for BAM and a narrow band green luminescence of Tb3+ for MAO. The melting points of BAM and MAO were measured to be 1920 ± 20 °C and 1950 ± 20 °C, respectively, using an Ir-strip furnace and optical pyrometer. BAM and MAO phosphor materials are congruently and incongruently melting, respectively. Excellent crystallization via the sol-gel route was found even at 1220 °C. Enhancement of the luminescent output by the steam treatment by some 25% was determined.