The film stress evolutions induced by the phase transformation of Sn/Ni(P) films during thermal treatment were investigated using an in situ measurement of wafer curvature by laser scanning. Apparently, tensile stress developed due to the layer-by-layer formation of Ni3Sn4 and Ni3P phases for Sn/Ni(11.7P) films, and a compressive stress evolved for Sn/Ni(3P) films, despite the same phase transformation. The molar volume mismatch and x-ray diffraction analyses before and after the reaction between Sn and Ni(P) films suggested that a compressive stress existed in the Ni3Sn4 layer while the Ni3P layer was under a tensile stress state. The apparent stress states (tensile or compressive) for overall thickness of the films formed by the layer-by-layer transformation in Sn/Ni(P) were determined by the competition between compressive stress related to Ni3Sn4 formation and tensile stress caused by Ni3P formation. The stress states were dependent upon the relative thickness of the product layers with varying P content.

In this paper, a new method for the identification of material parameters is presented. Neural networks, which are trained on the basis of finite element simulations, are used to solve the inverse problem. The material parameters to be identified are part of a viscoplasticity model that has been formulated for finite deformations and implemented in the finite element code ABAQUS. A proper multi-creep loading history was developed in a previous paper using a phenomenological model for viscoplastic spherical indentation. Now, this phenomenological model is replaced by a more realistic finite element model, which provides fast computation and numerical solutions of high accuracy at the same time. As a consequence, existing neural networks developed for the phenomenological model have been extended from a power law hardening with two material parameters to an Armstrong–Frederick hardening rule with three parameters. These are the yield stress, the initial slope of work hardening, and maximum hardening stress of the equilibrium response. In addition, elastic deformation is taken into account. The viscous part is based on a Chaboche-like overstress model, consisting of two material parameters determining velocity dependence and overstress as a function of the strain rate. The method has been verified by additional finite element simulations. Its application for various metals will be presented in Part II, [J. Mater. Res.21, 677 (2006)].

Electrostatic potentials within a core/shell nanowire structure, composed of an intrinsic germanium core surrounded by its oxide and a heavily doped germanium shell, were investigated by electron holographic analysis on its cross-section. The potential distribution resulting from interface charges as well as dopants was successfully imaged. The surface potential, screening length, and doping concentration for the heavily doped germanium shell were determined quantitatively from the potential image. These characteristics were compared with values obtained from a numerical solution of Poisson's equation.

The oxidation of both single crystal and relatively pure polycrystalline silicon carbide, between 973 and 2053 K, resulted in the formation of cristobalite, quartz, or tridymite, which are the stable crystalline polymorphs of silica (SiO2) at ambient pressure. The oxide scales were found to be pure SiO2 with no contamination resulting from the oxidizing environment. The only variable affecting the occurrence of a specific polymorph was the oxidation temperature. Cristobalite was formed at temperatures ≥1673 K, tridymite between 1073 and 1573 K, and quartz formed at 973 K. The polymorphs were determined using electron diffraction in a transmission electron microscope. These results were further confirmed using infrared and Raman spectroscopies. Cristobalite was observed to grow in a spherulitic fashion from amorphous silica. This was not the case for tridymite and quartz, which appeared to grow as oriented crystalline films. The presence of a thin silicon oxycarbide interlayer was detected at the interface between the SiC substrate and the crystalline silica using x-ray photoelectron spectroscopy.

Gd-doped ceria solid solutions have been recognized to be leading electrolytes for use in intermediate-temperature fuel cells. In this paper, the preparation, solubility, and densification of Gd0.1Ce0.9O1.95 ceramics derived from carbonate co-precipitation are reported. The dissolution of Gd2O3 in CeO2 lattice was identified to be completed during the co-precipitation process by studying the lattice parameter as a function of temperature. After calcination at 800 °C for 2 h, the nano-sized Gd0.1Ce0.9O1.95 powder (∼33 nm) with a nearly spherical shape and a narrow particle-size distribution was obtained. This calcined powder has high sinterability and maximum densification rate at ∼1000 °C. Sintering at 1300 °C for 4 h yielded over 97% relative density with near maximum. The grain size increased with increases in sintering temperature. The ionic conductivity of these pellets was tested by alternating current impedance spectroscopy to elucidate the contribution of intragranular and intergranular conductivity to the total ionic conductivity. It was found that sintering temperature does not affect intragranular conductivity, though intergranular conductivity was strongly influenced by grain size, grain boundary area, and relativity density. This pellet sintered at 1500 °C for 4 h showed a high ionic conductivity of 5.90 × 10−2 s/cm when measured at 750 °C. The characterization and structural evaluation of the as-received powders were carried out using x-ray diffraction, transmission electron microscopy, Brunauer–Emmett–Teller, and dilatometer and impedance analysis.

We report a detailed study of the grain orientations and grain boundary (GB) networks in YBa2Cu3O7-δ (YBCO) films ∼0.8 μm thick grown by both the in situ pulsed laser deposition (PLD) process and the ex situ metalorganic deposition (MOD) process on rolling-assisted biaxially textured substrates (RABiTS). The PLD and MOD growth processes result in columnar and laminar YBCO grain structures, respectively. In the MOD-processed sample [full-width critical current density Jc(0 T, 77 K) = 3.4 MA/cm2], electron back-scatter diffraction (EBSD) revealed an improvement in both the in-plane and out-of-plane alignment of the YBCO relative to the template that resulted in a significant reduction of the total grain boundary misorientation angles. A YBCO grain structure observed above individual template grains was strongly correlated to larger out-of-plane tilts of the template grains. YBCO GBs meandered extensively about their corresponding template GBs and through the thickness of the film. In contrast, the PLD-processed film [full width Jc(0 T, 77 K) = 0.9 MA/cm2] exhibited nearly perfect epitaxy, replicating the template grain orientations. No GB meandering was observed in the PLD-processed film with EBSD. Direct transport measurement of the intra-grain Jc(0 T, 77 K) values of PLD and MOD-processed films on RABiTS revealed values up to 4.5 and 5.1 MA/cm2, respectively. As the intra-grain Jc values were similar, the significantly higher full-width Jc for the MOD-processed sample is believed to be due to the improved grain alignment and extensive GB meandering.

Elastic-viscoelastic correspondence was used to generate displacement–time solutions for spherical indentation testing of soft biological materials with time-dependent mechanical behavior. Boltzmann hereditary integral operators were used to determine solutions for indentation load-relaxation following a constant displacement rate ramp. A “ramp correction factor” approach was used for routine analysis of experimental load-relaxation data. Experimental load-relaxation tests were performed on rubber, as well as kidney tissue and costal cartilage, two hydrated soft biological tissues with vastly different mechanical responses. The experimental data were fit to the spherical indentation ramp-relaxation solutions to obtain values of short- and long-time shear modulus and of material time constants. The method is used to demonstrate linearly viscoelastic responses in rubber, level-independent indentation results for costal cartilage, and age-independent indentation results for kidney parenchymal tissue.

One-dimensional α-MnO2 nanowires with a controlled width of 10–20 nm have been developed by means of ultrasonic waves from mesoporous carbon using KMnO4 as the precursor. The formation mechanism has been proposed based on the results. A peak around 100 K was detected in the temperature-dependence of magnetization curve, indicating the ferromagnetic state in nanocomposite mesoporous carbon-MnO2, which is in agreement with the transition temperature found from the magnetization versus applied magnetic field curve. The magnetization versus temperature curve of the obtained MnO2 nanowires showed a magnetic transition at about 50 K, illustrating that a parasitic ferromagnetic component is composed on the antiferromagnetic structure of MnO2. The advantage of the method reported here is that phase-controlled synthesis of α-MnO2 nanowires was implemented regardless of pH, temperature, and types of ions in the reaction system. A major advantage of this approach is the efficient, fast, and reproducible control of width and the facile strategy to synthesize nanowires MnO2, in addition to the high purity of the resultant material.

Well-structured and monodisperse nanocomposite spheres with a magnetic core/mesoporous silica shell structure (MCMS) were obtained. The effects on the structure and morphology of the MCMS spheres were investigated under various synthesis conditions, including reaction time, quantity of silicate sources of tetraethoxysilane (TEOS) and n-octadecyltrimethoxysilane (C18TMS), ratio of TEOS/C18TMS, and ratio of H2O/EtOH in the starting solution. The particle size of the MCMS spheres and pore diameter are tunable in a certain range with 100% yield. A synthesis mechanism of the mesoporous silica shell was proposed that proceeds via three main stages. The silica shell proved to be effective on protecting the cores from leaching out in acidic conditions.

Because of the applications for W/Cu composite materials in high technology, the advantages of synthesizing this alloy by the hydrogen reduction route were investigated, with special attention to the properties of the product that was formed. Kinetic studies of reduction indicated that the mechanism changes significantly at 923 K, and the product had unusual properties. In the present work, morphological studies of the W/Cu alloy with 20 wt% Cu, produced at 923 K, were carried out by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. The structural studies performed by XRD indicated that, at 923 K, Cu dissolved in W, forming a metastable solid solution in the nanocrystalline state. The samples produced at higher as well as lower temperatures, on the other hand, showed the presence of two phases, pure W and pure Cu. The SEM results were in agreement with the XRD analysis and confirmed the formation of W/Cu alloy. TEM analysis results confirmed the above observations and showed that the particle sizes were about 20 nm. The structure of the W/Cu alloy produced in the present work was compared with those for pure Cu, produced from Cu2O produced by hydrogen reduction under similar conditions. This indicated that the presence of W hinders the coalescence of Cu particles, and the alloy retains its nano-grain structure. The present results open up an interesting process route toward the production of intermetallic phases and composite materials under optimized conditions.

Deformation and fracture of a columnar-grained, ∼1.3-μm-thick TiN coating on a stainless steel substrate was investigated using a spherical tipped conical indenter of 5-μm nominal tip radius. Structural analysis, performed with the support of focused ion beam (FIB) milling and imaging techniques, revealed that the microstructure of the TiN coating had a strong influence on the deformation behavior of the coating. Intergranular sliding in the coating, as well as plastic flow in the ductile substrate, was found to be the predominant processes during the indentation. Neither plastic deformation, in the form of plastic flow, within the coating nor delamination of the interface was observed. Coating deformation was observed to be controlled by the intergranular shear cracking and thus by the interfacial columbic frictional stress between columnar grains. An indentation-energy based model was developed, which deconvolutes the coating behavior from that of the substrate, allowing quantification of the intergranular sliding stress.

Sn, Sn-Sb, Ti, Ce, Zr, Zn, In, In–Sn, and Fe oxides of nanometric size were obtained through the hydrolytic route, starting from molecular precursors in the presence of starch. Gels were treated with α-amylase to produce oxide suspensions and starch degradation. Solid oxide products resulted from reaction with H2O2, washing with H2O, and centrifugation of the suspensions. The nanometric size and morphology of crystallites were assessed by x-ray diffractometry, transmission electron microscopy, and, for SnO2, solid-state nuclear magnetic resonance. Product consolidation at 600 °C did not produce any noticeable increase in dimensions. Thermal analysis coupled with mass spectrometry of evolved gaseous species showed that glucoside residues remain chemically bonded to the nanoparticles, thus explaining the effective stabilization of crystallite dimensions. Aqueous suspensions of nanopowders were mixed with a silicon tetra-ethoxide ethanol solution and subjected to an ordinary sol-gel process. The resulting suspensions were used to obtain stable and homogeneous coatings on glass sheets.

Using concepts of hierarchical multiscale modeling, we report development of a mesoscopic model for single-wall carbon nanotubes with parameters completely derived from full atomistic simulations. The parameters in the mesoscopic model are fit to reproduce elastic, fracture, and adhesion properties of carbon nanotubes, in this article demonstrated for (5,5) carbon nanotubes. The mesoscale model enables modeling of the dynamics of systems with hundreds of ultralong carbon nanotubes over time scales approaching microseconds. We apply our mesoscopic model to study self-assembly processes, including self-folding, bundle formation, as well as the response of bundles of carbon nanotubes to severe mechanical stimulation under compression, bending, and tension. Our results with mesoscale modeling corroborate earlier results, suggesting a novel self-folding mechanism, leading to creation of racket-shaped carbon nanotube structures, provided that the aspect ratio of the carbon nanotube is sufficiently large. We find that the persistence length of the (5,5) carbon nanotube is on the order of a few micrometers in the temperature regime from 300 to 1000 K.

Ferroelectric domain patterning with an electron beam is demonstrated. Polarization of lead zirconate titanate thin films is shown to be reoriented in both positive and negative directions using piezoresponse force and scanning surface potential microscopy. Reorientation of the ferroelectric domains is a response to the electric field generated by an imbalance of electron emission and trapping at the surface. A threshold of 500 μC/cm2 and a saturation of 1500 μC/cm2 were identified. Regardless of beam energy, the polarization is reoriented negatively for beam currents less than 50 pA and positively for beam currents greater than 1 nA.

A hydroxyapatite-gelatin nanocomposite system has been developed to resemble the composition and ultrastructure of natural bone for the application of tissue engineering. In the current study, variations in composition—content of gelatin and glutaraldehyde crosslinker—were examined in the context of mechanical properties and material biocompatibility. It was found that increasing the gelatin concentration resulted in a decreased hydroxyapatite crystal length and was associated with a slight increase in elastic modulus. Increases in gelatin and glutaraldehyde content were associated with increased material fracture toughness. Cellular biocompatibility tests, including cellular attachment and proliferation assays, were also used to assist in the process of optimizing gelatin and glutaraldehyde content. Optimized biomimetic nanocomposite materials for in vivo applications will likely be a compromise between the improved mechanical properties and decreased cytocompatibility associated with increased glutaraldehyde contents.

Highly porous films of titania composed of nanoparticle aggregates were synthesized via gas-to-particle conversion and particle-precipitated chemical vapor deposition. The films were annealed in air for 12 h at temperatures ranging from 400 to 1000 °C. Atomic force microscopy was used to determine the Young's modulus and hardness of both the as-synthesized and annealed films. The Young's modulus and hardness of the as-synthesized films were 4.0 ± 0.4 MPa and 0.026 ± 0.003 MPa, respectively. There was no significant change in either modulus or hardness upon annealing until the films were annealed at a temperature of 1000 °C. The Young's modulus and hardness of these films were 56 ± 6 MPa and 0.10 ± 0.01 MPa, respectively. Results from dynamic light scattering measurements of aggregate size and surface area measurements suggest that annealing at 1000 °C leads to increased networking between distinct nanometer-scale titania aggregates, which strengthens the film.

The microstructure of Ba[Mg1/3(NbxTa(4−x)/4)2/3]O3 ceramics (x = 1, 2, 3, and 4) was investigated. Ordered structure and domain boundary were observed by high-resolution transmission electron microscopy. The disordered structure of 0.41 nm lattice modulation and the 1:2 ordering structure of 0.71 nm lattice modulation in the [111] direction are both formed in Ba[Mg1/3(NbxTa(4−x)/4)2/3]O3 ceramics. Except for the incoherent interface between disordered and 1:2 ordering domain, the coherent interface between two 1:2 ordering domains can also be observed in the Ba[Mg1/3(NbxTa(4−x)/4)2/3]O3 ceramics. In the Ba[Mg1/3(Nb1/4Ta3/4)2/3]O3 ceramic, the formation of an extra ordering structure (lattice modulation of 1.24 nm in the [111] direction) on the antiphase domain boundary with proper Nb substitution contributes to lower dielectric loss due to the stabilization of the domain boundary.

In this paper, we describe the application of thin film combinatorial deposition methods to systematically control the microstructure of AlxSi(1−x) alloys through variations in composition and growth temperature. Discrete libraries of compositionally graded films have been sputter deposited onto silicon substrates to produce two structural phase regions: amorphous a-(Al–Si) and amorphous a-Si plus crystalline c-Al. The microstructure was investigated using x-ray diffraction while atomic force microscopy techniques were used to obtain surface morphology and phase distribution.

Interfacial reactions of Sn-Cu alloys with Ni substrate at 250 °C have been investigated by varying the Cu contents from 0.3wt%Cu to 3.0wt%Cu. The Cu6Sn5 phase is not found in the Sn-0.3wt%Cu/Ni couple. The interfacial reaction sequence of the Sn-0.6wt%Cu/Ni couple is similar to that of the Sn-0.7wt%Cu/Ni. The reaction follows Cu6Sn5 formation stage, growth stage, detachment stage, Cu6Sn5 layer continuing growth stage, Ni3Sn4 formation stage, Cu6Sn5 phase dissolution stage, Ni3Sn4 detachment stage, and Ni3Sn4 phase dissolution stage. Similar results are found for the couples prepared with higher Cu contents, 0.8wt%Cu, 1.0wt%Cu, 2.0wt%Cu, and 3.0wt%Cu, but the detachment positions are different. For the couples with higher Cu-content, the layer detaches at the Cu6Sn5/Ni interface; however, for the 0.6wt%Cu and 0.7wt%Cu couples, the Cu6Sn5 phase layer fractures and detachment occurs inside the layer. Morphologies of the Cu6Sn5 phase are also found to change with Cu contents: the pyramidal shape in the 0.3wt%Cu couple changes to the rod-shape in the 0.8wt%Cu couple, and becomes a very fine rod shape in the 2.0wt%Cu couple.

Pr-doped ZnO phosphor powders were prepared by dry reaction within evacuated sealed silica glass tube. Pr2O3 and Pr6O11 were used as additives. Pr concentrations were 0.5, 1, 3, and 5 mol%, and the sintering temperatures were 600, 800, and 1000 °C, respectively. Photoluminescence (PL) and PL excitation (PLE) spectra were measured to study luminescent properties of samples. Some samples showed the enhancement of green emission. This emission is related to native defects in ZnO. Based on the results of PL and PLE, the origin of the enhancement was discussed in view of native defects in ZnO and the defect-related complex in ZnO varistor ceramics. The possible origin is the increase of native defects such as VZn, OZn, and the complex in the vicinity of grain boundaries and ZnO matrix near the surface of grains. The increase of native defects and the complex are probably due to the existence of the Pr3+-ions with binding to native defects, which form the complex by Coulombic potential.