Single-crystalline nanobelts of molybdenum trioxides were grown by direct thermal oxidization evaporation of metal molybdenum foils. Their structures, defects, and optical properties were investigated via x-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), atomic force microscopy, micro-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV-VIS). Single-crystalline nanobelts were identified as an orthorhombic structure with an average stoichiometry of MoO3.02analyzed by energy dispersive spectroscopy of x-rays. The length, width, and thickness of a nanobelt were determined to be parallel to the b, c, and aaxis of the MoO3unit cell, respectively. The thickness of the nanobelt increased by integer multiples of 0.5ain a layer-by-layer fashion during growth. A density of dislocations as high as about 1.2 × 1013cm−2was formed, which may be attributed to relaxation of large strains during cooling. A special dislocation configuration was observed by HRTEM, which was well reproduced by image simulations based on the proposed model. The resulting morphology of nanobelts was proposed to be governed by growth kinetics. Micro-Raman and FTIR spectra were successfully analyzed on the basis of vibration of MoO6octahedra. It was found that micro-Raman spectra were quite dependent on the size of the nanobelts. A band gap energy of 3.04 eV derived from UV-VIS measurements was observed to be red shifted relative to the previously reported experimental values, which may be due to the presence of a high density of defects.

Si1−xGexOynanowire (SiGeONW) assemblies with cord-, chain-, and tubelike morphologies were grown on a Si substrate via the carbothermal reduction of GeO2/CuO powders at 1100 °C in Ar. The growth of various SiGeONWs assemblies follows the vapor-liquid-solid process. The CuSiGe droplets formed during the growth of SiGeONWs simultaneously play the roles of catalyst and reactant. The morphology of SiGeONWs assemblies is not temperature controlled but dependent on the Cu concentration and the size of CuSiGe catalysts. This phenomenon is unlike the Ge- and Ga-catalyzed growth of SiOxnanowire assemblies. In addition, the processing parameters and the mechanisms for the growth of SiGeONWs assemblies with various morphologies are discussed.

Recently, we reported the discovery of new high-aspect ratio titania nanotubes. These nanotubes were synthesized by means of anodization in an oxalic acid electrolyte containing chlorine ions and were found to have significant carbon content. In this article, the synthesis of similar titania nanotubes in oxalic, formic, trichloroacetic, gluconic, hydrochloric, and sulfuric acid is reported. Differences in carbon content and morphology are analyzed, which in turn provides information on the chemistry of the formation of these nanotubes. Our results suggest that the carbon content in the nanotubes can be controlled by the use of an appropriate organic acid.

A longer lifespan is still being sought for biomaterials used for joint repair. We developed a new nanocomposite material of polytrimethylene carbonate (PTMC), hydroxyapatite (HAP), and multiwalled carbon nanotubes (MWNT) to mimic real cartilage. Experimental results were compared with those of natural cartilage and the conventional joint replacement material ultrahigh-molecular-weight polyethylene (UHMWPE). Friction experiments showed that our developed composite material had a coefficient of friction close to that of articular cartilage. Nanoindentation experiments indicated that the surface elastic behavior was similar to that of cartilage. The surface attraction forces on a silicon atomic force microscope tip were much higher for cartilage than those for the other two materials. These results hold promise for this artificial cartilage composite material’s performance in vivo, following further experimental investigations and chemical modifications.

Results of the mechanical alloying of binary Mg–Ti and ternary Mg–Ti–Ni mixtures using two different process control agents are reported. Both high- and low-energy milling resulted in the formation of cubic compounds. When all starting reactants had disappeared, a mixture of two face-centered cubic (fcc) phases was formed with lattice constants around 4.40 and 4.25 Å. The electrochemical hydrogen storage capacity, 450 mAh/g for (Mg0.65Ti0.35)0.95Ni0.05, was about one-third that reported for Mg–Ti thin films. This suggested that only one of the two fcc phases was active at ambient conditions. Prolonged mechanical alloying of (Mg0.60Ti0.40)0.95Ni0.05resulted in full conversion of the material into one fcc-phase with a very small crystallite size, an intermediate lattice constant (4.33 Å), and a sharply decreased storage capacity.

A thermogravimetric method was used to analyze intermediate processes involved in the formation and decomposition of AgNbO3and AgTaO3perovskites. Critical parameters that control the kinetics of the formation are associated with oxygen transport. The Nb2O5crystal structure has a capacity to trap molecular oxygen, which evolves during the decomposition of Ag2O that is present in a starting mixture. The formation of the perovskite phase involves a simultaneous reaction of three species: O2, Ag, and Nb2O5/Ta2O5. As the trapped molecular oxygen is in the immediate vicinity of the reaction site, the kinetics of the reaction is significantly accelerated. An absence of the molecular oxygen in the solid-state phase cannot be compensated for with an increase in a partial pressure of oxygen in the gas phase, that is, application of oxygen atmosphere.

One of the interests and challenges of nanoindentation is determining the shear stress at the onset of plastic yielding, which corresponds to dislocation nucleation. To extract this stress information from experimental load-displacement data, a spherical tip shape is usually assumed. However, it is well known that indenter tips have irregular shapes, especially at the small-length scales that are important for small loads. This will significantly affect the stress distribution under the indentation surfaces. In this work, an indenter tip shape is measured by atomic force microscopy. The measured indenter shape is input into a finite element analysis model for indentation simulations on 〈111〉-oriented single-crystal Al samples in the elastic regime. The resulting stresses, indentation force, and contact area are analyzed and compared to results from a fitted spherical indenter. The deviation of the assumed spherical indenter tip from the real measured indenter tip is studied.

Similar to metals, the hardness of many polymers increases with decreasing indentation depths at depth ranges from several microns down to several nanometers. While for metals such phenomena are commonly attributed to geometrically necessary dislocation densities, such an explanation cannot be applied to polymers. To provide a micromechanically motivated model for the indentation size effect in polymers, here we propose an elasto-plastic extension of the higher order elasticity model recently developed by the authors. In this model, size effects in polymers (as well as in nematic liquid crystals) are related to Frank elasticity arising from bending distortions of the polymer chains and their interactions. On the basis of this theory, we derive a simple model for indentation size effects in polymers. Unlike other models, our model includes only elastic size effects due to rotational gradients. It is shown that the proposed model can explain the experimentally observed size effects in polymers. Together with the existing experimental data mentioned here, new experimental data for silicon rubber are also presented and discussed.

The surface properties of some freshly cleaved, or polished, quaternary tellurite glasses (TeO2-ZnO-Na2O-Yb2O3and TeO2-ZnO-Na2O-GeO2) and a proposed ternary fluorotellurite core/clad optical fiber pair (TeO2-N a2O-ZnF2) were investigated by means of x-ray photoelectron spectroscopy and chemical durability. Semiquantitative chemical analysis of the x-ray photoelectron spectroscopy spectra of cleaved tungsten-tellurite and fluorotellurite glasses showed good agreement with the batched at.% values when taking into account the effects of processing (e.g., melt fluorine volatilization), and the samples seemed to exhibit negligible hydrolysis. However, spectra of polished surfaces did not yield useful data because of masking of the glass “signal” from organic contamination at the sample surface. The chemical durability of these glasses were studied; specifically, the glass resistance to the attack and the etchability of various acids (aqueous HF, H2SO4, and HCl), alkali (aqueous NaOH), and water at 15, 21, and 60 °C were obtained by simple mass loss experiments and optical microscopy. Based on the appearance of the glass surfaces after immersion in these solutions, aqueous HF was found to be the most promising etchant, however, infrared spectra showed that significant OH was introduced into the glass. Attack of the fluorotellurite glasses was found to proceed at a higher rate in water at 60 °C compared with room temperature, and at both temperatures was shown to be diffusion controlled, with an Arrhenian activation energy estimated as 57 kJ mol−1.

The dynamic shear deformation process and the related stacking fault transitions in TiAl have been systematically investigated using both the molecular dynamics and ab initio methods. The details of the dislocation initiation and microstructural evolution are presented, and the concomitant potential energy variation and the radial distribution functions have been analyzed. The results show, interestingly, that some deformation-induced hexagonal close-packed (hcp) structures are metastable, and that a higher velocity field promotes more hcp segments. The phenomena are interpreted based on ab initio calculations of the detailed energy variation at the different fault transition stages, i.e., superlattice intrinsic stacking fault (SISF) → TWIN, SISF → hcp, and hcp → TWIN. The intrinsic factor that governs the deformation process is discussed. The results promote new understanding of the stress-induced interfaces and dislocation behaviors in experimental observations.

The response of a mononuclear, heteroleptic titanium alkoxide [(OPy)2Ti(4MP)2, where OPy = pyridinecarbinol; NC5H4(CH2O) and 4MP = 4-mercaptophenol; OC6H4(SH)] to ultraviolet (UV) irradiation in dilute solution and in solid-state samples has been measured. Vibrational spectroscopy [Fourier transform infrared (FTIR) absorption and Raman scattering] was used to monitor changes in molecular structure upon exposure to 337.1- and 365-nm light. Assignment of spectral features to vibrational modes of the molecule was aided by a normal-mode analysis of the energy-minimized molecular structure within a density-functional theory framework. Photoinduced decreases in peak areas were observed in both FTIR spectra of the precursor solutions and Raman data collected from solution-cast films of the precursor material. These changes were associated with vibrational modes localized at the 4MP ligands. Conversely, no significant modification of vibrational structure associated with the OPy moiety was observed under the excitation conditions examined. In a related study, thin films of the precursor were cast, sampled, and irradiated with UV light in scintillation vials under hydrated air (40% relative humidity) and dry Ar to evaluate the influence of local atmospheric composition on the photoresponse. An increase in the magnitude of photoinduced vibrational changes was observed in the moist-air environment, again associated primarily with the 4MP ligand. The results support an interpretation of these structural changes in terms of a preferential enhancement of hydrolysis at the 4MP site under these conditions. These findings are discussed in the context of an optically driven molecular assembly strategy based on the photoinitiation of intermolecular bonding at selected sites about the metal center.

As a modification to the insoluble and herringbone-structured pentacene, bis(triisopropylsilylethynyl) (TIPS) pentacene has two bulky side groups, leading to good solubility in common organic solvents and regular π–π stacking arrangements in the crystalline state. Solution processing of TIPS–pentacene thin films was investigated as a function of various process parameters in this work. Electron diffraction results suggested that TIPS–pentacene molecules tended to align with the acene unit edge on to the substrate, touching down with their bulky side groups. In a TIPS–pentacene polycrystalline film, the long axis of individual crystallite is [2 1 0], while the shorter axis is [1 ¯20]. High-resolution electron microscopy was used to study the local crystal structure and characteristic defects of TIPS–pentacene thin films. Due to the nonaromatic side groups, TIPS–pentacene was found to be significantly more sensitive to the electron beam (critical dose Jc= 0.05 C/cm2at 300 kV) than pentacene itself (Jc= 0.2 C/cm2at 100 kV).

Bulk metallic glasses (BMGs) with critical diameters of 2.5–3 mm were synthesized in the (Cu0.6Zr0.3Ti0.1)100−x−yNiyNbxsystem by copper-mold casting. These alloys exhibit a large supercooled liquid region (ΔTx) of 40–60 K and a high reduced glass transition temperature (Tg/Tl) of 0.60–0.61, indicating high glass-forming ability and high thermal stability of the supercooled liquid. The corrosion rates in 1 N HCl and 3 mass% NaCl solutions significantly decrease by simultaneous alloying with Ni and Nb elements. The addition is also effective in raising the pitting potential in chloride solutions. The addition of Ni and Nb is favorable for the alloys in forming Zr-, Ti-, and Nb-enriched highly protective surface films in HCl and NaCl solutions.

A thin nanocrystalline Pt interfacial layer (IL) was observed near the SrBi2Ta2O9(SBT)–Pt interface after crystallization treatment in a SBT–Pt–Ti ferroelectric capacitor. Apart from its Pt content, this IL also incorporated large numbers of Ti and O atoms, which arose from the Ti adhesion layer and the SBT film, respectively. These atoms reacted to form TiOx, which resulted in a volume expansion during the annealing process. This phenomenon led to a putative shear stress being exerted on the Pt layer. Under such stress and thermal conditions, we speculate that the nanocrystalline Pt IL developed from the Pt bottom electrode.

The kinetics of second phase formation during the thermal annealing of crystalline and amorphous LiNbO3(LN) thin films was investigated. When c-axis-oriented LN texture film was annealed at temperatures higher than 700 °C, Li2O desorbed from the surface and grain boundaries, which induced epitaxial precipitation of the LiNb3O8phase on the LN (0001) plane. While the LiNb3O8volume exhibited saturation behavior against annealing time, oxygen atoms continued to diffuse out from the inner part of the film. Arrhenius plots of the rate of LiNb3O8formation and oxygen loss were scaled with common activation energy of 30.5 kcal/mol. In terms of phase formation from amorphous LN, annealing at 700 °C in a vacuum induced rapid crystallization into mixtures of LN and LiNb3O8, the volume ratio of which can be explained by the phase separation model. Annealing in an O2atmosphere, however, produced an incubation time before crystallization and a larger volume fraction of LiNb3O8after crystallization. Oxygen molecules that penetrated into the film will hinder the migration of atoms and decelerate crystallization. Vacancies produced as a result of Li2O loss will facilitate the nucleation of LN and LiNb3O8pairs while maintaining the epitaxial relation.

An all-alkoxide sol-gel route to the formation of Nd1/3La1/3Ca1/3MnO3thin films and powders has been developed. The microstructural evolution on heat treatment of the gel to yield the perovskite oxide was monitored by means of thermogravimetric analysis-differential scanning calorimetry, powder x-ray diffraction (XRD), Fourier transform infrared spectroscopy, and transmission electron microscopy (TEM)-energy dispersive spectroscopy (EDS). It was found that the amorphous gel consists of hydrated oxo-carbonate without organic residues, and on heating it decomposes in several steps, finally forming single-phase perovskite at 680 °C. Further heating results in only slight changes in the cell parameters and crystal growth. Films were prepared by spin coating, followed by heat treatment in air to a temperature of 800 °C, and studied by scanning electron microscopy, TEM-EDS, and XRD. Films on Al2O3were more porous, while films on Pt–TiO2–SiO2–Si were rather dense and consisted of areas with different crystal orientations.

Iron-molybdenum powders ground in a planetary ball mill under different operating conditions were studied by x-ray diffraction line profile analysis using a recently developed whole powder pattern modeling approach. The evolution of the microstructure, expressed in terms of size distribution of coherent scattering domains, average dislocation density, and edge/screw character, shows the importance of the main process parameters: the ratio between jar and main disk rotation speeds, and ball milling time. A characteristic three-stage process is observed, with work hardening followed by particle flattening/bending before nanocrystalline grains form by a fragmentation process triggered by localized deformation. The relationship between lattice defect density and domain size suggests a progressive transition between statistically stored to geometrically necessary dislocations, with the latter mostly present as excess dislocations at the nanodomain boundary.

We present a simple method for preparing nanometer-sized, Ti-based amorphous powders from the Y28Ti28Al24Co20and Y36Ti20Al24Co20two-phase amorphous alloys. The initial microstructure of these rapidly quenched alloys is composed of Ti-based, amorphous, spherical, nanometer-sized particles embedded in a Y-based amorphous matrix, with particle size dependent on the alloy composition. The Ti-based powders were extracted from the two-phase amorphous alloys through selective dissolution of the Y-rich matrix in a 0.1 M HNO3solution. The powders of size ranging between 20 and 200 nm have smooth and spherical morphology, and exhibit different magnetic behavior than the bulk alloy of identical composition.