Microstructures of well-aligned multiwall carbon nanotubes grown on patterned nickel nanodots and uniform thin films by plasma-enhanced chemical vapor deposition have been studied by electron microscopy. It was found that growth of carbon nanotubes on patterned nickel nanodots and uniform thin films is different. During growth of carbon nanotubes, a nickel particle sits at the tip of each nanotube, and its [220] is preferentially oriented along the plasma direction, which can be explained by a channeling effect of ions coming into nickel particles in plasma. The alignment of nanotubes is induced by the electrical field direction relative to substrate surface.

The growth of large, melt-textured Nd1+xBa2−xCu3O6+δ (Nd-123) crystals has been achieved by hot seeding and isothermal solidification under a 1% oxygen in nitrogen atmosphere. These crystals, which exhibit a sharp, faceted growth interface, were grown epitaxially from a small Nd-123 single crystal seed placed on the sample surface at elevated temperature. The growth length of the melt-processed crystal was directly proportional to the isothermal holding time (approximately 17 h), as is observed for the growth of YBa2Cu3O7−δ (Y-123). The variation of growth rate with undercooling for this material was linear, however, in contrast to the parabolic dependence observed for Y-123 crystals grown in air. The growth rate of Nd-123 under reduced oxygen was consequently lower than that of Nd-123 and Y-123 grown in air at relatively high values of undercooling. Evaluation of the experimental data against a solidification models suggested that the interface kinetics are responsible, at least in part, for the observed growth features in hot-seeded Nd-123 crystals. This was attributed to the difference in oxygen partial pressure under the respective growth atmospheres, rather than to the species of rare-earth element in the compound.

The effect of mechanical and field activation on the synthesis of dense nanometric MoSi2 was investigated. Powders of Mo and Si, milled separately or comilled in a planetary ball mill, were reacted in a spark plasma synthesis (SPS) apparatus under different electric current conditions. Milled powders reacted faster and required less current than unmilled powders. Mixtures of powders which were milled separately (to nanometric size) reacted in the SPS to produce micrometric α–MoSi2. Similar results were obtained for samples comilled to produce nanometric reactants which did not contain detectable amounts of the product phase. When products form during milling, they contain both the α and β modifications of MoSi2. The product after the SPS reaction was nanometric MoSi2 with a crystallite size of 140 nm.

We describe a method for controlled preparation of sol-gel ceramic multilayer coatings obtained by dip-coating. The proposed fabrication routine guarantees obtaining crack-free multilayer coatings with control of the thickness and porosity of individual layers. The procedure is applied to obtain a 10-layer ZrO2–3 mol% Y2O3 coating deposited on AISI 310 stainless steel. The microstructure of this coating was investigated by using x-ray powder diffractometry and atomic force microscopy, and special consideration was given to the mechanical characterization of this thin film using ultramicrohardness indentation tests. Our results suggest that these zirconia coatings have good properties for use as protection barriers. Implications concerning general tailoring design of sol-gel dip-coatings are also considered.

ZnO:Al (ZAO) films were deposited on fused silica substrates heated to 350 °C by dc magnetron reactive sputtering from a Zn target mixed with 1.5 wt% Al. Films deposited on a substrate heated to a temperature between room temperature and 300 °C were (001)-oriented crystals, but those grown at 350 °C consisted of crystallites with (001) and (101) orientations. The dependence of electrical properties such as resistivity, carrier concentration, and Hall mobility on temperature was measured. The results indicate that the carrier concentration and Hall mobility increase with increasing temperature up to 250 °C, though the Al content remains unchanged in this temperature range. The probable mechanisms are discussed. The minimum resistivity of ZAO films is 4.23 × 10−4 Ω cm, with a carrier concentration of 9.21 × 1020 cm−3 and a Hall mobility of 16.0 cm2 v−1 s−1. The films show a visible transmittance of above 80%.

The combustion of zirconium foils in an oxygen environment was investigated for foils ranging in thickness from about 22 to 124 μm and for oxygen partial pressures ranging from about 0.3 to 0.9 atm. Temperature profile measurements showed indications of an after-burn, which became especially significant in the combustion of thicker foils. The dependence of the combustion wave temperature and velocity on the oxygen partial pressure was determined. For any partial pressure, wave velocity decreased with an increase in foil thickness. Wave propagation in this system is a complex process and is dictated by oxide formation and oxygen dissolution. The results are examined in light of a finite difference model.

This article describes a convenient, noncontacting technique for determining the flexural rigidity and residual stress in thin membranes. The method was based on transient grating photoacoustics, also known as impulsive stimulated thermal scattering. Crossed laser pulses provided a coherent source of wavelength tunable acoustic modes in the membranes. Diffraction of a probe laser revealed the time dependence of these motions. The measured dispersion of the lowest-order Lamb mode at small acoustic wavevectors, coupled with classical plate theory, allowed the flexural rigidity and the residual stress to be determined. The technique, its accuracy, and spatial mapping capabilities were demonstrated through analysis of membranes designed for masks in next-generation lithography systems based on projected beams of electrons.

Nanoindentation is a technique commonly used for measuring thin film mechanical properties such as hardness and stiffness. In this study, we used the finite element method to investigate the effect of substrate and pileup on hardness and stiffness measurements of thin film systems. We define a substrate effect factor and construct a map that may be useful in the interpretation of indentation measurements when it is not possible to make indentations shallow enough to avoid the influence of the substrate on the measurements. A new technique for measuring mechanical properties of thin films by nanoindentation is suggested at the end of this article.

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.

Heating and annealing effects on the optical properties of slightly blue substoichiometric molybdenum trioxide thin films are reported partially. During heating and annealing, different levels of coloration seem to be generated by simultaneous reduction and proton injection into thin films, which cause the formation of hydrogen molybdenum bronzes of different concentrations. The optical band gap, Eo, of MoO3 thin film when annealed in between 313 and 473 K is decreased to 2.82 eV, and this reduction in Eo has been explained with a view to phonon and polaron species. Moreover, temperature-dependent change in the optical band gap has also been interpreted in terms of band gap slope, B, and the real part of the refractive index, n. Urbach slope, σ, also goes down to 0.67 eV−1 due to annealing treatment. Using the oscillator model, a phonon energy, hνo, of about 0.08 eV was found for the reported MoO3 thin film which is very close to the characteristic phonon energy of MoO3. Over and above, the intensity for the blue absorption band, over the photon energy range 0.4–3.0 eV, also reaches a maximum as MoO3 thin film is annealed at 473 K for 1 h and then decreases by 32% after annealing at the same temperature for 2 h. This phenomenon is due to polaronic band intensity which rises and falls during annealing. Half-width of the blue band, as found by fitting polaron model, is changed only by 3% on annealing the MoO3 thin film at 473 K as compared to its value at room temperature.

This paper reports a study of plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) as a suitable technique for depositing dense, crack-free thin layers of yttria-stabilized zirconia onto porous substrates, as a step in the fabrication of anode-supported planar solid oxide fuel cells (SOFC). Our objective is to present an alternative method by which an SOFC assembly may be fabricated at lower temperature than by conventional methods. PE-MOCVD using zirconium tertbutoxide (ZrTB) -and yttrium hexafluoroacetylacetonate dihydrate (Y6FA) is capable of producing the electrolyte in thin dense layers on smooth surfaces, as demonstrated for Si(110) wafers. If a porous substrate is used, the average surface pore size should not exceed 1–2 μm to obtain a dense film. The crystalline phase of the film was related to the Y6FA concentration in the gas phase using x-ray diffraction. Depth profiling, using x-ray photoelectron spectroscopy, showed that Y is present (fairly uniform) at all depths of the film. Growth rates are dependent on the applied power but independent of substrate temperature. Film density, however, shows a significant dependence on substrate temperature.

We have studied the glass transition behavior of vitreous As2Se3 by carrying out temperature-modulated differential scanning calorimetry (TMDSC) and conventional differential scanning calorimetry (DSC) experiments to measure the glass transition temperature Tg. In TMDSC experiments we have examined the reversing heat flow (RHF), that is the complex heat capacity CP in the glass transition region as the glass is cooled from a temperature above the glass transition temperature (from a liquidlike state) and also as the glass is heated starting from room temperature (from a solidlike state). The RHF, or CP versus T, in TMDSC changes sigmoidally through the glass transition region without evincing an enthalpic peak which is one of its distinct advantages for studying the glass transformations. The Tg measurements by TMDSC were unaffected by the amplitude of the temperature modulation. We have determined apparent activation energies by using Tg-shift methods based on the Tg-shift with the frequency (ω) of temperature modulation in the TMDSC mode and Tg-shift with heating and cooling rates, r and q, respectively, in the DSC mode. It is shown that the apparent activation energies ∆h* obtained from ln ω versus 1/Tg and ln q versus 1/Tg plots are not the same, but nonetheless, they are approximately the same as the apparent activation energy ∆hn of the viscosity over the same temperature range where the empirical Vogel expression of Henderson and Ast, η = 12.9 exp[2940/(T - 335)], was used for the viscosity. The latter observation is in agreement with the assertion that the structural relaxation time Ʈ is proportional to the viscosity h. The apparent activation energy ∆hr obtained from the ln r versus 1/Tg plot during heating DSC scans is lower than ∆h* observed during cooling scans. The results are discussed in terms of a phenomenological Narayanaswamy type relaxation time. It was observed that Tg obtained from TMDSC cooling experiments did not depend on the underlying cooling rate for q ≤ 1 °C min-1; and for temperature amplitudes 0.5–5 °C. The transition due to the temperature modulation was well separated from the transition due to the underlying cooling rate. Further, the apparent activation energies obtained from ln ω versus 1/Tg during cooling and heating scans for q and r ≤ 1 °C min−1 are approximately the same as expected from Hutchison's calculations using a single relaxation time model of TMDSC experiments.

Fiber texture in Ti/Al and Nb/Al polycrystalline multilayer thin films, with bilayer thicknesses (Λ) ranging from 20–333 nm and having a fixed stoichiometry of 1/3, has been investigated by using x-ray pole figures and transmission electron microscopy. Two sets of films were deposited; one set contained pure Al and the other Al–1.0 wt% Cu. The results indicated that texture was strengthened by the formation of a coherent superlattice for the Nb/pure-Al film with the smallest bilayer thickness. By contrast, the texture in Ti/pure-Al films with a similar period was not as strong. The texture also decreased with increasing Λ for both the Ti/pure-Al and Nb/pure-Al films. An increase in the width of the Al (111) peak and an offset of the fiber axis from the substrate normal of 5–8° was observed in the Λ = 333 nm films prepared by using Al–1.0 wt% Cu. The decrease in texture on addition of Cu to Al was attributed primarily to an increase in interlayer roughness as a consequence of reduction in the Al(Cu) grain size. These observations were interpreted in the context of structure zone and dynamic roughness models of film growth.

The metalorganic chemical vapor deposition of very thin (<50 nm) Pb(Zr,Ti)O3 (PZT) thin films was performed for high density (>32 mega bit) ferroelectric memory devices. The growth temperatures were set between 450 and 530 °C to obtain a smooth surface morphology and prevent damage to the underlying reaction barrier layer. The average grain size of a 50-nm-thick film on a Pt electrode was about 34 nm with a size distribution (σ2) of 11 nm. These values are much smaller than the sol-gel-derived PZT films (55 and 25 nm, respectively). Very thin films with a thickness of approximately 30 nm were prepared at wafer temperatures ranging from 500 to 525 °C. Even with the very small thickness, the films showed good ferroelectric properties with a typical remanent polarization from 10 to 15 μC/cm2 and an extremely low coercive voltage of 0.3 V. However, the leakage current density was rather high resulting in nonsaturating polarization versus voltage curves. Even though good ferroelectric properties were obtained, the formation of PtxPby alloys on top of the Pt electrode was consistently observed. This precludes the reliable control of film composition and electrical performance. The adoption of an Ir electrode successfully eliminated intermetallic alloy formation and resulted in better and reproducible process control. A 50-nm-thick PZT film on an Ir/IrO2/SiO2/Si substrate also showed a reasonable ferroelectric performance.

Glass-ceramics containing a large amount of calcium pyrophosphate (β–Ca2P2O7) crystal were prepared via crystallization and sintering; compacts of a calcium phosphate glass powders with a composition of 60CaO · 30P2O5 · 5TiO2 · 5Na2O (in mol%) were heated for 3–6 h at 850 °C in air. The compacts were densified by the viscous flow of the glassy phases during heating. The calcium phosphate glass-ceramics were found to show a bending strength of approximately 100 MPa, and they were easy to machine, as confirmed by a drilling test using a conventional carbide tool. The machinability is thought to arise from the microstructure consisting predominantly of the interlocking and platelike β–Ca2P2O7 precipitated in the glass.

Plastic instabilities were investigated in an Al–Zn–Mg–Cu alloy by depth-sensing microhardness testing in Vickers geometry. The alloy investigated showed strong age hardening as a consequence of Guiner–Preston zone formation at room temperature. The orientation dependence of the Portevin–Le Chátelier (PLC) effect was investigated by microindentation tests in differently oriented grains. If the direction of the indentation was close to the 〈100〉 crystal axis and the diagonal of the Vickers indenter coincides with the 〈110〉 crystal direction, the PLC effect was more pronounced. Under these conditions the instabilities could be observed even after 5 h of natural aging, while the PLC effect disappeared in grains with other orientations after 2 h of aging. The orientation dependence of the indentation curves was observed up to the maximal measured imprint size (d ≈ 80 μm). It is suggested that the initialization of the PLC bands takes place in the close vicinity of indenter/sample contact surface. Considering only a uniaxial compressive stress component in the sample/indenter contact planes, in the vicinity of the indenter single sliplike and multiple sliplike conditions are attained depending on the orientation of the indenter relative to the sample. Changes of the slip conditions correlate with changes in the observation regime of instability which explains the orientation dependence.

Electromigration rates in polycrystalline interconnect lines are controlled by grain-boundary diffusion. As such, reliability of such interconnects is a direct function of the grain-boundary character distribution in the lines. In the present work, drift velocity experiments were performed on multicrystalline lines of pure Al to determine the electromigration activation energy of the lines. Lines cut from films processed by partially ionized beam deposition techniques were analyzed. One set of lines was analyzed in the as-deposited condition while the other film was annealed before testing. The measured drift velocities varied dramatically between these two types of films, as did the grain-boundary character distributions measured by orientation imaging. The data were analyzed based on Borisov's equation to obtain mean grain-boundary energies. Grain-boundary energy of the film with poor electromigration performance was calculated to be that reported for random boundaries, while that for the more reliable film was calculated to be that reported for twin boundaries in Al. Percolation theory was used to aid explanation of the results based upon the fraction and connectedness of special boundaries in the films.

Silicon carbide ceramics with a powder mixture of sialon composition as a densification aid were prepared by hot pressing through a transient liquid phase, and the effects of sintering atmosphere and starting phases on the microstructural characteristics were investigated. The sintered SiC with the additive of a Y–α-sialon composition in argon showed high sintered density and grains with large aspect ratio. But sintered specimens in nitrogen yielded grains with low aspect ratio and small grain size, because of the retardation of phase transformation and grain growth. The SiC specimen prepared from the starting β–SiC powder with Y–α-sialon composition showed the highest fracture toughness of approximately 6.0 MPa m1/2.

An experimental and theoretical approach has been described for the determination of the strength of partially aligned discontinuous fiber-reinforced composites. The fiber alignment information was obtained as a Gaussian or normal distribution function by using an x-ray-diffraction technique. The distribution function was then used in the composite strength equation to calculate the theoretical strength. This approach was applied to a composite of vapor grown carbon fiber (VGCF) in a polypropylene matrix, and the experimental and theoretical results were compared. As expected, the composite strength increased with increase in fiber volume fraction and the degree of fiber alignment. It was also observed that the composite strength was sensitive to variation in fiber length when the average fiber length was less than the critical fiber length. At higher fiber volume fractions the composite strength was much lower than predicted by theory. This is most likely due to incomplete wetting and infiltration of the VGCF.

High-temperature fracture behavior of a Yb2O3–SiO2–doped hot-pressed silicon nitride (Si3N4) ceramic was investigated in four-point flexure between 1000 and 1500 °C at five crosshead speeds, using the specimens precracked with three indentation loads. Above 1000 °C, a temperature and stressing rate dependence of fracture stress was seen. At 1200 °C the fracture stress of the precracked specimens increased with decreasing stressing rates due to a toughening effect, the absence of slow crack growth (SCG). However, at 1400 and 1500 °C the fracture stress decreased with decreasing stressing rate. In particular, this dependence was stronger at 1500 °C than at 1400 °C. The SCG was observed only in the specimens precracked with indentation loads of 98 and 196 N. This crack extended with increasing test temperature and/or decreasing stressing rate. The dependence of fracture stress on stressing rate was attributed to a SCG behavior at higher temperatures.