CO-gas-sensing response of individual metal–oxide–metal (MOM) heterojunction nanowires (∼250 nm diameter) in the Au–NiO–Au system, where a nanoscale segment of NiO oxide (∼250 nm long) is sandwiched axially between Au nanowires, and between individual all-oxide NiO nanowires (∼250 nm diameter, ∼5 μm long), has been measured at 150 °C. While the all-oxide nanowires are highly resistive and show no measurable response, the MOM nanowires show ∼25% decrease in current with the introduction of 800 ppm CO. The response is reversible, but it is slow due to the low temperature used. MOM nanowires, by virtue of the nanoscale-dimension, low-resistance oxide segment and the high-quality “end-on” metal–oxide contact, are an attractive class of nanowire gas-sensing elements for potential use in multifunctional “bottom up” nanoelectronics.

A new organic–inorganic hybrid synthesized through a sol-gel process starting from alkoxysilane and chitosan is reported. Functionalization of the hybrid was effected through in situ hydrolysis–condensation reaction of methyltrimethoxysilane (MTMS) and vinyltrimethoxysilane (VTMS) in the reaction medium. The process yields highly transparent and hydrophobic silica–chitosan hybrids. The hybrid gel was investigated with respect to chemical modification, thermal degradation, hydrophobicity, and transparency under the ultraviolet-visible region. The extent of hydrophobicity had been tailored by varying the precursor ratio. SiO2–chitosan–MTMS hybrids showed a higher thermal stability than SiO2–chitosan–VTMS (SCV) hybrids with respect to hydrophobicity. Condensation of silsesquioxanes generated from the hydrolysis of MTMS and VTMS over the silica-chitosan particles impart hydrophobicity to the hybrid. The coatings of functionalized SiO2–chitosan precursor sol on glass substrates showed nearly 100% optical transmittance in the visible region. The present hybrid material may find application in optics and other industries.

A novel vapor-transport-assisted wet chemistry process was developed to fabricate oxide nanodot arrays from soft polymer templates. The feasibility and wide applicability of the proposed process was demonstrated with creation of high-density oxide nanodot arrays of TiO2, ZnO, and Co3O4. The present process not only avoids the over-growth problem inevitable in wet chemistry processes but also enables formation of oxide nanodots at low temperatures. The process can be readily extended to other compound systems in which the products can be formed through reactions of two reactants, one in liquid phase and the other in vapor phase.

Phases that are in equilibrium with BaR2CuO6+x (R=lanthanides and Y), such as the “green-phase” and “brown-phase” structural variants of BaR2CuO5 in bulk samples, are attractive choices for flux-pinning for coated conductor applications because of the guaranteed chemical stability. In films, high-temperature x-ray diffraction studies of Ba2RCu3O6+x superconductor deposited on SrTiO3 substrate using the trifluoroacetate solution method demonstrate that while BaNd2CuO5 (“brown-phase” structure) develops at 735 °C and 100 Pa pO2, neither BaGd2CuO5 nor Ba(Nd1/3Eu1/3Gd1/3)2CuO5 (both green-phase structure) form at these conditions. As a result, Ba2(Nd1/3Eu1/3Gd1/3)Cu3O6+x in thin films is in equilibrium with the brown-phase, and Ba2GdCu3O6+x is in equilibrium with Gd2O3 in the Ba–Gd–Cu–O system, in contrast to the bulk systems. Different phase relationships in the vicinity of the Ba2RCu3O6+x phase imply different phases are available for flux-pinning applications. These differences will need to be considered carefully in designing optimized superconducting coated conductors.

A novel ZnO seedless chemical approach for density-controlled growth of ZnO nanowire (NW) arrays has been developed. The density of ZnO NWs is controlled by changing the precursor concentration. Effects of both growth temperature and growth time are also investigated. By this novel synthesis technique, ZnO NW arrays can grow on any substrate (polymer, glass, semiconductor, metal, and more) as long as the surface is smooth. This technique represents a new, low-cost, time-efficient, and scalable method for fabricating ZnO NW arrays for applications in field emission, vertical field effect transistor arrays, nanogenerators, and nanopiezotronics.

Upconversion luminescence (UPL) characteristics and effects of Li+ ion on the UPL of ZnWO4:Yb,Er polycrystalline phosphors were investigated. It was shown that introduction of Li+ ions could reduce the calcination temperature by about 200 °C and increase the crystallinity of ZnWO4:Yb,Er by a liquid-phase sintering process via formation of Li2WO4 and other intermediates. UPL efficiency is remarkably promoted by Li+ ions. Moreover, the UPL spectrum of Li+-doped ZnWO4:Yb,Er presents a red shift, and the strongest peak position shifts from 553 to 559 nm. These can be attributed to a shift in the 4f level barycenter to lower energy, which results from lowering of the symmetry of the crystal field around Er3+.

Hybrid thick films were deposited on Surlyn, a copolymer of poly(ethylene- co-methacrylic acid) and a common adhesion film for metal surfaces. Hybrid organic–inorganic materials were prepared by a sol-gel process. Methyltriethoxysilane (MTES) with tetraethoxysilane (TEOS), phenyltriethoxysilane (PhTES) with TEOS, and methyltrimethoxysilane (MTMS) with tetramethoxysilane (TMOS) were investigated. The inorganic component was selected to form the network for the film, while the organic component was selected to repel water and fill porosity. The films were deposited on Surlyn and on glass slides. The properties of the films were investigated using attenuated total reflection Fourier transform infrared (FTIR) and Raman spectroscopy. Contact-angle measurements indicated that the contact angle increased from ∼76.5° for Surlyn alone to ∼89.6° for Surlyn coated with MTES.

In this paper, we systematically demonstrate the corrosion behavior and surface characteristics of a newly developed Cu36Zr48Ag8Al8 bulk metallic glass (BMG). The Cu36Zr48Ag8Al8 BMG exhibits excellent corrosion resistance in acidic and alkaline solutions without Cl− ions. The alloy is spontaneously passivated with a markedly low current density in 1 N H2SO4 solution. The formation of the bilayered passive film of the present alloy immersed in 1 N H2SO4 solution, which is composed mostly of Zr4+ cations in the exterior part and Zr4+- and Al3+-enriched cations in the inner part, could be responsible for the high corrosion resistance.

This work reports on thermal and electrical conductivities and interface resistances for transport along aligned multiwalled carbon nanotubes (CNT) films grown on a nickel superalloy (Inconel) substrate. The measured specific thermal resistance of the combined Inconel–CNT and indium–CNT interfaces is of the same order as reported for CNT and silicon or SiO2 interfaces but much higher than theoretical predictions considering perfect contact between the tubes and substrate. Imperfect mechanical contact with the substrate and a large contribution caused by indium–CNT interface are thought to be mainly responsible for the high interface resistances and the low effective values of thermal and electrical conductivities. However, reported results represent an incentive for further research on CNT synthesis on metallic substrates for thermal management applications and pave the way for much easier integration of carbon nanotubes in electronic applications.

We previously proposed a method for estimating Young’s modulus from instrumented nanoindentation data based on a model assuming that the indenter had a spherical-capped Berkovich geometry to take account of the bluntness effect. The method is now further improved by releasing the constraint on the tip shape, allowing it to have a much broader arbitrariness to range from a conical-tipped shape to a flat-ended shape, whereas the spherical-capped shape is just a special case in between. This method requires two parameters to specify a tip geometry, namely, a volume bluntness ratio Vr and a height bluntness ratio hr. A set of functional relationships correlating nominal hardness/reduced elastic modulus ratio (Hn/Er) and elastic work/total work ratio (We/W) were established based on dimensional analysis and finite element simulations, with each relationship specified by a set of Vr and hr. Young’s modulus of an indented material can be estimated from these relationships. The method was shown to be valid when applied to S45C carbon steel and 6061 aluminum alloy.

Anodized films of titanium were prepared under different controlled conditions in a water-based electrolyte containing fluorine ions, using either a constant potential or a potential gradually rising to 20 V. The films were then examined using transmission electron microscopy at different stages of growth, in particular, the very early stages of growth (30 s, 200 s, and 10 min) and when the ordered nano-tubular structure was finally established (2–4 h). The use of ramped voltage during the early stages of anodization allowed a well-interconnected porous network to develop and maintained active oxidation throughout anodization. The film, as formed, consisted mainly of amorphous oxide/hydroxides of titanium with small regions of nano-sized crystals. These were found more often in the denser regions of the amorphous network, particularly the arms of the coral-like structure that formed. As the anodized film grew in thickness, the pores tended to become aligned, leading to a surface layer of nanotubes on the electrode material. Electron optical characterization revealed that the nanotubes consist of a stack of rings where the passage of the current had been optimized.

Electrical conductivities of various mullite/zirconia composites, as well as monolithic mullite and zirconia, were measured using AC impedance spectroscopy from 100 Hz to 10 MHz at temperatures ranging from 150 to 1300 °C. The impedance spectra of monolithic zirconia and mullite/zirconia composites showed two semicircles because of the contributions from grains and grain boundaries, while those of monolithic mullite had one semicircle due to the predominant contribution from grains. This indicates that the conductivities of the mullite/zirconia composites increased with zirconia content. The activation energies of electrical conduction in mullite and zirconia were about 65 and 79 kJ/mol, respectively, and those of mullite/zirconia composites were between 65 and 79 kJ/mol. While the conductivities of various composites at 1 MHz were fitted by Lichtenecker’s rule, the general mixing equation could be applied to the conductivities measured at 1 kHz.

In a compression test for a Zr-based bulk metallic glass, a dominant shear band was preserved before fracture by a cylindrical stopper. A heat-affected zone (HAZ) ∼10 μm thick together with shear band was discovered in the center of the deformed sample by preferential ion milling. By using a low aspect ratio sample for compression, diverse micron-scaled HAZs among multiple shear bands were also revealed. Based on above experimental results and the isothermal source model, it was found that the thickness of shear band and its HAZ increased continuously with the progression of shear deformation.

Anomalous eutectics in the solidification structure of undercooled Ni–18.7 at.% Sn eutectic alloy were examined by optical metallography and electron backscattered diffraction. It was revealed that α–Ni particulates are, in principle, randomly distributed in the anomalous eutectics in the undercooling range investigated. Another eutectic phase, β–Ni3Sn, is well orientated at low undercoolings but gradually becomes inconsistent in orientation as undercooling increases, accompanied by an increasing number of grain boundaries in it. As the solidification structure changes from a mixture of anomalous eutectics plus lamellar eutectics to full anomalous eutectics beyond a critical undercooling of 130 K, however, misorientation in the β–Ni3Sn phase disappears completely from the measurement area. Partial remelting of the primary solid was proposed to be the origin of the anomalous eutectic formation, and quantitative analyses were performed.

Three-point bend test coupled with transmission electron microscopy (TEM) analysis was carried out on individual tungsten oxide nanowires (NWs) before and after annealing. Three-point bend test monitors the change in the Young’s modulus of the NW after annealing, while TEM provides nanostructural detail changes on the same NW. In this way, insight into the correlation between the mechanical properties of a NW and its nanostructure details can be obtained. Annealing increased the diameter of the NWs by forming a uniform amorphous/polycrystalline outer coating. The coating results in a decrease in Young’s moduli for thicker NWs. On the other hand, annealing led to increased Young’s moduli of thinner NWs, which is attributed to the improved crystallinity in these NWs after annealing. This study points to a more refined strategy for more in-depth understanding of the relationship between the nanostructures and elastic mechanical properties of NWs.

Herein we report on the synthesis and characterization of Cr2GeC, a member of the so-called Mn+1AXn (MAX) phase family of layered machinable carbides and nitrides. Polycrystalline samples were synthesized by hot pressing pure Cr, Ge, and C powders at 1350 °C at ∼45 MPa for 6 h. No peaks other than those associated with Cr2GeC and Cr2O3, in the form of eskolaite, were observed in the x-ray diffraction spectra. The samples were readily machinable and fully dense. The steady-state Vickers hardness was 2.5 ± 0.1 GPa. The Young’s moduli measured in compression and by ultrasound were 200 ± 10 and 245 ± 3 GPa, respectively; the shear modulus and Poisson’s ratio deduced from the ultrasound results were 80 GPa and 0.29, respectively. The ultimate compressive strength for a ∼20 μm grain size sample was 770 ± 30 MPa. Samples compressively loaded from 300 to ∼570 MPa exhibited nonlinear, fully reversible, reproducible, closed hysteretic loops that dissipated ∼20% of the mechanical energy, a characteristic of the MAX phases, in particular, and kinking nonlinear elastic solids, in general. The energy dissipated is presumably due to the formation and annihilation of incipient kink bands. The critical resolved shear stress of the basal plane dislocations—estimated from our microscale model—is ∼22 MPa. The incipient kink band and reversible dislocation densities, at the maximum stress of 568 MPa, are estimated to be 1.2 × 10−2 μm−3 and 1.0 × 1010 cm−2, respectively.

The amorphous-to-crystalline transformation behavior of Fe48Cr15Mo14Y2C15B6 bulk metallic glasses was first investigated by high-temperature differential scanning calorimetry. Three events were detected with onset temperatures at 922, 975, and 1036 K, respectively. In situ synchrotron radiation x-ray diffraction patterns were collected during continuous heating and analyzed with the Rietveld approach. To describe simultaneously the amorphous fraction and crystallization products as a function of temperature, a paracrystalline structure-factor model was developed. It was included for quantitative evaluation of the amorphous phase, together with the structure factor of Cr23C6- and Fe3Mo3C-type phases observed during crystallization. Volume fractions of phases as well as lattice parameters, average lattice disorder, and crystallite size of the crystallized phases have been followed as a function of temperature. In this way, the structure evolution and thermal events have been closely inspected and accounted for by a crystallization mechanism.

Nanostructured carbon materials, including carbon nanotubes, nanofibers, and nanowalls, exhibit a wide range of interesting properties dictated by the many different bonding configurations. Many of these materials can possess superhydrophobic behavior when water drops are placed on their surfaces: these drops have high contact angles and can roll freely on the surfaces, which is desirable for self-cleaning. In this work, we prepared porous carbon films using a microwave plasma enhanced chemical vapor deposition technique. These films showed superhydrophobicity with contact angle of 150°, which was explained by the synergetic effect of the highly rough surface combined with the hydrogen terminated edges of graphene sheets. However, the condensed water drops can behave differently: the drops did not roll readily. This behavior mimicked that of water on lotus leaves and further demonstrated that the reported superhydrophobic behavior is a function of how the water gets on to the surfaces.

Results on mechanical alloying of binary and ternary Mg–Ti-based mixtures are reported. Using fine-powdered reactants and a process-control-agent, a mixture of two face-centered cubic compounds is obtained. Using a coarse Mg precursor without addition of a milling agent results in a hexagonal-solid solution of Ti in Mg due to a lower oxygen content in the Mg starting material. Upon introduction of Ni or Al as a third element, the amount of dissolved Ti decreases to form a nanocrystalline secondary phase. The electrochemical charging capacity of the hexagonal compounds is far superior to that of the cubic ones, whereas the discharge capacity is significantly increased only upon addition of Ni. The secondary TiNi phase acts as a rapid diffusion path for hydrogen, greatly improving the rate capability of the alloys. The reversible hydrogen storage capacity reaches values of up to 3.2 wt% at room temperature for (Mg0.75Ti0.25)0.90Ni0.10.

The structure and configuration of threading dislocations (TDs) in AlN films grown on (0001) sapphire by metal–organic vapor phase epitaxy (MOVPE) were characterized by high-resolution transmission electron microscopy (HRTEM). It was found that the TDs formed in the films were mainly the perfect edge dislocations with the Burgers vector of b = ⅓〈11¯20〉. The majority of the edge TDs were not randomly formed but densely arranged in lines. The arrays of the edge TDs were mainly observed on the {11¯20} and {10¯10} planes. These two planes showed different configurations of TDs. TD arrays on both of these planes constituted low-angle boundaries. We suggest that these TDs are introduced to compensate for slight misorientations between the subgrains during the film growth.