Dense polycrystalline titania (TiO2, rutile) was converted into oriented arrays of single-crystal titania nanofibers by reaction with a noncombustible, hydrogen-bearing gas mixture at only 680–780 °C. Such nanofiber formation resulted from anisotropic etching (“nanocarving”) of the titania grains. The fibers possessed diameters of 20–50 nm and lengths of up to several microns, with the long fiber axes oriented parallel to the [001] crystallographic direction of rutile. Mass spectroscopy and inductively coupled plasma spectroscopy indicated that oxygen, but not titanium, was removed from the specimen during the reaction with hydrogen. The removal of substantial oxygen and solid volume from the reacting surfaces, without an appreciable change in the Ti:O ratio at such surfaces, was consistent with the solid-state diffusion of titanium cations from the surface into the bulk of the specimen. The reaction-induced weight loss followed a parabolic rate law, which was also consistent with a solid-state diffusion-controlled process.

The authors would like to take this opportunity to rectify a derivational error in our recently published research article. Equation (12) (p. 2824) in the original manuscript pertains to the calculation of the Young's modulus from nanoindentation data considering a Johnson, Kendall, Roberts (JKR) adhesion model:

Subsolidus equilibria in the PbO-poor part of the TiO2–PbO–SiO2 diagram were studied with the aim of investigating possible applications for low-temperature thick-film dielectrics. The tie lines are between PbTiO2 and PbSiO3, and between PbTiO3 and SiO2. The results show that the TiO2, when added to low-temperature softening point glasses, reacts with the PbO from the glass, so forming PbTiO3. These results were applied to a low-temperature firing dielectric, consisting of a lead-rich PbO–SiO2–B2O3 glass filled with a TiO2 powder. The conversion of TiO2 to the PbTiO3 crystalline phase was observed above firing temperatures of approximately 600 °C. The kinetics of the reaction depend on the particle size of the TiO2.

Cancellous bone plays a crucial structural role in the skeleton, yet little is known about the microstructure-mechanical property relationships of the tissue at the microscale. Cancellous tissue is characterized by a microstructure consisting of layers interspaced with transition zones with different proportions of collagen and mineral. In this study, the quasistatic and dynamic mechanical properties of lamellar and interlamellar tissue in human vertebrae were assessed with nanoindentation, and the collagen content and organization were characterized with second harmonic generation microscopy. Lamellar tissue was 35% stiffer, 25% harder, and had a 13% lower loss tangent relative to interlamellar tissue. The stiff, hard lamellae corresponded to areas of highly ordered, collagen-rich material, with a relatively low loss tangent, whereas the compliant, soft interlamellar regions corresponded to areas of disordered or collagen-poor material. These data suggest an important role for collagen in the tissue-level mechanical properties of bone.

This study investigated a mechanism for controlling the shape of Cu nanocrystals fabricated using the polyol process, which considers the thermodynamic transition from a faceted surface to a rough surface and the growth mechanisms of nanocrystals with faceted or rough surfaces. The faceted surfaces were stable at relatively low temperatures because of the low entropy of perfectly faceted surfaces. Nanocrystals fabricated using a coordinative surfactant stabilized the faceted surface at a higher temperature than those fabricated using a noncoordinative surfactant. The growth rate of the surface under a given driving force was dependent on the surface structure, i.e., faceted or rough, and the growth of a faceted surface was a thermally activated process. Surface twins decreased the activation energy for growth of the faceted surface and resulted in rod- or wire-shaped nanocrystals.

Using geometrically constrained specimens, the plastic flow behaviors of the as-cast and the relaxed Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 bulk metallic glass in the dynamic compression were investigated. Both alloys exhibit a significant plasticity in the dynamic compression. The plastic deformation in both alloys is still inhomogeneous, which is characterized by the serrated plastic flow and the formation of shear bands. Free volumes affect the shear banding and the plastic flow. The reduced free volume results in the deviation of the shear banding direction from the maximum shear stress. The relaxed alloy exhibits the obvious stress overshoot, which is consistent with the theoretical prediction using a free volume model.

Bismuth titanate (Bi2Ti2O7) nanotubes were successfully synthesized with an alumina template-based sol-gel technique. As-synthesized nanotubes are smooth and uniform with diameters ranging from 180 to 330 nm and lengths varying from 7 to 12 μm. Extensive characterization of as-prepared samples has been performed using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy-dispersive x-ray spectroscopy (EDS), and selected-area electron diffraction (SAED). Photocatalytic studies indicate that as-prepared nanotubes possess higher photocatalytic activity than the corresponding bulk sample prepared without the use of an alumina template.

The reliability of microelectronic interconnections depends on hot deformation of solders. In this work, we studied the localized stress relaxation of Sn3.5Ag eutectic alloy using the impression testing in the temperature range of 393–488 K. By incorporating the effect of internal stress in the analysis, we obtained the strain rate-stress exponent of 6.59. The activation energy for the stress relaxation is in the range from 38.6 to 43.8 kJ/mol, which compares well with the estimated activation energy of dislocation pipe diffusion, 46 kJ/mol, in pure tin. This suggests that a single mechanism of dislocation climb limited by dislocation pipe diffusion might be the controlling mechanism for the localized stress relaxation of the Sn3.5Ag eutectic alloy.

We developed a methodology for the evaluation of the effective Young's modulus (EYM) of the vertically aligned carbon nanofibers array (CNFA). The carbon nanofibers array is treated in this study as a continuous structural element, and, for this reason, the determined EYM might be appreciably different (actually, lower) than the Young's modulus (YM) of the material of an individual carbon nanotube or a nanofiber. The developed methodology is based on the application of a compressive load onto the carbon nanofibers array, so that each individual carbon nanofiber experiences axial compression and is expected to buckle under the compressive load. The relationship between the applied compressive stress and the induced displacement of the carbon nanofiber array is measured using a table version of an Instron tester. It has been found that the carbon nanofiber array exhibits nonlinear behavior and the EYM increases with an increase in the compressive load. The largest measured EYM of the carbon nanofiber array turned out to be about 90 GPa. It has been found also that the fragmentary pieces of lateral graphitic layer in the carbon nanofiber array resulted in substantial worsening of the quality of the carbon nanofibers. This might be one of the possible reasons why the measured EYM turned out to be much lower than the theoretical predictions reported in the literature. The measured EYM is also much lower than the reported in the literature atomic force microscopy (AFM)-based data for the EYM for multiwalled carbon nanotubes (MWCNTs) that possess uniform and straight graphitic wall structure. Our transmission electron microscope (TEM) observations have revealed indeed poor structural qualities of the plasma-enhanced chemical vapor deposition (PECVD) grown CNFs.

We fabricated three-dimensional photonic crystals by self-assembling gold nanoshells via forced sedimentation method. Gold nanoshells with a diameter of 458 nm (418-nm silica core and 20-nm gold shell) were synthesized and self-assembled into a 5-μm-thick opal structure. We observed reflection peaks at 710 and 1240 nm, which are believed to be from the complete three-dimensional photonic band gap and the (111) directional gap, respectively. Theses results were in good agreement with the photonic band-structure calculations done by the finite-difference time-domain method. Angle-resolved reflectivity measurements were also performed to investigate the existence of the complete three-dimensional photonic band gap.

Control over mechanical properties of hydrogels is of primary importance for the use of these materials in drug delivery and tissue engineering applications. We demonstrate here that crystallinity and block length of poly(lactide) (PLA) can be used to tune the elastic modulus of associative network gels of poly(lactide)–poly(ethylene oxide)–poly(lactide) over several orders of magnitude. Polymers made with crystalline L lactic acid blocks formed very stiff hydrogels at 25 wt% concentration with an elastic modulus that was almost an order of magnitude higher than hydrogels of polymers with a similar molecular weight but containing amorphous D/L-lactic acid blocks. The relaxation behavior and crosslink density of gels are also significantly influenced by crystallinity of PLA and are again a function of PLA block length. Using these variables we can design new tailor-made materials for biomedical applications with precise control over their structure and mechanical properties.

An elementary theory for a rigid spherical indenter contacting a thin, linear elastic coating that is bonded to a rigid substrate was developed. This theory predicts that contact area varies as the square root of the compressive load in contrast to Hertz theory where contact area varies as the two-thirds power of the compressive load. Finite element analysis confirmed an approximate square root dependence of contact area on compressive load when the coating thickness-to-indenter radius ratio is less than 0.1 and when the coating Poisson’s ratio is less than 0.45. Thin-coating contact mechanics theories that use either the Derjaguin-Muller-Toporov (DMT) approximation or the Johnson-Kendall-Roberts (JKR) approximation were also developed. In addition, a finite element simulation capability that includes adhesion was developed and verified. Illustrative finite element simulations that include adhesion were then performed for a thin elastic coating (rigid indenter/substrate). Results were compared with the thin-coating contact theories and the transition from DMT-like to JKR-like response was examined.

Our concern here is to rationalize experimental observations of failure modes brought about by indentation of hard thin ceramic films deposited on metallic substrates. By undertaking this exercise, we would like to evolve an analytical framework that can be used for designs of coatings. In Part I of the paper we develop an algorithm and test it for a model system. Using this analytical framework we address the issue of failure of columnar TiN films in Part II [J. Mater. Res.21, 783 (2006)] of the paper. In this part, we used a previously derived Hankel transform procedure to derive stress and strain in a birefringent polymer film glued to a strong substrate and subjected to spherical indentation. We measure surface radial strains using strain gauges and bulk film stresses using photo elastic technique (stress freezing). For a boundary condition based on Hertzian traction with no film interface constraint and assuming the substrate constraint to be a function of the imposed strain, the theory describes the stress distributions well. The variation in peak stresses also demonstrates the usefulness of depositing even a soft film to protect an underlying substrate.

The addition of Ag to Cu–Zr alloys is very effective for the increase in the stability of supercooled liquid as well as the glass-forming ability (GFA). The large supercooled liquid region (ΔTx) exceeding 60 K in Cu–Zr–Ag ternary system was obtained in a wide range of 25–55 at.% Cu, 40–65 at.% Zr, and 5–25 at.% Ag. The best GFA was obtained around Cu45Zr45Ag10, and glassy alloy rods with diameters up to 6.0 mm were formed by copper mold casting. The bulk glassy alloys exhibit good mechanical properties, i.e., compressive fracture strength of 1780–1940 MPa, Young's modulus of 106–112 GPa, compressive plastic elongation of 0.2–2.9%, and Vickers hardness of 534–599. The finding of the new Cu–Zr–Ag ternary glassy alloy system with high GFA and good mechanical properties is important for development and scientific studies of bulk glassy alloys.

Porous Pd42.5Cu30Ni7.5P20 bulk glassy alloy rods with porosities up to 71% were successfully prepared by water quenching in a 15 MPa hydrogen atmosphere, followed by heat treatment in a supercooled liquid state. Pores with sizes up to 80 μm were homogeneously distributed over the whole cross-sectional area. Under compressive deformation, the porous alloys with porosities exceeding 41% did not show macroscopic fracture in a wide compressive strain range up to 0.6. Mechanical tests with porous alloy rods whose pores are anisotropically oriented indicate that the plasticity of the porous alloy is strongly affected by stress concentration factor.

The creep compliance of viscoelastic materials such as synthetic polymers is an established metric of the rate at which strain increases for a constant applied stress and can, in principle, be implemented at the nanoscale to compare quantitatively bulk or thin film polymers of different structures or processing histories. Here, we outline the evolution of contact creep compliance analysis and application for both conical and spherical indenter geometries. Through systematic experiments on four amorphous (glassy) polymers, two semi-crystalline polymers and two epoxies, we show that assumptions of linear viscoelasticity are not maintained for any of these polymers when creep compliance is measured via conical indentation at the nanoscale, regardless of the rate of stress application (step or ramp). Further, we show that these assumptions can be maintained to evaluate the contact creep compliance Jc(t) of these bulk polymers, regardless of the rate of stress application, provided that the contact strains are reduced sufficiently through spherical indentation. Finally, we consider the structural and physical properties of these polymers in relation to Jc(t), and demonstrate that Jc(t) correlates positively with molecular weight between entanglements or crosslinks of bulk, glassy polymers.

Polycrystalline diamond films are deposited on p-type Si (100) and n-type SiC (6H) substrates at the low surface deposition temperatures of 370 °C–530 °C using a microwave plasma-enhanced chemical vapor deposition system in which the surface temperature during deposition is monitored and controlled. A very high growth rate up to 1.3 μm/h on SiC substrate at 530 °C surface temperature is obtained. The room temperature in-plane thermal conductivity of the low-surface-temperature–deposited thin films is measured by a traveling wave method. The diamond films of grain sizes between 3 and 7 μm and deposited at 370 °C showed a high thermal conductivity value of ∼6.5 W/cm-K, which is much higher than the single crystal SiC thermal conductivity value at room temperature. Diamond films deposited on Si and SiC single crystals at higher temperatures showed even higher thermal conductivities of 11–17 W/cm-K. The structure and microstructure of these films are characterized by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy, and are related to measured thermal conductivities.

TiO2 nanoparticles with embedded magnetite were suspended in aqueous HAuCl4 and ultraviolet irradiated to photodeposit gold on the surface. The degree of gold coating and the wavelength of absorbance could be controlled by adjusting [HAuCl4]. Absorbance maxima were between 540-590 nm. Particles exhibited superparamagnetic properties (blocking temperature ∼170 K) whether or not coated with gold. These particles have potential applications as drug delivery agents, magnetic imaging contrast agents, and magnetically separatable photocatalysts with unique surface properties.

Effective grain alignment in bismuth titanate ceramic was successfully realized by a novel pressure sintering technology, centrifugal sintering, in which centrifugal force is introduced by high-speed rotation of materials during the process of sintering. X-ray diffraction analyses indicated a very high orientation degree with a Lotgering factor f of ∼0.96 in centrifugal sintered samples. Scanning electron micrographs revealed that the platelike grains are well oriented with their c axes parallel to centrifugal force. The mechanism responsible for grain alignment with introduction of centrifugal force was tentatively proposed.