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A process suitable for preparing metal-insulator-metal thin film capacitors with submicron insulating layers and top electrodes with cm-scale dimensions is presented. Most importantly, this process does not require sophisticated deposition equipment or a clean room environment. The key to large area yield is co-firing the insulator film with a non-dewetting electrode during the dielectric crystallization/densification anneal. We propose a mechanism of electrode dewetting during the high temperature anneal where the metal laterally retreats from geometric asperities that compromise the integrity of the insulating layer. This behavior is driven by surface energy minimization, which promotes metal migration away from the regions of high curvature. This methodology is not material specific, and only requires a top electrode with a large contact angle to the dielectric in question. Using this technique, functional thin film capacitors with 2.5 cm lateral dimensions and 1 μm dielectric thicknesses can be routinely prepared.
The effect of process parameters on the plasma deposition of μc-Si:H solar cells is reviewed in this article. Several in situ diagnostics are presented, which can be used to study the process stability as an additional parameter in the deposition process. The diagnostics were used to investigate the stability of the substrate temperature during deposition at elevated power and the gas composition during deposition at decreased hydrogen dilution. Based on these investigations, an updated view on the role of the process parameters of plasma power, heater temperature, total gas flow rate, and hydrogen dilution is presented.
P- and n-type conductivity domains in dual-doped ZnO:As+N layers grown by metal organic vapor phase epitaxy on GaN–sapphire templates were electrically microcharacterized by scanning capacitance microscopy (SCM) and scanning surface potential microscopy (SSPM) techniques with respect to their defect states. The p-type domains were found to be dominated by two acceptors with thermal activation energies of about 80 and 270 meV, as observed by transient SCM scans at different temperatures. Optically excited SSPM scans revealed defect-to-band transitions at 400, 459, and 505 nm omnipresent in both domain types as well as a shallower transition at 377 nm exclusively in the p-type regions. According to the similar energy levels, the optical transitions at 377 and 400 nm are assigned to acceptor states, whereby the 80-meV acceptor is probably responsible for the conversion from n- to p-type regions in the domains.
A combined structure/property investigation is performed to understand the catalytic effect of TiF3 additive on the absorption/desorption reactions of MgH2. It was found that both TiH2 and MgF2 phases identified by x-ray diffraction cannot explain the observed kinetic enhancement in the MgH2–TiF3 system, whether they are incorporated in a direct or an in situ manner. In combination with the comparative investigation on the catalytic activity of TiF3 and its analog TiCl3, as well as the samples milled under inert and reactive atmospheres, we propose that the catalytically active species is a multicomponent metastable phase composed of host Mg, transition metal Ti, and F anion, the catalytic activity of which is dependent on its interaction with the surrounding chemical environment.
Mixed metal oxide catalysts with nominal compositions of In2Ti1–xFexO5–δ, In2Ti1–xCrxO5–δ, where 0.0 ≤ x ≤ 0.2, have been synthesized by the ceramic route and characterized using the powder x-ray diffraction technique. The In2Ti1–xFexO5–δ samples were single-phase compositions, isomorphic with In2TiO5 phase. The particle size of the In2Ti1–xFexO5–δ samples was lower compared to the parent In2TiO5 oxide. Thermal stability (by thermogravimetry-differential thermal analysis) in varying atmospheres, and temperature-programmed reduction (TPR)/temperature-programmed oxidation cycles have been recorded to investigate their redox behavior as a function of the value of x in this study. The amount of H2 consumed under TPR curves was correlated with the nonstoichiometry generated in the In2Ti1–xFexO5–δ samples. Fe substitution induced ease in the reducibility (i.e., maximum temperature) of the substituted oxides compared to that in In2TiO5. X-ray photoelectron spectroscopy has been used to confirm the oxidation states of indium and other metal ions in fresh and reduced samples.
NixCo1−xO/ZrO2(CaO) directionally solidified eutectics (DSEs) form a ductile metallic interphase after they are chemically reduced at high temperatures. Vickers indentation tests have previously shown a significant change in the crack propagation behavior of the reduced composites due to plastic deformation and strain energy absorption mechanisms operating in the system after reduction. This paper focuses on structural and chemical characterization of NixCo1−xO/ZrO2(CaO) DSEs after reduction. Analytical transmission electron microscopy techniques such as energy dispersive x-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS) show elimination of oxygen and formation of nanoscale Ni(Co) solid.
The objective of this study is to investigate the corrosion susceptibility of surgical AZ91 magnesium alloys in simulated body fluids (SBFs) consisting of bovine serum albumin (BSA) and acidic SBFs (pH 5) using electrochemical methods. The addition of BSA significantly moves the open-circuit potential toward a more positive value and suppresses the corrosion reaction. The corrosion resistance under the open-circuit conditions in the SBFs with 1 g/L BSA is approximately twice that in the SBFs. A higher BSA concentration decreases the corrosion susceptibility. In addition, the acidic SBF results in a higher alloy dissolution rate. The possible mechanisms are discussed.
The morphology of ZnO submicron crystals formed in a weak alkaline environment (pH value less than 11.0) was systematically studied for the first time. ZnO submicron particles with different morphologies (flowers, rod, and wire) were synthesized from an aqueous solution by adopting ethylenediamine as the source of hydroxyl group, hexamethylenetetramine (HMT) as the additive, and potassium chloride (KCl) as the background electrolyte. The effects of primary experimental parameters such as HMT and KCl addition, precursor concentration, and reaction temperature on the microstructure, crystallinity of the resultant particles, and their distribution on substrate are discussed in this paper. In the flowerlike structure, the particle size is more controlled by the precursor concentration, and the microstructure is modulated by increasing the concentration of HMT and the reaction temperature. The introduction of ZnO seed layer on substrate promotes even distribution of ZnO flowers. High concentration KCl electrolyte inhibits formation of the flowerlike structure and promotes the growth of submicron ZnO crystals in rod or wire shape. Mechanism studies indicate that the degree of supersaturation of Zn(OH)2 and the adsorption of organic/inorganic species on the surface of ZnO are the prime factors influencing the nucleation, growth rate, and eventual morphology.
(Pb1−xCax)TiO3 perovskite thin films with nominal compositions of (Pb0.76Ca.24)TiO3 (ferroelectric) and (Pb0.50Ca0.50)TiO3 (relaxor-ferroelectric) were prepared on silicon substrates at low temperatures compatible with those used in Si-technology. The technique used for the processing of these films was ultraviolet (UV) sol-gel photoannealing, using photo-sensitive precursor solutions and UV-assisted rapid thermal processing. The UV-irradiation and thermal treatment of the solution-derived films (gel films) were carried out in air or in oxygen. In both cases, the formation of the perovskite occurred at the same temperature, and this temperature increased as the Ca2+ content increased. Thus, full-perovskite films of (Pb0.76Ca.24)TiO3 were obtained at 723 K whereas those of (Pb0.50Ca0.50)TiO3 were formed at 773 K. Well-defined ferroelectric hysteresis loops were measured in the (Pb0.76Ca.24)TiO3 films, with values of remanent polarization of Pr ∼ 11 μC cm−2 and coercive fields for the films processed in oxygen lower than those of the films processed in air, Ec ∼ 164 and ∼226 kV.cm−1, respectively. These films showed a ferro-paraelectric transition at close temperatures of Tmax ∼ 605 K, although with higher values of the permittivity for the film processed in oxygen, k ∼ 567 at 10 kHz. The (Pb0.50Ca.50)TiO3 films had a diffuse ferro-paraelectric transition with a relaxor-like character, also with higher k values for the films prepared in oxygen, k ∼ 179 at Tmax ∼ 20 K. The possible use of these materials in silicon integrated multifunctional devices is discussed in this paper.
A series of wormhole-like mesoporous borosilicate glasses (MBSGs) with different compositions has been prepared by a combination of surfactant templating, sol-gel methods, and evaporation-induced self-assembly processes. Small-angle x-ray diffraction, high-resolution transmission electron microscopy, and N2 sorption isotherms analysis showed that all the MBSGs prepared possess the mesoporous structure. However, the stability of the mesoporous structure is strongly affected by the boron contents. When boron content was increased, boric acid was found in the final product, and the mesoporous structure was partially degraded. The formation and loss of boric acid through the whole process may account for the partial collapse of the mesostructure.
Replication of metallic high-aspect-ratio microscale structures (HARMS) by compression molding has been demonstrated recently. Molding replication of metallic HARMS can potentially lead to low-cost fabrication of a wide variety of metal-based microdevices. Understanding the mechanics of metal micromolding is critical for assessing the capabilities and limitations of this replication technique. This paper presents results of instrumented micromolding of Al. Measured molding response was rationalized with companion high-temperature tensile testing of Al using a simple mechanics model of the micromolding process. The present results suggest that resisting pressure on the mold insert during micromolding is governed primarily by the yield stress of the molded metal at the molding temperature and a frictional traction on the sides of the insert. The influence of strain rate is also considered.
The influence of annealing on the structural changes and the mechanical properties of Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit-1) bulk metallic glass was systematically studied by varying the annealing times at 703 K. The evolution of the structural state at a relatively high temperature within the supercooled liquid region was studied by thermal analysis, x-ray diffraction, high-resolution transmission electron microscopy, extended x-ray absorption fine structure, and dilatometric measurements. The deformation behavior and the mechanical properties were also examined by carrying out hardness and compression tests for the specimens annealed for various times.
The photophysical properties of MSnO3 (M = Ca, Sr, and Ba) including optical absorption, photoluminescence, and energy band structure including band edge positions were investigated experimentally and theoretically in association with their photocatalytic properties. Photocatalytic reactions for H2 and O2 evolution in the case of sacrificial reagents were performed under ultraviolet (UV) light irradiation. The order of the activities of H2 evolution was CaSnO3 > SrSnO3 > BaSnO3, agreeing not only with that of the conduction-band edges (or band gaps) but also with that of the transferred excitation energy, while that of O2 evolution was CaSnO3 < SrSnO3 < BaSnO3, consistent with that of the angle of the Sn–O–Sn bonds as well as the delocalization of excited energy. When loaded with RuO2 cocatalyst, both CaSnO3 and SrSnO3 can efficiently split pure water into hydrogen and oxygen in a stoichiometric ratio under UV light irradiation. In addition, RuO2-loaded SrSnO3 showed higher water splitting activity than RuO2-loaded CaSnO3 did. This is attributed to the suitable conduction and valence band edges and to high mobility of the photogenerated charge carriers caused by the proper distortion of SnO6 connection in SrSnO3. The RuO2-loaded BaSnO3 photocatalyst cannot split pure water, which might be because of a high concentration of defect centers such as Sn2+ ions and the probability of radiative recombination in BaSnO3.
We report on the synthesis and surface characterization of thin-film nanocomposites using functionalized single-walled carbon nanotubes (CNTs) with a diamine-terminated oligomeric poly(ethylene glycol) [poly(ethylene glycol) bis (3-aminopropyl)-terminated 1500]. The functionalized CNT samples are soluble in highly polar solvents. Their common solubility allows for the intimate mixing of the functionalized nanotubes with the matrix polymer–poly(vinyl alcohol) by dip coating and wet casting to form nanocomposite thin films. We demonstrate the alignment of the CNT bundles in the thin films that are formed without the external field forces. We present our results and discuss alignment reorientations from the characterizations of the nanocomposite thin films by using a Raman spectrometer, scanning electron microscopy, and atomic force microscopy.
Varying amounts of Zn (1, 3, and 7 wt%) were added to Sn–3.5Ag solder on a Cu pad, and the resultant solder joint microstructures after a reflow and isothermal aging (150 °C, up to 500 h) were investigated using scanning electron microscopy, energy dispersive x-ray, and x-ray diffraction, which were subsequently correlated to the results of microhardness and drop tests. Zinc was effective in improving the drop resistance of Sn–3.5Ag solder on the Cu pad, and an addition of 3 wt% Zn nearly doubled the number of drops-to-failure (Nf). The beneficial role of Zn was ascribed to suppression of Cu6Sn5 and precipitation of Zn-containing intermetallic compounds (IMCs). However, the Zn effect was reduced as Cu6Sn5 and Ag3Sn precipitated in a joint IMC layer after prolonged aging. The interface between Ag5Zn8 and Cu5Zn8 was resistant to drop impact, but two other layered IMC structures of Cu6Sn5/Cu3Sn and Cu5Zn8/Cu6Sn5 were not.
The size distribution and morphology of particles (dense or hollow) produced from polydispersed droplets in spray pyrolysis were studied both experimentally and theoretically. Zirconia, generated from a zirconyl hydroxychloride precursor, was selected as a model material. The simulation method that was previously developed by our group [J. Mater. Res., 15, 733 (2000)], in which droplets were assumed to be uniform, was improved to evaluate the effect of polydispersity in droplets on the size and morphology of the resulting particles. Simultaneous equations for heat and mass transfer of solvent evaporation and solute mass transfer inside droplets were solved numerically for a number of discrete classes of droplet size distribution. The role of the decomposition reaction was also included after the evaporation stage of polydispersed droplets in an attempt to explain the densification of particles. In hollow particle generation, this simulation was used to evaluate the thickness of a particle shell. The experimental results were in good agreement with the simulation data, suggesting that the model provides a more realistic prediction.
The growth of HfO2 thin films on a HF-dipped p-Si(100) substrate at 200 °C by atomic-layer deposition (ALD) using Hf[N(C2H5)(CH3)]4 and H2O vapor as precursors is demonstrated. Uniform HfO2 thin films are obtained on a 4-in. silicon wafer, and the energy-band gap and band offset are determined by x-ray photoelectron spectroscopy analysis. The as-deposited HfO2 thin film is amorphous and able to crystallize at 500 ∼ 600 °C with only the monoclinic phase. As for the electrical performance of Au–Ti–HfO2–Si metal oxide semiconductor capacitors, a dielectric constant of ∼17.8 and an equivalent oxide thickness value of ∼1.39 nm are obtained from the 40-cycle ALD film after annealing at 500 °C. In addition, the breakdown field is in the range of 5 ∼ 5.5 MV/cm, and the fixed charge density is on the order of 1012 cm−2, depending on the annealing temperatures. The interface quality of HfO2 thin films on silicon is satisfactory with an interface-trap charge density of ∼3.7 × 1011 cm−2 eV−1.
Small-angle scattering (SAS) and ultra small-angle scattering techniques, employing x-rays and neutrons, were used to characterize six different aluminum nanopowders and nanopowders composed of molybdenum trioxide and tungsten trioxide nanoparticles. Each material has different primary particle morphology and aggregate and agglomerate geometry, and each is important to the development of nano-energetic materials. The combination of small-angle and ultra small-angle techniques allowed a wide range of length scales to be probed, providing a more complete characterization of the materials. For the aluminum-based materials, differences in the scattering of x-rays and neutrons from aluminum and aluminum oxide provided sensitivity to the metal core and metal oxide shell structure of the primary nanoparticles. Small-angle scattering was able to discriminate between particle size and shape and agglomerate and aggregate geometry, allowing analysis of both aspects of the structure. Using the results of these analyses and guided by scanning electron microscopy (SEM) images, physical models were developed, allowing for a quantitative determination of particle morphology, mean nanoparticle size, nanoparticle size distribution, surface layer thickness, and aggregate and agglomerate fractal dimension. Particle size distributions calculated using a maximum entropy algorithm or by assuming a log-normal particle size distribution function were comparable. Surface area and density determinations from the small-angle scattering measurements were comparable to those obtained from other, more commonly used analytical techniques: gas sorption using Brunauer–Emmett–Teller analysis, thermogravimetric analysis, and helium pycnometry. Particle size distribution functions derived from the SAS measurements agreed well with those obtained from SEM.
Large-area single-crystalline vanadium dioxide nanoflakes were first fabricated via a thermal reduction method in a tube furnace. The sample was characterized by x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results show that VO2 nanoflakes are single-crystalline with a monoclinic structure. The VO2 nanoflakes have a width of 200–300 nm, a thickness of 50–100 nm, and a length up to 1–2 μm. It is found that single-crystalline VO2 nanoflakes show a novel and complicated 5–7-step Li-storage behavior for an insertion amount of <0.6 mol lithium per mol of VO2.
Amorphization of metallic titanium by ball milling was presented. With the introduction of continuous pickup of impurities, hexagonally close-packed (hcp) titanium transformed gradually into an amorphous phase without experiencing any intermediate stage of forming a detectable metastable compound phase. The crystallization temperature of the obtained Ti metal glassy phase is about 640 K. The total concentration of the impurities (oxygen, nitrogen, iron, etc.) in the final product of the milled powders that was obtained after 60 h of milling was 10.85 at.%. The amorphization of metallic titanium may account for the combined effects of the pickup oxygen impurity in small amount and the Gibbs–Thompson effect.