In this investigation on the formation of multiple-layered Kirkendall voids at Cu/Sn–3.5Ag solder joints, Sn–3.5Ag solder balls were reacted with Cu under bump metallurgy (UBM), which was electroplated using bis-sodium sulfopropyl–disulfide, C6H12O6S4Na2 (SPS) additive. The sequence of multilayer Kirkendall voids and Cu–Sn IMC (intermetallic compounds) formations are explained with the aid of cross-sectional scanning electron microscopy (SEM) micrographs and schematic diagrams. During the aging treatment at 150 °C, layers of Cu6Sn5/Cu3Sn formed at the solder joints and Kirkendall voids nucleated at the Cu3Sn/Cu interface as a result of the segregation of residual S originating from SPS. However, with Kirkendall void growth, the net section area of the Cu/Cu3Sn interface decreased and the Cu flux into Cu3Sn was inhibited. As the atomic ratio of Cu against Sn in the Cu3Sn dropped, transformation of Cu3Sn into Cu6Sn5 ensued. Subsequent diffusion of Sn atoms into the remaining Cu UBM through the remaining ligament of the Cu6Sn5/Cu interface precipitated secondary Cu3Sn beneath the primary Cu3Sn/Cu interface, and the secondary Kirkendall voids formed at the new Cu3Sn/Cu interface and so on.

We demonstrated the growth of indium nitride (InN) nanowires on Si(111) substrates by metalorganic chemical vapor deposition without the use of any intermediate GaN or AlN buffer layer. The InN nanowires were grown by forming the Au + In droplets and In droplets on the Au- and In-coated Si substrate. The growth conditions such as chamber pressure, chamber temperature, reaction gas flow rate, and carrier gas flow rate were optimized to yield nanowires free from contamination. Depending on the growth parameters different growth regimes for the InN nanowires were identified. The strength of self-catalytic route has been highlighted. The morphology and microstructures of samples were characterized by x-ray diffraction and scanning electron microscopy (SEM). The transmission electron microscopy and SEM investigations showed that the InN nanowires are single crystals with diameters ranging from 40 to 400 nm, and lengths up to 3 µm. Photoluminescence spectra of the InN nanowires showed a strong broad emission peak at 0.77 eV.

The idea of first-principles methods is to determine the properties of materials by solving the basic equations of quantum mechanics and statistical mechanics. With such an approach, one can, in principle, predict the behavior of novel materials without the need to synthesize them and create a virtual design laboratory. By showing several examples of new electrode materials that have been computationally designed, synthesized, and tested, the impact of first-principles methods in the field of Li battery electrode materials will be demonstrated. A significant advantage of computational property prediction is its scalability, which is currently being implemented into the Materials Genome Project at the Massachusetts Institute of Technology. Using a high-throughput computational environment, coupled to a database of all known inorganic materials, basic information on all known inorganic materials and a large number of novel “designed” materials is being computed. Scalability of high-throughput computing can easily be extended to reach across the complete universe of inorganic compounds, although challenges need to be overcome to further enable the impact of first-principles methods.

The synthesis of hexagonal aluminum nitride (AlN) nanoparticles and nanowhiskers by using direct nitridation of aluminum powders is presented in this work. After mixing aluminum powders with carbon and silica (derived from rice bran ashes) at a cryogenic temperature, the homogeneous mixture was heat treated/examined in a differential scanning calorimeter/tube furnace under N2 atmosphere. Under a maximum temperature of 1450 °C in N2 atmosphere, the as-milled aluminum-carbon-silica powder mixtures transformed completely into AlN nanoparticles and nanowhiskers with a trace of graphite. The formation mechanisms for AlN nanoparticles and nanowhiskers are discussed.

This work first deals with the effect of Nb addition on the liquid phase separation in the Cu–Co system, which displays a metastable liquid miscibility gap. The isothermal sections at 800, 900, 1000, 1100, and 1200 °C in the Cu–Co–Nb system have been experimentally determined by optical microscopy, electron probe microanalysis, and x-ray diffraction on the equilibrated alloys, and the phase equilibria in the Cu–Co–Nb ternary system were thermodynamically assessed by using CALPHAD (Calculation of Phase Diagrams) method on the basis of the presently determined experimental data. Nb additions can stabilize the metastable liquid phase separation in the Cu–Co binary system and significantly increase its critical temperature. The solidified Cu–Co–Nb alloys appearing on the top-bottom separated microstructural morphology under low cooling rate while forming core-type macrostructural morphology under high cooling rate have been confirmed.

Secondary-ion mass spectrometry (SIMS) was used to study the profile characteristics and diffusion properties of Mg, Ti, and Er ions in photorefractive-damage-resistant locally Er/Mg-diffused near-stoichiometric (NS) Ti:Mg:Er:LiNbO3 strip waveguides fabricated on two Z-cut initially congruent, undoped LiNbO3 substrates in sequence by local Er doping at 1100 °C or 1130 °C in air, Mg/Ti pre-diffusion at 1100 °C in wet O2, and post Li-rich vapor transport equilibration (VTE) treatment at 1100 °C. For comparison, a SIMS study was also carried out on the waveguides fabricated without the post-VTE treatment. In order to compensate for the refractive index decrease arising from both the Mg doping and the post-VTE treatment, and hence to get a positive net index increment profile in the Ti-diffused layer, a thicker Ti-film of around 170 nm was coated. Nevertheless, SIMS results show that the Ti diffusion reservoir, as well as the Er and Mg reservoirs, was exhausted. From the SIMS profiles, characteristic diffusion parameters such as the 1/e diffusion width (for Ti only) and depth, diffusivity, and surface concentration of the Mg, Ti, and Er ions are obtained. It is interesting that the Mg distribution in the NS waveguide layer is desirably homogeneous with a concentration [(1.7–2.0) ± 0.3 mol%] higher than the optical damage concentration threshold. The Ti profile follows a sum of two error functions along the lateral direction of NS waveguides with a diffusion width of (12–13) ± 0.5 μm, and a Gaussian function in the depth direction with a 1/e depth of (5.1–6.0) ± 0.2 μm. The Er profile follows also a Gaussian function with a 1/e depth of (3.7–4.4) ± 0.3 μm. In the NS waveguide layer, the mean diffusivity is (7.1 ± 2.2) to (8.3 ± 2.8) μm2/h for Mg, (3.5 ± 0.3) to (4.5 ± 0.4) μm2/h in the lateral direction and (0.54 ± 0.04) to (1.13 ± 0.08) μm2/h in the depth direction for Ti, and (4.1 ± 0.4) to (5.5 ± 0.5) × 10−2 μm2/h for Er. The effects of Li outward diffusion in the initial Er doping procedure, and the Mg codiffusion and post-VTE treatment on the mean Mg, Ti, and Er diffusivities are discussed in comparison with the previously reported results on single Mg, Ti, or Er diffusion and Mg/Ti codiffusion in a pure or homogeneously MgO-doped congruent LiNbO3 crystal. Finally, the keys to the success of the fabrication procedure adopted are discussed.

We investigated the structural stabilities of the intermetallics and the solid-state phase transformations induced by lattice vibration effects in the Al–Zr system by first-principles calculations. The calculated lattice parameters of all the phases and the phonon dispersion relations for pure Al and Zr are in good agreement with the experimental data. AlZr(oC8), Al4Zr5 (hP18), and Al3Zr5 (tI32) are predicted to be the high-temperature phases. To study the structural stabilities at high temperatures, the thermodynamic properties of the intermetallics are calculated via the linear response approach within the harmonic approximation. Thanks to the calculated enthalpies of formation at high temperatures, Al3Zr5 is predicted to be stabilized above 1163 K with respect to AlZr2 and Al2Zr3, in good agreement with the phase transformation temperature (1273 K) in the experimental phase diagram.

Electromigration activation energy is measured by a built-in sensor that detects the real temperature during current stressing. Activation energy can be accurately determined by calibrating the temperature using the temperature coefficient of resistivity of an Al trace. The activation energies for eutectic SnAg and SnPb solder bumps are measured on Cu under-bump metallization (UBM) as 1.06 and 0.87 eV, respectively. The activation energy mainly depends on the formation of Cu–Sn intermetallic compounds. On the other hand, the activation energy for eutectic SnAg solder bumps with Cu–Ni UBM is measured as 0.84 eV, which is mainly related to void formation in the solder.

The distribution of alloying elements and the corresponding structural evolution of Mn–Sb alloys in magnetic field gradients were investigated in detail. It was found that a high magnetic field gradient could control the distribution of solute element in the alloys during the solidification process and therefore resulted in the coexistence of both primary MnSb and Sb phases or the aggregation of the primary MnSb with a continuous change in morphology. The positions where these primary phases located depended on the direction of field gradient. The control of the solute element distribution by a high magnetic field gradient was realized through the magnetic buoyancy force that could drive the migration of Mn element in the melt, originating from the difference in the magnetic susceptibility between Mn and Sb. The effectiveness of this control depends on the alloy composition, specimen dimension, cooling rate, and |BdB/dz| value.

Solid solutions 0.7Bi1−xLax (Fe0.9Cr0.1) O3–0.1BaTiO3–0.2PbTiO3 (BLxFOC-BT-PT, with x = 0, 0.03, 0.05, 0.07) solid solutions were prepared by the traditional ceramic process. X-ray diffraction results reveal that all samples show pure pseudocubic perovskites structure. The lattice parameter of the solid solutions increases linearly with the La content, indicating that La ions have entered crystal lattices to form a solid solution. The Curie temperature of the solid solutions decreases with the La content. Room-temperature polarization–electric field (P–E) curves indicate that the samples with x = 0.03 and 0.05 exhibit saturated P–E loops. Piezoelectric constant d33 of the solid solutions increases firstly and then decreases. Magnetizations of the solid solutions decrease with the La content. The evidence of weak ferromagnetism and saturated ferroelectric hysteresis loops in BLxFOC–BT–PT system at room temperature makes it a good candidate for multiferroic applications.

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The structural, transport, and magnetotransport properties of single-phase, homogeneous nanostructured La0.7Sr0.3MnO3 (LSMO) manganites synthesized by the coprecipitation route were investigated and the effect of sintering temperature on the microstructure of LSMO compounds was studied. A strong dependence of transport and magnetotransport behavior on the microstructure and nature of grain boundaries has been observed in the single-phase LSMO sintered at various temperatures. High-field magnetoresistance (HFMR) at room temperature is found to increase [13% (LS6) to 25% (LS9)] while low temperature (5 K) magnetoresistance decreases [75% (LS6) to 46% (LS9)] under 9 T field with increase in sintering temperature, which has been attributed to the spin-polarized tunneling and spin-dependent scattering of charge carriers.

Much of the interaction of a material with its environment is governed by its surface, and modulation of the material's surface characteristics can vastly broaden its range of application. This review focuses on the tailoring of surfaces of materials to achieve specific changes in their responses to external stimuli to enhance their prospects for applications in the biomedical field. Combining the inherent properties of different classes of materials such as polymers, metals, mesoporous materials, and magnetic nanoparticles with a responsive surface presents unique opportunities. Applications include surface-modified filters for the effective adsorption and separation of biomolecules, materials for the promotion of cell adhesion or detachment for cell sheet engineering and regenerative medicine, actuators, or valves, and vehicles for the controlled and targeted delivery of therapeutic agents. The commonly used external stimuli are heat, pH, and light, and these, as well as electrical stimulation used in conjunction with conducting polymers, will be addressed in this review. Progress in the field of responsive surfaces has been rapid, and continuing research can be expected to result in more innovative and exciting developments. Nevertheless, much work remains to be done to meet the challenges in the translation of these systems from the laboratory to clinical applications.

Transparent glass ceramics containing Li2MgSiO4: Cr4+ nanocrystallites were prepared. Intense broadband near-infrared emission with full width at half-maximum larger than 200 nm and long fluorescence lifetime (τ > 100 μs) were observed. The temperature-dependent optical characteristics of the glass ceramics containing Li2MgSiO4: Cr4+ crystallites were compared to those of Li2MgSiO4: Cr4+ single crystals. The reason for extra-long near-infrared fluorescence lifetime was illuminated by the mixed effect between 3T2 and 1E levels. The crystal-filed-induced particular energy-level scheme makes the fluorescence lifetime of the glass ceramics containing Li2MgSiO4: Cr4+ crystallites one order longer than those of other Cr4+-doped glass ceramics.

This paper reports the development of nonwoven nanofibers of pure and iron-doped titanium dioxide (TiO2) and evaluation of their antimicrobial attributes for using them as disinfectant gauze for wound healing upon brief activation by ultraviolet/infrared (UV/IR) illumination. It was found that the fibers exhibited superior bactericidal affinity when exposed briefly (3–12 s) to either multiphoton laser or infrared radiations. On the other hand, exposure to a UV beam for up to 20 min was not effective in mitigating the bacterial colonization of the Escherichia coli.

Responsive materials cover a breadth of types and many application fields. The common feature in all cases is a nonlinear change in properties or behavior as a result of a stimulus. The material response can range from a simple change in conformation or ionization state, through to phase transitions, bulk aggregation, or complete dissolution. As a consequence, sensing and actuation are the most investigated functions of these materials. In this issue, we have chosen to focus on responsive materials as exemplified by externally switchable, environmentally activated, and reversibly or controllably triggered systems. The chemistries of these materials, their physical properties, functional behavior, and activity are all linked, so we have aimed to cover the many disciplines underlying responsive materials through articles featuring areas that already span disparate research topics. These areas include drug delivery, smart surfaces, and nanotube transducers. The responsive materials field is growing in excitement as well as activity, and we hope that readers will gain an insight into this fascinating branch of materials science through this MRS Bulletin issue.

Fe1–xCx coatings were synthesized by triode magnetron sputtering of an iron target in a methane/argon atmosphere with a large range of composition (x = 0.3 to 0.6 ± 0.06). Film surfaces were characterized by grazing incidence x-ray diffraction, scanning and transmission electron microscopies, and electron energy loss spectroscopy, to study effects of the variation of the methane gas flow rate on their structural properties. The coatings were constituted of the ε-Fe3C carbide (x = 0.3 and 0.36), in which carbon atoms are in octahedral sites, and of nanocomposite structure constituted of disordered and crystalline carbide nanograins embedded in a carbon matrix made of an amorphous and poorly crystallized graphenelike material (x = 0.55 and 0.60). In situ annealing of the nanocomposite Fe0.45C0.55 coating led to the formation of carbides θ-Fe3C and Fe7C3 (with carbon atoms in prismatic sites) and C-rich cubic carbide possibly related to the τ2-Fe2C7 compound.