The ignition and reaction mechanisms of the thermal explosion reaction in the Ni-Ti-C system under air and Ar conditions were investigated. The reaction for the formation of TiC can be initiated at a low temperature under air. The ignition temperature under air is much lower than that under Ar. Under Ar, both the ignition and reaction mechanisms consist of dissolution, reaction, and precipitation. Under air, the ignition mechanism is confirmed to be the chemical oven mechanism, and the reaction mechanism is dissolution, reaction, and precipitation. The mechanism of gas transport plays a much more minor role in the ignition and reaction processes under air.

Atom-probe tomography (APT) is in the midst of a dynamic renaissance as a result of the development of well-engineered commercial instruments that are both robust and ergonomic and capable of collecting large data sets, hundreds of millions of atoms, in short time periods compared to their predecessor instruments. An APT setup involves a field-ion microscope coupled directly to a special time-of-flight (TOF) mass spectrometer that permits one to determine the mass-to-charge states of individual field-evaporated ions plus their x-, y-, and z-coordinates in a specimen in direct space with subnanoscale resolution. The three-dimensional (3D) data sets acquired are analyzed using increasingly sophisticated software programs that utilize high-end workstations, which permit one to handle continuously increasing large data sets. APT has the unique ability to dissect a lattice, with subnanometer-scale spatial resolution, using either voltage or laser pulses, on an atom-by-atom and atomic plane-by-plane basis and to reconstruct it in 3D with the chemical identity of each detected atom identified by TOF mass spectrometry. Employing pico- or femtosecond laser pulses using visible (green or blue light) to ultraviolet light makes the analysis of metallic, semiconducting, ceramic, and organic materials practical to different degrees of success. The utilization of dual-beam focused ion-beam microscopy for the preparation of microtip specimens from multilayer and surface films, semiconductor devices, and for producing site-specific specimens greatly extends the capabilities of APT to a wider range of scientific and engineering problems than could previously be studied for a wide range of materials: metals, semiconductors, ceramics, biominerals, and organic materials.

Zr–N films were grown on glass and Si (100) substrate by radio-frequency magnetron sputtering using a mixture of high pure nitrogen and argon as sputtering gases. The structure and properties of Zr–N compounds in the films change with N2/(N2+Ar) flow ratio (RN2). At low RN2, a ZrN alloy with the rocksalt structure (denoted as γ-ZrNx) is formed. The N concentration x and lattice constant increases with increasing RN2, and x reaches 1 when the RN2 goes up to 20%. As the RN2 exceeds 20%, the film is composed of γ-ZrN and Zr3N4 phase with Th3P4 structure (denoted as c-Zr3N4). The relative content decreases for the γ-ZrN but increases for the c-Zr3N4 with increasing RN2, and a single phase of c-Zr3N4 was deposited on glass at RN2 of 100%. The c-Zr3N4 behaves with p-type conductivity with a band gap of 2.8 eV. The lattice constant of the c-Zr3N4 was measured to be ∼0.674 nm. The mechanism of the phase transition from γ-ZrN to c-Zr3N4 with increasing RN2 was suggested.

A recent report on the “room temperature superplasticity” in the Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass [Y.H. Liu et al., Science315, 1385 (2007)] was ascribed to the distinctive micrometer-sized structural heterogeneity. To verify the microstructure in this alloy, transmission electron microscopy (TEM) and anomalous small-angle x-ray scattering experiments were conducted. The results show that no micrometer-sized or nanometer-sized structural heterogeneities can be found. The micrometer-sized dark and bright regions that were previously reported as the reason for the plasticity are artifacts caused by TEM specimen preparation, rather than the intrinsic structure feature of this alloy. This finding is important for further studying the unique properties of this alloy.

Cobalt (15 at.%) doped bismuth vanadate, Bi4(V0.85Co0.15)2O11-δ (BICOVOX0.15), is known to have high oxygen ion conduction in the medium temperature range (400–600 °C). Small grain size may be important in stabilizing the highly conductive and disordered γ-phase at lower temperature. In this article, we report for the first time the synthesis of highly porous nanoscale BICOVOX powders by a solution combustion technique. The effects of fuel-to-oxidizer ratio, and postcombustion heat treatment temperature and time on the phase content and microstructure of the powders were investigated. As-combusted powders were revealed to be a mixture of Bi2O3, BiVO4, and γ-BICOVOX phases that were converted to phase pure γ-BICOVOX during heat treatment.

An analytical solution for the Kissinger equation relating the activation energy, E, with the peak temperature of the reaction rate, Tm, has been found. It is accurate (relative error below 2%) for a large range of E/RTm values (from 15 to above 60) that cover most experimental situations. The possibilities opened by this solution are outlined by applying it to the analysis of some particular problems encountered in structural relaxation of amorphous materials and in kinetic analysis.

Nanoscale surface texturing of silicon was accomplished by oblique Ar+ ion beam irradiation. Atomic force microscope (AFM) imaging showed that nanotexturing produced an anisotropic morphology consisting of ordered nanometer-sized ripples. Surface force microscope (SFM) measurements showed that the nanotextured surface exhibited scale-dependent nanomechanical behavior during indentation loading/unloading and anisotropic sliding friction, significantly different from those of the original (untextured) surface. AFM and SFM results showed a strong dependence of the nanoindentation response and friction coefficient on the tip radius and sliding direction relative to the ripple orientation. The observed experimental trends are interpreted in terms of the applied normal load, real contact area, interfacial adhesion force, tip-ripple interaction scale, and ripple orientation.

Photonic crystals, in which the refractive index changes periodically, provide an exciting new tool for the manipulation of photons and have received keen interest from a variety of fields. This article reviews recent progress in the manipulation of photons by photonic crystals. First, the article covers spontaneous emission, a fundamental phenomenon associated with all photonic devices that emit light, which now can be successfully controlled. Light emission is suppressed in areas where the photonic crystal is complete, while strong emission occurs in the areas where there are artificial defects. Next, it is shown that a very strong confinement of photons in a small volume on the scale of cubic wavelengths becomes possible by using photonic crystals, where nanocavities with ultrahigh-Q values of more than 2 million have been successfully demonstrated. Finally, photonic crystals promise to realize unprecedented types of lasers, which can produce tailored beams on demand, while keeping stable single longitudinal and lateral modes.

We used reverse Monte Carlo (RMC) modeling to simulate the atomic structure of a Zr-based bulk metallic glass (BMG), incorporating short-range structural data from the electron diffraction total reduced density function G(r) and medium-range structural data from fluctuation electron microscopy (FEM). Including the FEM data created within the model loosely ordered planar atomic arrangements covering regions ∼1 nm in diameter without degrading the agreement with G(r). RMC refinement against only G(r) produced no agreement with FEM. Improved simulations are needed to create fully realistic BMG structures, but these results show that including FEM in RMC further constrains the structure compared with G(r) data alone and that the FEM signal in real materials is likely to arise from pseudo-planar arrangements of atoms.

We performed density-functional calculations of oxygen incorporation and diffusion in layered Ti2AlC for a range of intrinsic- and impurity-element chemical potentials. In view of the thermal equilibrium coexistence between oxygen-dissolved Ti2AlC and the oxide scale, a thermodynamic scheme is presented that allows the comparison of the relative stability of oxygen defects in different exterior environments. The calculations show that the oxygen atom favors substitution on carbon lattice sites (OC) under oxygen-lean conditions and high temperatures, whereas the occurrence of an oxygen interstitial in the aluminum atomic layer (IO-tri) becomes more preferential in an oxygen-rich atmosphere and low temperatures. Interstitial oxygen (IO-tri) diffusion via a metastable interstitial site (IO-oct) has a comparatively low migration energy. The substitutional oxygen defect (OC) diffuses by exchanging with neighboring carbon vacancy, which needs a relatively high diffusion barrier.

The thermal stability and corrosion behavior of the nanostructured layer on commercially pure zirconium, produced by surface mechanical attrition treatment (SMAT), were investigated. It is indicated that the nanograined Zr is stable at annealing temperatures up to 650 °C, above which significant grain growth occurs and the grain size shows parabolic relationship with annealing time. The activation energy for grain growth of the nanograined Zr is 59 kJ/mol at 750–850 °C, and the grain growth is dominated by grain-boundary diffusion. The as-SMATed nanograined Zr exhibits higher corrosion resistance than the 550–750 °C annealed SMATed Zr and the unSMATed coarse-grained Zr. It is indicated that the corrosion resistance of Zr tends to increase with the reduction of grain size, which is related to the dilution of segregated impurities at grain boundaries due to grain refinement and the formation of passive protection film.

The effect of porosity on the kinetics of the austenite to bainite isothermal transformation in powder metallurgy steels was characterized using a high-speed quenching dilatometer. The measurements revealed that the presence of porosity shortens the incubation time as well as the overall isothermal transformation time. An Avrami-type equation was fitted to the measured data, and the effect of porosity on the nucleation rate of bainite was quantified. In addition, the activation energy for diffusion of carbon atoms during nucleation of bainite was calculated and was found to decrease with increasing porosity.

In order to study the electronic properties of conjugated polymer nanowire junctions, we have fabricated two devices consisting of two crossed poly(3,4-ethylenedioxythiophene) (PEDOT) nanowires with platinum microleads attached to each end of each nanowire. We find that the junction resistance of the crossed nanowires is much larger than the intrinsic resistance of the individual PEDOT nanowire, and increases with decreasing temperature, which can be described by a thermal fluctuation-induced tunneling conduction model. In addition, the crossed junctions show linear current-voltage characteristics at room temperature.

Dispersed crystalline copper particles were prepared by reacting aqueous dispersions of CuCl with ferrous citrate. We report that the Fe(II) citrate complex can reduce rapidly and completely cuprous chloride to metallic copper and propose a mechanism for the reaction observed. By changing the precipitation conditions, copper particles with sizes varying from 250 nm to 2.0 µm were obtained. The method described represents a simple and versatile approach for preparing copper powders for electronic applications.

The evolution of shear bands (SBs) into cracks was observed by using a high-resolution scanning electron microscope in Zr59Cu20Al10Ni8Ti3 metallic glassy samples after a small punch test with different strain rates. As shear strain increased along a radial SB, three distinctive regions of morphologies were found (I) bonded SB, (II) microcrack plus bonded SB, and (III) full crack. In region II with moderate shear strain, some glassy “extrusions” were also observed. Once shear offset increases to a critical value, the SB becomes a full crack. For two different SBs in one specimen, the critical shear offsets maintain approximately the same value, which sheds light on the critical shear failure condition of metallic glass. The critical shear offset was also found to be sensitive to the strain rate and a higher strain rate led to less critical shear offset. It is suggested that the structure evolution and heat evolution within a shearing SB should be responsible for the previous results.