Void formation in lead-free solder joints, away from the joint interface, has been observed after solid-state aging. These voids are attached to intermetallic precipitates in the solder matrix, especially to those that are adjacent to the layered intermetallic at the joint interface. Two potential void formation mechanisms are discussed. The mechanism proposed to describe void formation is that a flux of vacancies is created due to volume contraction during solid-state reaction. The ripening process among the intermetallics also assists this process. Using the suggested mechanisms, the void size was estimated. This phenomenon differs from the classical Kirkendall void formation because it is a nonequilibrium state of void formation and stress generation.

The authors have devised a novel organic light-emitting transistor (OLET) with a PN-heteroboundary combined with hole and electron transport materials (in other words, p-type and n-type organic semiconductors) along carrier channels. In this device, a clear modulation of the current and luminance with the gate voltage was observed. A luminance of 100 cd/m2 or more has been observed at the source–source voltage of 15 V with the turn-on voltage of 10 V or less, which is lower than that of OLETs based on a single organic material. The horizontal PN-heteroboundary structure has been implemented for the first time by using the photolithographic patterning of organic semiconductor thin films. This patterning technique can be applied to the fabrication of not only the OLETs reported in this work, but also to organic integrated circuits or organic displays.

We present a new process based on the electrolysis of glass, which allows the transfer of a single-crystal silicon film while creating an in situ barrier layer free of mobile ions in the glass. This barrier layer consists only of network-forming elements (i.e., aluminum, silicon, and boron) and is free of modifiers. The barrier layer glass is unusual and cannot be synthesized via any of the known glass-forming processes. The barrier layer is thermally stable and thus allows the fabrication of displays with ultimate performance. The process consists of the hydrogen ion implantation of silicon to create a defect structure followed by bringing the glass and the silicon wafer in contact, and finally applying electrical potential to cause the electrolysis of glass.

Light-induced metastability in hydrogenated nanocrystalline silicon (nc-Si:H) single-junction solar cells was studied systematically. First, we observed no light-induced degradation when the photon energy was lower than the band gap of the amorphous phase; degradation occurred when the energy was higher than the band gap in the amorphous phase. The light-induced degradation could be annealed away at an elevated temperature. We concluded that the light-induced defect generation occurred mainly in the amorphous phase. Second, forward current injection did not degrade the nc-Si:H cell performance. However, a reverse bias during light soaking enhanced the degradation. Third, the nc-Si:H cells made with an optimized hydrogen dilution profile showed minimal degradation although these cells had a high amorphous volume fraction. This indicated that the amorphous volume fraction was not the only factor determining the degradation. Other factors also played important roles in the nc-Si:H stability.

High performance Fe-cladded MgB2 taps were prepared by the in situ powder-in-tube method utilizing very cheap stearic acid (C18H36O2) as dopants. The amount of stearic acid was varied from 0 to 30 wt%. We found that a significant enhancement of Jc, Hirr, and Hc2 in comparison with undoped samples was easily achieved. At 4.2 K, the transport Jc for the best doped tapes (10 wt%) reached 2 × 104 A/cm2 at 10 T and 3.7 × 103 A/cm2 at 14 T, respectively, an order of magnitude higher than for the pure tapes. In particular, at 20 K, the irreversibility field of the 10 wt% doped tape was around 10 T, which is comparable to the upper critical field of the commercial NbTi at 4.2 K. The results demonstrate great potential of MgB2 tapes for superconducting magnets.

P- and n-type conductivity domains in dual-doped ZnO:As+N layers grown by metal organic vapor phase epitaxy on GaN–sapphire templates were electrically microcharacterized by scanning capacitance microscopy (SCM) and scanning surface potential microscopy (SSPM) techniques with respect to their defect states. The p-type domains were found to be dominated by two acceptors with thermal activation energies of about 80 and 270 meV, as observed by transient SCM scans at different temperatures. Optically excited SSPM scans revealed defect-to-band transitions at 400, 459, and 505 nm omnipresent in both domain types as well as a shallower transition at 377 nm exclusively in the p-type regions. According to the similar energy levels, the optical transitions at 377 and 400 nm are assigned to acceptor states, whereby the 80-meV acceptor is probably responsible for the conversion from n- to p-type regions in the domains.

Phase change materials possess a unique combination of properties, which includes a pronounced property contrast between the amorphous and crystalline state, i.e., high electrical and optical contrast. In particular, the latter observation is indicative of a considerable structural difference between the amorphous and crystalline state, which furthermore is characterized by a very high vacancy concentration unknown from common semiconductors. Through the use of ab initio calculations, this work shows how the electric and optical contrast is correlated with structural differences between the crystalline and the amorphous state and how the vacancy concentration controls the optical properties. Furthermore, crystal nucleation rates and crystal growth velocities of various phase change materials have been determined by atomic force microscopy and differential thermal analysis. In particular, the observation of different recrystallization mechanisms upon laser heating of amorphous marks is explained by the relative difference of just three basic parameters among these alloys, namely, the melt-crystalline interfacial energy, the entropy of fusion, and the glass transition temperature.

The dry sliding friction coefficient μ and the wear volume loss W, in a zirconium-based bulk metallic glass (BMG) under high-frequency (50 Hz) reciprocating conditions, were investigated with the objective of assessing the influence of free volume and crystallization on the wear behavior of amorphous metals. The BMG samples were annealed either below the glass transition temperature Tg to induce structural relaxation and hence reduce the free volume that controls plasticity through shear-band formation or above Tg to crystallize the amorphous BMG prior to wear testing. Results show that the wear behavior of both the as-cast and relaxed glasses was dominated by the oxidation of the surface layers. A sharp transition in the contact electrical resistance complemented by a marked increase in μ was noted. This was attributed to the formation of a thick tribo film with high oxygen concentration and its subsequent delamination. The μ values, before as well as after the transition, in the relaxed glasses were similar to those for the as-cast alloy. However, a gradual decrease in W with annealing temperature was observed. A good correlation between W and nanohardness was noted, implying that the intrinsic hardness in the BMGs controlled the wear rate.

The recent interest in oxidation catalysis provides the focus for this article. Until recently, gold has been overlooked as a key component of both homogeneous and heterogeneous catalysts. However, the observation in the 1980s that nanocrystalline gold supported on oxides was an effective catalyst for low-temperature carbon monoxide oxidation has now captured the imagination of many researchers. At present, low-temperature carbon monoxide oxidation remains an intensely studied field, but in recent years increased emphasis has been placed on using gold catalysts for selective oxidation. For example, the oxidation of alkanes, alkenes, and alcohols have all been shown to be effective with gold-based catalysts. In addition gold–palladium bimetallic catalysts have been shown to be very effective for the direct formation of hydrogen peroxide, and this will be described in this article.

We observed the enhancement of fluorescence intensity due to the addition of GeO2 in bismuth-doped silica glass (BiSG), which has a peculiar fluorescence at 1.25 μm with a full width at half-maximum of 300 nm. Experimental results revealed that the fluorescence intensity from BiSG with 5.0 mol% GeO2 increased remarkably to be 26.3 times greater than that without GeO2 additive for the same Bi2O3 concentration (0.1 mol%). Furthermore, the enhanced sample showed almost the same intensity as BiSG without GeO2 for 1.0 mol% Bi2O3. These results demonstrate that GeO2 additive effectively promotes the generation of peculiar luminescent centers.

A controversial issue in mechanical property extractions from instrumented indentation applied load (P)–penetration depth (hs) curves concerns the possibility of finding more than one solid that essentially exhibits the same contact response. By recourse to finite element simulations of elastic-power law strain hardening solids, it was shown that for both the elasto-plastic and the fully plastic contact regimes it becomes possible to find an arbitrary number of solids whose P-hs curves are visually similar [L. Wang and S.I. Rokhlin, J. Mater. Res. 21, 995 (2006)]. Although this assertion supports prior findings [e.g., C.M. Cheng and Y.T. Cheng, J. Mater. Res. 14, 3493 (1999); K.K. Tho et al., Mater. Sci. Eng.A 390, 202 (2005); and J. Alkorta et al., J. Mater. Res.20, 432 (2005)], it apparently contradicts the work by Casals and Alcalá in which, through similar computational procedures and constitutive theory, it was shown that there can be “only” two solids with strictly the same P-hs curve [O. Casals and J. Alcalá, Acta Mater.53, 3545 (2005)]. The purpose of this comment is to reconcile the different views on the multiplicity of inferred properties that can be extracted from a single P-hs curve, as well as to address the issue of whether visually similar P-hs curves can be taken to be statistically identical both from analytical and experimental standpoints. Some considerations are also given regarding experiments performed with dual indenters.

We investigated the effect of strain rate on the plastic-flow stress of a Zr-based bulk-metallic glass in quasistatic compression. The results indicate that the plastic-flow stress is dependent on the strain rate: an increase in the strain rate leads to a decrease in the plastic-flow stress, and vice versa. However, simply loading, unloading, and reloading at a constant strain rate do not change the plastic-flow stress. This strain-rate dependence of the plastic-flow stress may be related to shear-banding operations.

Out-of-phase boundaries (OPBs) are translation boundary defects characterized by a misregistry of a fraction of a unit cell dimension in neighboring regions of a crystal. Although rarely observed in the bulk, they are common in epitaxial films of complex crystals due to the physical constraint of the underlying substrate and a low degree of structural rearrangement during growth. OPBs can strongly affect properties, but no extensive studies of them are available. The morphology, structure, and nucleation mechanisms of OPBs in epitaxial films of layered complex oxides are presented with a review of published studies and new work. Morphological trends in two families of layered oxide phases are described. The atomic structure at OPBs is presented. OPBs may be introduced into a film during growth via the primary mechanisms that occur at film nucleation (steric, nucleation layer, a-bmisfit, and inclined-cmisfit) or after growth via the secondary nucleation mechanism (crystallographic shear in response to loss of a volatile component). Mechanism descriptions are accompanied by experimental examples. Alternative methods to the direct imaging of OPBs are also presented.

We investigated the role of particle potential symmetry on self-assembly by Monte Carlo simulation with a particular view toward synthetically creating structures of prescribed form and function. First, we established a general tendency for the rotational potential symmetries of the particles to be locally preserved upon self-assembly. Specifically, we found that a dipolar particle potential, having a continuous rotational symmetry about the dipolar axis, gives rise to chain formation, while particles with multipolar potentials (e.g., square quadrupole) having discrete rotational symmetries lead to the self-assembly of “random surface” polymers preserving the rotational symmetries of the particles within these sheet structures. Surprisingly, these changes in self-assembly geometry with the particle potential symmetry are also accompanied by significant changes in the thermodynamic character and in the kinetics of the self-assembly process. Linear chain growth involves a continuous chain growth process in which the chains break and reform readily, while the growth of the two-dimensional polymers only occurs after an “initiation” or “nucleation” time that fluctuates from run to run. We show that the introduction of artificial seeds provides an effective method for controlling the structure and growth kinetics of sheet-like polymers. The significance of these distinct modes of polymerization on the functional character of self-assembly growth is illustrated by constructing an artificial centrosome structure derived from particles having continuous and discrete rotational potential symmetries.

Tension and stress-relaxation behaviors of a La62Al14Cu11.7Ag2.3Ni5Co5 bulk metallic glass (BMG) as a function of isothermal annealing time have been investigated. It is found that annealing at 373 K below the glass-transition temperature (423 K) of the BMG alloy causes an increase of special heat difference at the glass transition and density of the alloy, indicating a reduction of free volume in the BMG alloy with annealing time. Compared with the as-cast sample, the fracture strength, Vickers hardness, viscosity, Young’s modulus, and stress-relaxation stability of the annealed BMGs increase with annealing time, which is caused by the reduction of free volume in the annealed samples. Furthermore, a change of fracture morphology from a mixture of smooth and furrow zones in the as-cast sample to a mainly furrow zone in the sample annealed for 8 h was also observed. All samples exhibit brittle behavior during tension tests.

Optical second-harmonic generation (SHG) was applied to study the ferroelectric and magnetic properties of strained epitaxial BiFeO3 films deposited on (001) SrTiO3 substrates by metal organic chemical vapor deposition. A strong interplay between the ferroelectric and magnetic subsystems of bismuth ferrite films results in the pronounced temperature dependence of the SHG intensity. The decrease of the critical temperature of the ferroelectric phase transition and the expansion of the nonlinear transient area near Néel temperature were observed for the strained BiFeO3 films.

Al85Ni9Nd4Co2 metallic glass/nanostructured ribbons and powders were used as starting materials for producing bulk amorphous/nanostructured Al-based alloys. Glassy ribbons were obtained by melt spinning at wheel surface velocities ranging from 5 to 37 m/s. The amorphous ribbons exhibited a supercooled liquid region of ∼20 K, a reduced glass transition temperature of ∼0.47 and γ ∼ 0.328. Mechanical alloying of the elemental powder mixture did not lead to amorphization. However, amorphous powders obtained by milling the glassy ribbons for 9 h exhibited a thermal stability similar to the initial ribbons. Isothermal differential scanning calorimetry measurements were used to determine the consolidation parameters of the glassy powders. Consolidation at 513 K by uniaxial hot pressing and hot extrusion indicated that the former method leads to bulk glassy samples, whereas the latter one yields nanostructured α-Al/glassy matrix composites.

Two different types of metallic glasses, a metal-metal-based and a metal-metalloid-based one, in both bulk and ribbon form (i.e., produced with very different quenching rates) are compared with respect to their structural relaxation behavior during continuous heating (2 K/min) in a vibrating-reed set-up (frequencies 0.2–5 kHz). The variation of damping as a function of temperature, time, and strain amplitude is shown as a measure of the content of structural relaxation centers, whose nature is studied by means of artificially introduced irregularities into the amorphous structure (i.e., by cold rolling and by hydrogen charging). The results indicate that the hydrogen damping peak, which is only observed in the Zr-based glass, is more probably due to hydrogen reorientation jumps than due to reorientation of hydrogen-related, dislocation-like distortion fields although the latter cannot be ruled out. A pronounced deformation damping peak could not be found in contrast to earlier results in the literature, probably owing to the selected degrees of deformation.

Zn1−xMnxS nanoparticles with x = 0.08, 0.16, and 0.32 were synthesized by a coprecipitation reaction between nitrate and sodium sulfide at room temperature in air. The magnetic properties of the Zn1−xMnxS nanoparticles were investigated by alternating-current (ac) susceptibility and direct-current (dc) magnetization measurements. The Mn3O4 phase was observed to exist in the Zn1−xMnxS nanoparticles as x ⩾ 0.16. The actual concentrations (x) of Mn-doped ZnS nanoparticles were determined by energy-dispersive x-ray analysis (EDAX) to be 0.06, 0.11, and 0.20, respectively, corresponding to the initial concentrations x = 0.08, 0.16, and 0.32. All the nanoparticles had the cubic structure and the lattice constant of Zn1−xMnxS phase increased with increasing Mn dopant concentration. For the Zn0.68Mn0.32S nanoparticles, there was evidence for appearance of cluster spin-glasslike behavior, as indicated by two maxima around 15 and 25 K in temperature dependence of ac susceptibility. The frequency independence of the peak at higher temperature is related to the intracluster ferromagnetic (FM) interactions, and the frequency dependence of the peak at lower temperature is associated with the spin glass. All the results revealed that the concentration of Mn2+ in Mn–ZnS and the amount of Mn3O4 were crucial for the cluster spin-glass behavior, which was not found when the real concentration (x) was unequal to 0.20 in Zn1−xMnxS.

A method is introduced to determine the depth distribution of the residual stresses in (Ti,Al)N films. The films were gradually stripped by chemical corrosion, an optical system was designed to test the curvature change of the specimens, and the depth distribution of the residual stresses was calculated. The results show that the residual stresses increase gradually from the interface of film/substrate and reach a maximum value at the middle region, then decrease until the surface.