The undercooling of flip-chip Pb-free solder bumps was investigated by differential scanning calorimetry (DSC) to understand the effects of solder composition and volume, with and without the presence of an under bump metallurgy (UBM). A large amount of the undercooling (as large as 90 °C) was observed with Sn-rich, flip-chip size solder bumps sitting in a glass mold, while the corresponding undercooling was significantly reduced in the presence of a wettable UBM surface. In addition, the solidification of an array of individual solder bumps was monitored in situ by a video imaging technique during both heating-up and cooling-down cycles. Data obtained by the optical imaging method were used to complement the DSC thermal measurements. A random solidification of the array of bumps was demonstrated during cooling, which also spans a wide temperature range of 40–80 °C. In contrast, an almost simultaneous melting of the bumps was observed during heating.

This paper describes a new method to synthesize AlN nanowires by the nitridation of Ti3Si0.9Al0.1C2 solid solution. Single-crystalline AlN nanowires with the hexagonal wurtzite structure can be easily prepared using this method. In particular, the resulting AlN nanowires display a new growth orientation of 〈1011〉 besides 〈1000〉 and 〈0001〉. This work indicates that MN+1AXN compounds are promising raw reactants to synthesize one-dimensional (1D) nanostructures of nitrides and oxides.

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.

Manganese (Mn) grows in a metastable expanded (c/a > 1) face-centered-tetragonal (fct) phase on thin fct-Co(001) template films. A layer-by-layer growth mode is observed for small Mn thicknesses. Antiferromagnetism (AFM) of fct-Mn is evidenced by the observation of shifted magnetization loops antiparallel to the cooling field direction (negative bias) and enhanced coercive fields for Co/Mn bilayers. At low temperature, magnetic exchange interactions are detected at the Co/Mn interface for nominal Mn thicknesses as low as 1.4 monolayer (ML), indicating the onset of AFM in 2-ML-thick Mn islands. However, between 2- and 5-ML Mn, a positive bias of the magnetization loops is observed in a certain temperature range below the blocking temperature (TB) of the films. This peculiar behavior is explained by the dependence of TB on both the local Mn ML thickness and the Mn island size, leading to a unidirectional coercivity enhancement in a temperature range where both blocked and unblocked regions coexist in the Mn layers.

The Sm-based Sm–Al–Ni glass-forming system was investigated using our e/a- and cluster-related criteria. Three bulk metallic glasses (BMGs) Sm54Al23Ni23, Sm56Al22Ni22, and Sm58Al21Ni21 were obtained by suction casting into rods with a diameter of 3 mm. All of them shared a constant e/a = 1.5 and fell along the e/a-constant composition line in the ternary composition chart. The Sm54Al23Ni23 BMG exhibiting the largest Trg was located at the intersection point of the e/a-constant line and the Sm7Ni3-Al cluster line, with thermodynamic parameters of Tg = 548 K at a heating rate of 20 K/min, Tg/Tm = 0.634, and Tg/Tl = 0.615. The Sm7Ni3 cluster was a capped trigonal prism derived from the SmNi phase.

An in situ electrical measurement technique for the investigation of nanoindentation using a Hysitron Triboindenter is described, together with details of experiments to address some technical issues associated with the technique. Pressure-induced phase transformations in silicon during indentation are of particular interest but are not fully understood. The current in situ electrical characterization method makes use of differences in electrical properties of the phase-transformed silicon to better understand the sequence of transformations that occur during loading and unloading. Here, electric current is measured through the sample/indenter tip during indentation, with a fixed or variable voltage applied to the sample. This method allows both current monitoring during indentation and the extraction of current-voltage (I-V) characteristics at various stages of loading. The work presented here focuses on experimental issues that must be understood for a full interpretation of results from nanoindentation experiments in silicon. The tip/sample contact and subsurface electrical resistivity changes dominate the resultant current measurement. Extracting the component of contact resistance provides an extremely sensitive method for measuring the electrical properties of the material immediately below the indenter tip, with initial results from indentation in silicon showing that this is a very sensitive probe of subsurface structural and electrical changes.

Highly sinter-active powders of RE2O3 [rare earth (RE) = Gd, Eu, Dy] have been prepared using the corresponding metal nitrates as the oxidants, and glycine and citric acid as the fuels. Two different oxidant-to-fuel ratios, namely stoichiometric ratio and fuel-deficient ratio were used to explore the possibility of preparing different crystallographic modifications. By a careful control of oxidant-to-fuel ratio, nanocrystalline Eu2O3 and Gd2O3 could be prepared in cubic (C-type) as well as monoclinic (B-type) modifications. However, the high-temperature monoclinic modification could not be obtained for Dy2O3 due to a very high C-to-B-type phase transition temperature. The crystallite size, surface area, and sintering behavior were also studied for powders prepared using different oxidant-to-fuel ratios, and the results showed a remarkable correlation between different fuel contents and powder properties. Some of these powders resulted in pellets of nearly theoretical density. The sintered microstructure was studied by scanning electron microscopy.

Surface and planar defect structures of γ-Al2O3 nanorods synthesized by the arc-discharge method were studied by means of high-resolution transmission electron microscopy and image simulation. Our investigation showed that there was a high number density of twins in the nanorods. We suggested a possible configuration of {111} twins in γ-Al2O3, and this model fit our experimental result well. In some nanorods, the ordering of nanotwins gave rise to a local hexagonal-like structure. The twinned nanorods were usually enclosed by {100} and {111} facets, and their growth direction was changed from 〈110〉 into 〈111〉. The surface structures of the nanorods confirmed that the {111}-type surface should be more stable.

The in situ Raman spectroscopy technique was used to investigate the ion transport and to determine the concomitant electrochemical tuning of Fermi level in single-wall carbon nanotubes. The variation of structural bonding in a single-wall carbon nanotube bundle dipped in aqueous alkaline earth halide electrolyte such as CaCl2 with electrochemical biasing was monitored. This is because Raman scattering can detect changes in C–C bond length through radial breathing mode (RBM) at ∼184 cm−1, which varies inversely with the nanotube diameter and the G band at ∼1590 cm−1, varying with the axial bond length. Consistent reversible and substantial variation in Raman intensity of both modes was induced by electrode potential point at the fine and continuous tuning (alternatively, emptying/depleting or filling) of the specific bonding and anti-bonding molecular states. Qualitatively, the results were explained in terms of changes in the energy gap occurring between the one-dimensional van Hove singularities present in the electron density of states, possibly arising due to the alterations in the overlap integral of π bonds between the p orbitals of the adjacent carbon atoms. We estimated the extent of variation of the absolute potential of the Fermi level and overlap integral (γ0) between the nearest-neighbor carbon atoms by modeling the electrochemical potential dependence of Raman intensity. Observations also suggested that the work function of the tube becomes larger for the metallic nanotubes in contrast to the simultaneously present semiconducting nanotubes.

The formation of synthesized Si2N2O nanowires using the process of Si nitridation depending on the addition of carbon was investigated. The diameter of the Si2N2O nanowires having a high aspect ratio of about 50–80 nm was found in the porous Si2N2O–Si3N4 substrate to which 6 wt% C was added. The synthesized Si2N2O nanowires had orthorhombic single-crystal structure covered with a thin (∼2 nm thick) amorphous layer and a large number of stacking faults along the (2 0 0) plane. The photoluminescence spectrum of Si2N2O nanowires showed a strong, stable green emission at 540 nm.

Calcium phosphate coatings prepared using the technique of electron beam deposition were immersed in a simulated body fluid for different periods of time to determine their response in vitro. The amorphous as-deposited coatings dissolved completely after a few days of immersion. After annealing in air at 700 °C, the dissolution of a small amount of amorphous phase in the crystalline coatings promotes the precipitation of bonelike apatite on the recessed regions by increasing the local supersaturation of calcium and phosphate ions. Formation of apatite was confirmed by the x-ray diffraction peaks at (200), (211), and (203) planes which grew after immersion in simulated body fluid. Fourier transform infrared results conformed to this with the increase in intensity of the absorption band at 1450 cm−1, signifying the increase in carbonate content. Scanning electron microscopy results showed spherical-shaped apatite nucleated on dissolved surface after 8 days of immersion. Sixteen days after immersion, almost 80% of the surface area was covered with apatite formation and grew to coalesce between neighboring particles forming an integrated platelike layer after 28 days. No obvious detachment between the grown layer and the underlying coating was observed.

A hierarchical computational method has been developed and used with a finite-element microstructurally based dislocation density multiple-slip crystalline formulation to predict how nanoindentation affects behavior in face-centered cubic crystalline aggregates at scales that span the molecular to the continuum level. Displacement profiles from molecular dynamics simulations of nanoindentation were used to obtain scaling relations, which are based on indented depths, grain-sizes, and grain aggregate distributions. These scaling relations are then used to coarsen grains in a microstructurally based finite-element formulation that accounts for dislocation density evolution, crystalline structures, and grain-sizes. This computational approach was validated with a number of experimental measurements pertaining to single gold crystals. This hierarchical model provides a methodology to link molecular level simulations with a microstructurally based finite element method formulation that can be used to ascertain inelastic effects, such as shear-slip distribution, pressure accumulation, and dislocation density and slip-rate evolution at physical scales that are commensurate with ductile behavior at the microstructural scale.

In a hydrophobic zeolite, the infiltration and defiltration of water can be controlled by adjusting external pressure, and therefore the system behaves as a “liquid spring.” Since the hysteresis of sorption isotherm is negligible and the working pressure is thermally controllable, volume memory devices can be developed based on this phenomenon. With the addition of sodium chloride, both infiltration and defiltration pressures increase, which should be attributed to the cation exchange. The temperature sensitivity of the system increases with the electrolyte concentration, beneficial to improving the output energy density.

We present a laser-assisted spray pyrolysis method to fabricate nanoparticle coatings of metal oxides. In this process, 1.5-μm size droplets of a titanium- or iron-containing organometallic precursor were injected into a vacuum chamber with SF6 carrier gas. The strong absorption of a 3W CO2 laser beam focused onto the injector tip in the presence of SF6 increased the temperature of the gas and the droplets to about 300 °C. Films deposited on heated substrates with and without the CO2 laser heating were studied by atomic force microscopy. The laser heating of the droplets caused the solvent to evaporate before depositing on the substrate, leading to grain sizes that are about a factor of 3 smaller than those deposited without laser heating. By controlling the concentration of the precursor in the solvent, the average particle sizes have been tuned from 80 to 50 nm.

Plane strain indentation of a single crystal by a rigid wedge is analyzed using discrete dislocation plasticity. We consider two wedge geometries having different sharpness, as specified by the half-angle of the indenter: α = 70° and 85°. The dislocations are all of edge character and modeled as line singularities in a linear elastic material. The crystal has initial sources and obstacles randomly distributed over three slip systems. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles, and dislocation annihilation are incorporated through a set of constitutive rules. Several definitions of the contact area (contact length in plane strain) are used to illustrate the sensitivity of the hardness value in the submicron indentation regime to the definition of contact area. The size dependence of the indentation hardness is found to be sensitive to the definition of contact area used and to depend on the wedge half-angle. For a relatively sharp indenter, with a half-angle of 70°, an indentation size effect is not obtained when the contact area is small and when the hardness is based on the actual contact length, while there does appear to be a size effect for some hardness values based on other measures of contact length.

Polychromatic synchrotron x-ray microdiffraction is used to determine the epitaxy of YBa2Cu3Ox (YBCO) films grown on polycrystalline Y.15Zr.85O1.925/CeO2/Y2O3/Ni95W5(Ni) rolling-assisted, biaxially textured substrates (RABiTS). A novel analysis technique is introduced in which the orientation of mosaic films is measured by using a Hough transform to recognize arcs in Laue microdiffraction patterns that correspond to low-index zone axes. While the overall epitaxy is cube-on-cube, grain-by-grain analysis reveals a systematic misorientation of YBCO with respect to Ni: the YBCO [001] rotates toward the direction of the surface normal. The crystal mosaic (for rotation about the rolling direction) measured by a single diffraction pattern sampling a 0.5-μm2 surface area is 0.7° full width at half-maximum for YBCO grown on Ni grains with a low tilt; for more highly tilted grains, the YBCO patterns can no longer be measured, presumably due to the large mosaic. The YBCO mosaic over the entire area of a Ni grain is ∼2.5° and varies with grain size; the mosaic is smaller for larger grains.

The advantages of depositing AlN–SiC alloy transition layers on SiC substrates before the seeded growth of bulk AlN crystals were examined. The presence of AlN–SiC alloy layers helped to suppress the SiC decomposition by providing vapor sources of silicon and carbon. In addition, cracks in the final AlN crystals decreased from ∼5 × 106/mm2 for those grown directly on SiC substrates to less than 1 × 106/mm2 for those grown on AlN–SiC alloy layers because of the intermediate lattice constants and thermal expansion coefficient of AlN–SiC. X-ray diffraction confirmed the formation of pure single-crystalline AlN upon both AlN–SiC alloys and SiC substrates. X-ray topography (XRT) demonstrated that strains present in the AlN crystals decreased as the AlN grew thicker. However, the XRT for AlN crystals grown directly on SiC substrates was significantly distorted with a high overall defect density compared to those grown on AlN–SiC alloys.

Nanoporous titania (TiO2) or titania nanotubes could provide a continuous nanostructured electron-conducting anode for organic photovoltaics. In this work, nanoporous titania was formed by anodizing thin films of titanium on both glass and transparent conducting oxide (TCO) substrates. Titanium thin films (500–700 nm) were deposited by radio frequency (RF) magnetron sputtering. Films were anodized in acidic electrolytes containing small amounts of hydrofluoric acid (HF) at constant voltages ranging from 7 to 15 V. Scanning electron microscope (SEM) analysis revealed a nanoporous structure. Nanoporous titania structures were grown on glass in an electrolyte containing sulfuric acid, trisodium citrate, and potassium fluoride, with pore diameters around 50 nm. Analyzing the films at different anodization times, the stages of nanopore formation were elucidated. Additionally, nanoporous titania was formed on a TCO substrate by anodizing in an electrolyte containing acetic acid and hydrofluoric acid. While not completely transparent, the nanoporous titania is promising for use in organic photovoltaics.

The electrochemical stability of LiCoO2 thin films was improved by cerium-phosphate coating deposited at room temperature. The cerium-phosphate coating layer also effectively suppressed the increase of charge-transfer resistance during cycling. However, the cycling stability and the initial capacity of the coated LiCoO2 thin films deteriorated as the annealing temperature increased, different from other metal-phosphate coating. These phenomena were attributed to the interdiffusion between the cerium-phosphate coating layer and LiCoO2 thin film, instead of the nanocrystal formation in the amorphous coating layer.

The Sn/Cu/Sn/Cu/Sn sandwich-type couples prepared by the casting method are used for examining the effects of electromigration on Sn/Cu interfacial reactions. The samples are reacted at 170 and 180 °C for 24–240 h by passing an electric current with a density of 5000 A/cm2. At the interfaces where electrons flow from the Sn side to the Cu side, uniform layers of Cu6Sn5 and Cu3Sn are formed. The results are similar to those without passage of an electric current. The relatively thicker Cu6Sn5 layer is attributed to the extra Cu source from the dissolved Cu during the sample preparation. At the interfaces where electrons flow from the Cu side to the Sn side, large and nonplanar Cu6Sn5 phase regions are formed. Formation of large Cu6Sn5 regions is the result of electromigration-enhanced Cu diffusion through the grain boundaries and surfaces.