The crystallization behavior of melt-spun ribbons and bulk samples of the Cu36Zr48Al8Ag8 glassy alloy on heating is presented here. The crystallization kinetics and structural changes in the Cu36Zr48Al8Ag8 glassy alloy were studied using x-ray diffraction, transmission electron microscopy, differential scanning, and isothermal calorimetry methods. A clear comparison is made of the differences in the crystallization kinetics of the melt-spun ribbons and the copper-mold-cast bulk rod samples. It was suggested that the kinetics of crystallization in the rod sample, at any given temperature, are somewhat different than in the ribbon samples, probably because of size and free volume effects. Differences in the crystallization behavior of this alloy with other Cu-Zr-Al-Ag alloys have also been discussed.

Well-ordered nanoporous anodic aluminum oxide (AAO) templates have been prepared on aluminum substrates by a two-step anodization process. A voltage-controlled branching method was successfully used to thin the barrier layer of the AAO template. The nanostructures of the pores, the branched subpores, and the barrier layer in the AAO template were studied in association with the anodization process and barrier layer thinning methods. Results demonstrate the voltage-controlled branching method is a facile and effective way to thin the barrier layer. Uniform silver nanowires can be easily fabricated using alternating current (ac) electrodeposition into the pores of AAO after redressing the barrier layer.

We demonstrate here in situ synthesis of bulk yield W18O49@carbon coaxial nanocables based on an easily controlled chemical vapor deposition process at relatively low temperature (760 °C) using metallic tungsten powder and ethylene (C2H4) as the raw materials. Transmission electron microscope (TEM), energy dispersive x-ray (EDX), and x-ray diffraction (XRD) analyses indicate that the resultant nanostructures are composed of single-crystalline W18O49 nanowires, coaxially covered with amorphous carbon walls. A vapor–solid (VS) mechanism is proposed to interpret the formation of the nanocables. The effect of carbon sources on the nanocable growth was investigated. The results revealed that the introduction of carbon species not only causes the production of W18O49@C nanocable structures, but also obviously modulates growth behaviors and core/shell diameter ratio of the nanocables. The obtained nanocables may find great applications in catalyst systems and optical and electronic nanodevices because of their enhanced surface properties, as well as in high chemical stability.

The coherent fine lamellae consisting of the 2H-Mg and the 14H-type long period stacking ordered (LPSO) structure within α′-Mg matrix have been first observed in an as-cast Mg96.32Gd2.5Zn1Zr0.18 alloy. During subsequent solid solution heat treatment at 698–813 K, in addition to the lamellae within matrix, a novel lamellar X phase (Mg–8.37±1.0Zn–11.32±1.0Gd, at.%) with the 14H-type LPSO structure was transformed from the dendritical β phase, and a corresponding time–temperature–transformation (TTT) diagram was established. The 14H-type LPSO structure existing in Mg–Gd–Zn–Zr alloys derives from two variant means: the formation of LPSO structure within α′-Mg matrix and the transformation of the dendritical β phase to a lamellar X phase with the LPSO structure. The alloy solid solution treated at 773 K for 35 h exhibits higher tensile strength and better elongation than the nonheated alloy because of the lamellar X phase with the 14H-type LPSO structure and the 14H-type LPSO structure within matrix.

GaN and its alloys with InN and AlN are materials systems that have enabled the revolution in solid-state lighting and high-power/high-frequency electronics. GaN-based materials naturally form in a hexagonal wurtzite structure and are naturally grown in a (0001) c-axis orientation. Because the wurtzite structure is polar, GaN-based heterostructures have large internal electric fields due to discontinuities in spontaneous and piezoelectric polarization. For optoelectronic devices, such as light-emitting diodes and laser diodes, the internal electric field is generally deleterious as it causes a spatial separation of electron and hole wave functions in the quantum wells, which, in turn, likely decreases efficiency. Growth of GaN-based heterostructures in alternative orientations, which have reduced (semipolar orientations) or no polarization (nonpolar) in the growth direction, has been a major area of research in recent years. This issue highlights many of the key developments in nonpolar and semipolar nitride materials and devices.

The grain size of magnesium solid-solution alloys with lithium, indium, and/or zinc has been determined. Lithium, indium, and zinc additions decreased the grain size, D, of magnesium solid-solution alloys cast in a copper mold. The most effective grain refinement was obtained by zinc. In binary Mg–Zn alloys, grain size is related to the growth restriction factor, Q as D = 94 + 312/Q. In Mg–Li and Mg–In binary alloys, grain size versus growth relationships described as D = a + b/Q indicated that these alloys have lower numbers of nucleants but with higher potency than the Mg–Zn binary system. For Mg–Li and especially Mg–In, grain size could be related to growth restriction as D = 383Q−n with higher R2. Ternary and quaternary alloys based on Mg–Zn with Li and/or In additions also follow the D = a + b/Q relationship with the parameters indicating a larger number of lower potency nucleants than the Mg–Zn binary alloys. Electron probe microanalysis showed that Mg–Zn alloys exhibit pronounced and persistent grain-boundary enrichment of Zn, pointing toward Scheil solidification.

Hybrid zeolite-polyamide thin film nanocomposite (TFN) reverse osmosis membranes were synthesized by incorporating Linde type A (LTA)-type zeolite molecular sieve nanocrystals in the interfacial polymerization reaction used to form polyamide thin films. Nanocrystals were prepared with two different mobile cations (Na+ and Ag+) exchanged within the LTA crystal matrix. Incorporation of molecular sieve nanocrystals into polyamide thin films during interfacial polymerization was verified by infrared spectroscopy. Both TFN membranes exhibited higher water permeability, while maintaining similar salt rejection to pure polyamide thin film composite membranes. Nanocomposite thin films containing LTA nanocrystals in the silver form (AgA) produced a greater increase in water permeability than those in the sodium form (NaA). Furthermore, AgA-TFN membranes exhibited more hydrophilic and smooth interfaces, which appeared to inhibit adhesion of bacteria cells onto the membranes. The AgA nanocrystals exhibited significant bactericidal activity; however, when encapsulated within polyamide thin films the antimicrobial activity was significantly reduced.

The oxidation resistances of ZrB2 containing SiC, TaB2, and TaSi2 additions of various concentrations were studied using isothermal thermogravimetry at 1200, 1400, and 1500 °C, and specimens were further characterized using x-ray diffraction and electron microscopy. Increasing SiC concentration resulted in thinner glassy surface layers as well as thinner ZrO2-rich underlayers deficient in silica. This silica deficiency was argued to occur by a wicking process of interior-formed borosilicate liquid to the initially-formed borosilicate liquid at the surface. Small (3.32 mol%) concentrations of TaB2 additions were more effective at increasing oxidation resistance than equal additions of TaSi2. The benefit of these additives was related to the formation of a zirconium-tantalum boride solid solution during sintering, which during oxidation, fragmented into fine particles of ZrO2 and TaC. These particles resisted wicking of their liquid/glassy borosilicate encapsulation, which increased overall oxidation resistance. With increasing TaB2 or TaSi2 concentration, oxidation resistance degraded, most egregiously with TaB2 additions. In these cases, zirconia dendrites appeared to grow through the glassy layers, providing conduits for oxygen migration.

The microstructure, lattice parameters, electrical conductivity, thermal expansion, and mechanical properties of (La0.8Ca0.2)(Cr0.9–xCo0.1Nix)O3–δ (x = 0.03, 0.06, 0.09, 0.12) were systematically investigated in this work. Nickel doping of (La0.8Ca0.2)(Cr0.9Co0.1)O3–δ is an effective way of increasing the thermal expansion coefficient (TEC) and stabilizing the high-temperature phase transformation from rhombohedral to tetragonal. As the nickel-doped content increases, the TEC increases parabolically by TEC (x) (ppm/°C) = 10.575 + 63.3x−240x2 (x = 0.03−0.12). The electrical conductivity of (La0.8Ca0.2)(Cr0.9–xCo0.1Nix)O3–δ specimens increases systematically with increasing nickel substitution in the range of 0.03 ≤ x ≤ 0.09 and reaches a maximum for the composition of (La0.8Ca0.2)(Cr0.81Co0.1Ni0.09)O3–δ (σ850 °C ∼60.36 S/cm). There is a slight increase in the fracture toughness with increasing nickel doping content, and the fracture toughness is strongly affected by the grain size. It seems that there is an increase in the fracture toughness with decreasing grain size. However, the microhardness does not significantly depend on the grain size in this study. The (La0.8Ca0.2)(Cr0.81Co0.1Ni0.09)O3–δ specimen shows high electrical conductivity, a moderate thermal expansion coefficient, and nearly linear thermal expansion behavior from room temperature to 800 °C. It will be suitable for interconnect materials for intermediate temperature solid oxide fuel cells (IT-SOFCs).

A double-angle indenter model is proposed to determine the representative strain in the indentation process, and a new method is then developed aiming at the extraction of the yield strength and strain-hardening exponent from the surface layer of metals, because surface properties, especially in a small region, may differ from bulk ones and are sometimes closer to service properties such as fatigue strength, wear, and corrosion resistance. First, the isotropic metal was analyzed, the elastic modulus of which was fixed at 128 GPa, the yield strength was 50 to 200 MPa, and the strain-hardening exponent was 0.1 to 0.5. By introducing the yield strain to substitute the yield strength in the calculation, it was proved that the model can cover the majority of metals because the introduced weight parameter λ is independent of the yield strength and the elastic modulus, although it depends on the strain-hardening exponent to some extent. For the determination of yield strain εY (or yield strength Y), the precision is better for low C/E and low n, whereas for the determination of strain-hardening exponent n, the precision is better for high C/E and low εY. By using the double-angle indenter, the material constitutive relationship at the surface can be evaluated from just one indentation without any other measurements.

To achieve 520–532 nm green laser diodes (LDs), nonpolar and semipolar nitrides have attracted much attention because their usage leads to the elimination of the quantum-confined Stark effect and higher optical gains in this wavelength region. Since the breakthrough in the homoepitaxial growth technology for them, many nonpolar m -plane devices such as mW-class blue light-emitting diodes, violet 405 nm LDs, blue 460 nm LDs, and blue-green LDs beyond 490 nm have been announced. Advantages such as small blueshift and high slope efficiency (high output power to injected current ratio) have been confirmed for the first time in m -plane LDs beyond the blue region. On the other hand, the semipolar plane is also a candidate for green LDs. The pulsed operation of semipolar (1011) and (1122) violet LDs and lasing for a (1122) LD at 514 nm by optical pumping also have been reported. Such rapid progress in this research field will be reviewed.

The deformation behavior and indentation size effect (ISE) in amorphous and crystallized Pd40Cu30Ni10P20 alloy were comparatively studied through instrumented nanoindentation. It was found that the two alloys showed different deformation behaviors, the amorphous alloy exhibited conspicuous pop-in events in the load-depth (P-h) curve, while the crystallized alloy showed a relatively smooth P-h curve. In addition, the indentation hardness was observed to decrease with increasing penetration depth in the two alloys, exhibiting a significant ISE. However, the crystallized alloy displayed a sharper reduction of hardness with indentation depth as compared to the amorphous alloy, indicating a more significant indentation size effect in the crystalline alloy. The structure difference and friction factor associated with the surface residual stress are taken into account to interpret the difference in the deformation behavior and indentation size effect of the two alloys.

Monodisperse spherical Y2O2S:Yb,Ho nanocrystals with particle size about 50 nm were prepared by a modified homogeneous precipitation method combined with low-temperature sulfurization process. The Y2O2S:Yb,Ho nanocrystals exhibit an intense green emission assigned to the Ho3+ ions 5F4, 5S2 → 4I15/2 transition under 980 nm infrared pump. The upconversion luminescence brightness of Y2O2S:Yb,Ho is 526 Cd/m2 under 4.63 W/cm2 pump density, indicating that the as-prepared Y2O2S:Yb,Ho nanocrystals can meet the requirement of in vivo imaging. The formation mechanism of monodisperse spherical oxysulfide nanoparticles is also discussed.

This article reviews the development of nonpolar and semipolar InGaN/GaN light-emitting diodes (LEDs), emphasizing structures on freestanding bulk GaN. A brief history of LED development on each orientation is provided, followed by a discussion of the most relevant and recent results. The context is related to several current LED issues, such as the realization of high-efficiency white solid-state lighting, potential solutions to the “green gap,” and applications for polarized emitters. The section on nonpolar LEDs highlights high-power violet and blue emitters and considers the effects of indium incorporation and substrate miscut. The section on semipolar GaN reviews the development of LEDs in the violet, blue, green, and yellow regions and highlights the potential of InGaN/GaN LEDs as an alternative technology to AlInGaP for yellow emitters. A brief review of polarization anisotropy also is included for each orientation. Finally, a two source white light system utilizing a nonpolar blue LED and a semipolar yellow LED is presented.

Zinc-blende and wurtzite are the most common structures for binary compound semiconductors. Aluminum nitrides (AIN), one of the most promising materials for deep ultraviolet light-emitting diodes, have a wurtzite structure as an equilibrium phase due to its strong ionicity. Silicon carbide (SiC) is widely used as a substrate for heteroepitaxial growth of AlN, since SiC has a hexagonal structure whose lattice constant is close to that of AIN. Different from other compound semiconductors, SiC can have many different crystalline structures, called polytypism. Among various polytypes of SiC, large-size high-quality wafers are available for 4H and 6H structures. When AlN is grown on a 4H- or 6H-SiC basal plane (0001), normal, wurtzite-structured AIN is obtained. On the other hand, when AlN is grown on a nonbasal SiC plane, such as nonpolar (1100) or (1120), what is expected? If ideal growth is realized, AIN will follow the crystalline structure of SiC (i.e., the polytype of the SiC substrate will be replicated to the AIN epitaxial layer). Nonpolar nitride growth has attracted much attention to eliminate undesirable internal electric fields due to the polarization in nitride heterostructures. In addition, nonpolar nitride growth on SiC also allows an opportunity to obtain nitrides with new crystalline structures. In this article, the polytype replication growth of AIN on nonpolar SiC substrates is reviewed.