In the search for a Pb-free compatible under-bump-metallization (UBM) barrier material, magnetron sputtering of a nonmagnetic nickel silicon alloy (NiSi) target was used to deposit a low-stress polycrystalline NiSi thin film. In the reaction with SnAg3.0Cu0.5 solder, NiSi was found to have greatly reduced reaction and intermetallics (IMC) formation rates compared with sputtered NiV. A continuous layer of IMCs in NiSi UBM-solder joint remains stable after 10 reflows and 1000 h thermal aging tests, resulting in preferred bulk solder failure mode in ball shearing/pull testing. Our results demonstrate that NiSi is a highly promising thin film barrier material suitable for Pb-free solder bumping.

We report here on the utilization of variable band gap conjugated polymers for optoelectronic redox applications comprising organic photovoltaics, color tunable light emitting diodes, and electrochromics. For the evaluation of morphology in photovoltaicdevices, atomic force microscopy, and optical microscopy provided direct visualization of the blend film structure. The evolution of the morphology in two and three component blends incorporating poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenlenevinylene] (MEH-PPV), poly(methylmethacrylate) (PMMA), and [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) was investigated. It was found that while insulating PMMA can be used to modulate the phase separation in these blends, a bicontinuous network of donor and acceptor was required to achieve the best device results. Similarily, a MEH-PPVcopolymer with a decreased conjugation length has been used for investigating inter- and intramolecular photoinduced charge transfer in the presence of PMMA and PCBM.We fabricated MEH-PPV/PCBM solar cells that have power conversion efficiencies up to 1.5% with a range of 0.7–1.5%, dependent on the nature of the MEH-PPV used. This further indicates that in addition to blend morphology, polymer structure is critical for optimizing device performance. To this end, the concept of an ideal donor for photovoltaic devices based on poly[2,5-di(3,7-dialkoxy)-cyanoterephthalylidene] is described and two donor-acceptor polymers based on cyanovinylene (CNV) and dioxythiophene are discussed as representative examples of soluble narrow band gap polymers synthesized in our group. For light emitting applications, utilization of two blue emitting conjugated polymers poly (9,9-dioctylfluorene) (PFO) and poly[(9,9-dihexylfluorenyl-2,7-diyl)-co-(9,ethyl-3,6-carbazole)] (PFH-PEtCz)is presented for a color tunable polymer light emitting diode that emits orange, green, and blue light with a voltage range of 7–10 V as a function of the total conjugated polymer content in PMMA and is attributed to the phase separation between the conjugated polymers. Finally, the narrow band gap conjugated polymer, poly[bis(3,4-propylenedioxythiophene-dihexyl)]-cyanovinylene has been characterized for its electrochromic properties, illustrating the multifunctional nature of variable band gap conjugated polymers.

Epitaxial anatase TiO2 thin films were successfully grown on lattice-matched SrTiO3 (001) substrates by a novel hydrothermal method at very low temperatures (120–200 °C). This method is extremely simple and inexpensive in that the SrTiO3 substrate itself provides the source material for the TiO2 film. X-ray diffraction confirmed the high crystallinity and phase purity of the anatase films. The epitaxial relationship between the film and the substrate was determined as (001)[100]anatase // (001)[100]SrTiO3. Atomic force microscopy revealed the average size of the anatase crystallites as approximately 50 to 200 nm.

Transparent conductive In-doped Cd3TeO6 thin films were deposited on silica glass substrate by radio frequency magnetron sputtering using targets composed of CdO, TeO2, and In2O3 powders, and their electrical and optical properties were examined. The electrical resistivity of 3.2 × 10−3 Ωcm and an average transmittance above 80% in the visible region (400–800 nm) were obtained for the films deposited at the substrate temperature above 300 °C. The maximum optical band gap was 3.92 eV for the film deposited at 700 °C, demonstrating a large optical band gap comparable to indium tin oxide.

Chorioamnion, the membrane surrounding a fetus during gestation, is a structural soft tissue critical for maintaining a successful pregnancy and delivery. However, the mechanical behavior of this tissue membrane is poorly understood. The structural component of chorioamnion is the amnion sublayer, which provides the membrane’s mechanical integrity via a dense collagen network and is the focus of this investigation. Amnion uniaxial and planar equi-biaxial tension testing was performed using cyclic loading and stress-relaxation. Cyclic testing demonstrated dramatic energy dissipation in the first cycle followed by less hysteresis on subsequent cycles. Fractional energy dissipation per cycle was strain dependent, with greatest dissipation at small strain levels. Stress-relaxation testing demonstrated a level-dependent response and continued relaxation after long relaxation times. A nonlinear viscoelastic (separable) hereditary integral approach was inadequate to model the amnion response due to intrinsic coupling of the strain- and time-dependent responses.

Preliminary investigations of a new high-strength alloy of composition Fe30Ni20Mn25Al25 (at.%) are described in this paper. The as-cast alloy consisted of a periodic two-phase microstructure of interconnected, ∼50-nm-wide rods with fully coherent {100} interfaces, strongly suggestive of formation by a B2 to [(B2 + body-centered cubic (bcc)] spinodal decomposition. The (Ni,Al)-rich B2 and (Fe,Mn)-rich bcc phases differed in lattice parameter by <0.5%. Hardness and yield strength of the as-cast alloy were found to be approximately 500 VPN and 1500 MPa, respectively, and increased by more than 50% after annealing at 550 °C for several days. (Fe,Mn)-rich precipitates with a β–Mn structure were observed in the annealed material.

Nacre, the inner layer of mollusk shells is a composite made of platelets of mineral aragonitic calcium carbonate with a few weight percent organic material sandwiched in between. The organic and nanostructural nuances are often suggested to be the reason for the extreme toughness of nacre. Here we report the presence of interlocks between platelets of nacre from red abalone. We also report and show, using three-dimensional finite element modeling, that interlocks are the key mechanism for the high toughness and strength of nacre. The observed rotation between platelet layers, which were earlier reported as defects of structure, are necessary for the formation of interlocks.

High electric fields were delivered to specimens during imaging in the transmission electron microscopy (TEM) chamber to reveal details of electric field-induced phenomena in ferroelectric oxides. These include the polarization switching in nanometer-sized ferroelectric domains and the grain boundary cavitation in a commercial lead zirconate titanate (PZT) polycrystalline ceramic, the domain wall fracture in a Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal, and the transformation of incommensurate modulations in Pb0.99Nb0.02[(Zr1−xSnx)1−yTiy]0.98O3 (PZST100x/100y/2) polycrystalline ceramics. In the PZT ceramic, a cavitation process was uncovered for the electric field-induced intergranular fracture. In the ferroelectric single crystal, a preexisting crack was observed to deflect and to follow a 90° domain wall, indicating the presence of severe incompatible piezoelectric strains at thedomain wall. In the antiferroelectric PZST ceramics, the electric field-induced antiferroelectric-to-ferroelectric phase transformation was accompanied with the disappearance of incommensurate modulations.

The alanates (complex aluminohydrides) have relatively high gravimetric hydrogen density and are among the most promising solid-state hydrogen-storage materials. In this work, the crystal structure and electronic structure of pure and mixed-alkali alanates were calculated by ground-state density-functional band-structure calculations. The results are in excellent correspondence with available experimental data. The properties of the pure alanates were compared, and the relatively high stability of the Li3AlH6 phase was pointed out as an important difference that may explain the difficulty of hydrogenating lithium alanate. The alkali alanates are nonmetallic with calculated band gaps around 5 eV and 2.5–3 eV for the tetra- and hexahydrides. The bonding was identified as ionic between the alkali cations and the aluminohydride complexes, while it is polar covalent within the complex. A broad range of hypothetical mixed-alkali alanate compounds was simulated, and four were found to be stable compared to the pure alanates and each other: LiNa2AlH6, K2LiAlH6, K2NaAlH6, and K2.5Na0.5AlH6. No mixed-alkali tetrahydrides were found to be stable, and this was explained by the local coordination within the different compounds. The only alkali alanate that seemed to be close to fulfilling the international hydrogen density targets was NaAlH4.

The oxidation kinetics of Cu60Zr30Ti10 bulk metallic glass and its crystalline counterpart were studied in oxygen environment over the temperature range of 573–773 K. The oxidation kinetics, measured with thermogravimetric analysis, of the metallic glass follows a linear rate law between 573 and 653 K and a parabolic rate law between 673 and 733 K. It was also found that the oxidation activation energy of metallic glass is lower than that of its crystalline counterpart. The x-ray diffraction pattern showed that the oxide layer is composed of Cu2O, CuO, ZrO2, and metallic Cu. Cu enrichment on the topmost oxide layer of the metallic glass oxidized at 573 K was revealed by x-ray photoelectron spectroscopy while there was a decrease in Cu content in the innermost oxide layer. The oxide surface morphologies observed from scanning electron microscopy showed that ZrO2 granules formed at low temperatures while whiskerlike copper oxides formed at higher temperatures.

Band-structure calculations of germanium carbide (GeC) show that it is a new indirect wide band gap semiconducting material, which crystallizes in both cubic and hexagonal phases. Through the density functional and total-energy technique in the generalized gradient approximation, the two polytypes 3C and 2H of GeC were studied. According to our calculations, it is a hard material with a percentage of covalency of about 80–90%. Important energy gaps were determined. The bulk modulus, density of states, and charge density were calculated. For the bulk modulus calculations, Murnaghan’s equation of state was used under elastic deformation to measure hardness. Our calculations showed that this semiconducting material crystallizes in zincblend (Eg = 1.76 eV) and wurtzite (Eg = 2.5 eV) structures.

Nanocrystalline Ni–Zn ferrite particles (Ni0.5Zn0.5Fe2O4) have been successfully produced by microemulsion method. The microemulsion process was first observed by transmission electron microscopy examination. The particles exhibit a blocking temperature of 95 K. They do not attain saturation magnetization even at a high field of 50 KOe. The saturation magnetization at 300 K is 29.8 emu/g, which is significantly lower than that reported for the bulk ceramic standard. Below the blocking temperature, the Ni0.5Zn0.5Fe2O4 nanocrystalline particles exhibit a hysteretic feature. The remanent magnetization and coercivity at 2K are 10.45 emu/g and 453 Oe, respectively.

In situ observation is of great value in the study of radiation damage utilizing electron or ion irradiation. We summarize the facilities and give examples of work found around the world. In situ observations of irradiation behavior have fallen into two broad classes. One class consists of long-term irradiation, with observations of microstructural evolution as a function of the radiation dose in which the advantage of in situ observation has been the maintenance of specimen position, orientation, and temperature. A second class has involved the recording of individual damage events in situations in which subsequent evolution would render the correct interpretation of ex situ observations impossible. In this review, examples of the first class of observation include ion-beam amorphization, damage accumulation, plastic flow, implant precipitation, precipitate evolution under irradiation, and damage recovery by thermal annealing. Examples of the second class of observation include single isolated ion impacts that produce defects in the form of dislocation loops, amorphous zones, or surface craters, and single ion impact-sputtering events. Experiments in both classes of observations attempt to reveal the kinetics underlying damage production, accumulation, and evolution.

Transparent ceramic scintillators of La2Hf2O7:Ti4+ were developed by a novel combustion synthesis method. The optical transmittance for a 1.0-mm-thick specimen is about 60% of the incident light, and the x-ray stopping power is also quiet high. The broad emission band centered at 475 nm originates from the oxide-Ti4+ charge-transfer transitions, which renders fast decay time on the order of 10 μs. The highest relative light output has reached about 1.5 times that of Bi4Ge3O12 (BGO) single crystal when excited by 120 kV x-rays.

Mechanically alloyed Mo44Si26Ta5Zr5Fe3Co12Y5 multicomponent glassy alloy exhibits an exceptionally high glass transition temperature of 1202 K and a crystallization temperature of 1324 K, as well as an ultrahigh hardness of 18 GPa. This example is used to demonstrate metallic glasses that possess extraordinary thermal stability and ultrahigh strength and, at the same time, a wide supercooled liquid region (122 K) that is needed for processing into bulk forms through powder metallurgy routes.

Uniform and thermally stable spherical titania particles with hollow interiors were directly prepared by a novel solvothermal precipitation of TiCl4 in isopropanol without templates or shape-controller reagents. An average particle size of 700 nm to 1 μm was obtained. The hollow spheres consisted of pure anatase phase nanocrystals with an estimated crystallite size of 12–15 nm. Upon heating, the pure anatase phase was retained for temperatures up to 800 °C, which suggested that the spherical structure contributed to phase stability. This method is a promising process for industrial-scale preparation of titania hollow spheres.

The microstructure and orientation relationships of epitaxial (111)-oriented SrTiO3 thin films grown by radio frequency magnetron sputtering on epitaxial (111)-oriented Pt/Ti electrodes on sapphire were investigated using x-ray diffraction, conventional and scanning transmission electron microscopy. We show that the epitaxial growth of (111)-oriented SrTiO3 films was promoted by thin Ti adhesion layers underneath the Pt electrode. The SrTiO3 films nucleated with two twin-related orientation variants, rotated by 180° about the 〈111〉 surface normal. The twin boundaries were oriented approximately normal to the film plane, but no strong preference for a specific boundary plane was observed. Growth mechanisms and the relationships to the dielectric properties are discussed.

Dislocation nucleation in solid solutions of face-centered-cubic metallic materials was studied using nanoindentation. The effects of solute impurities in the copper–nickel system on the formation of dislocations in a previously dislocation-free region were demonstrated to be minimal. The shear stress required to nucleate dislocations in copper is approximately 1.6 GPa, while in nickel a 3.9 GPa shear stress is required. Changes in shear stress for nucleation track closely with changes in elastic modulus showing the nucleation stress is approximately 1/30 to 1/20 of the shear modulus. The expected solid-solution strengthening is identified within the same experimental method, demonstrating unambiguously the fact that solid-solution impurities in this system will impact the propagation of dislocations during plastic deformation but not alter the homogeneous nucleation of dislocations in these materials.

It was found that after treatment under 10T magnetic field and temperature 900 °C the bending strength of NiAl–Cr(Mo)–Hf alloy is increased by about 75%. The fracture section observation shows that the specimens' ductility is enhanced by the magnetic field treatment. Electron probe microanalysis shows that after treatment of the magnetic field the Heusler phases at NiAl/Cr(Mo) grain boundaries are partially dissolved and the small Heusler phases particles at Cr(Mo) and matrix phases interfaces almost dissolved into NiAl matrix.

The dielectric properties of goethite and, in particular, the changes during the topotactic conversion of goethite to hematite were studied from room temperature to about 800 °C in the frequency range of 400 to 3000 MHz using the cavity perturbation technique. The complex permittivity, that is, both the real and the imaginary or absorptive parts (έ and ἕ), were measured under various heating regimens. In addition, thermogravimetric analysis (TGA) was performed to characterize the transformation of goethite to hematite. The Debye relaxation formalism was applied to the processes occurring both during and after the main dehydroxylation reaction to calculate the relaxation times. The Arrhenius equation for thermally activated relaxation times was used to determine the activation energies. Both the real and the absorptive parts of the permittivity exhibited a significant peak during the main part of the goethite to hematite decomposition reaction. Above the transformation, there was another, less dramatic, thermally activated increase in the permittivity values. The increase in the permittivities during the goethite to hematite transformation was attributed to the formation of quasi-free migrating radicals, for example, hydroxyl ions, oxygen ions, or hydrogen atoms, during the dehydroxylation of goethite. The derivative thermogravimetric analysis (DTGA) curve was found to be directly related to the transient values of the real and the imaginary permittivities. Higher heating rates resulted in an accelerated rate of dehydroxylation and therefore higher values of the transient permittivities. In the temperature range of 400 °C to 500 °C (i.e., just above the dehydroxylation peak), the real permittivity exhibited a varying frequency dependence, which suggested that changes were occurring in the newly formed, highly defected hematite structure, which is referred to as hydrohematite. During the reaction there were multiple relaxation processes and thus the Debye relationship could not be applied. However, at temperatures above about 500 °C, the structure stabilized, the Debye relationship was more closely followed, and the relaxation times could be determined as a function of temperature. The activation energy for the relaxation process above 500 °C was determined to be 0.47 kJ/mol.