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Effects of Zn addition on the interfacial reaction between Sn and Ni(P) were investigated by systematically varying the Zn concentration in the Sn solder. It was found that the typical Ni–Sn reaction product, Ni3Sn4 phase, was changed substantially by adding small amounts of Zn to the Sn. With the Zn addition, the ternary Ni4(Sn1−x,Znx) phase formed at the interface during reflow and aging according to X-ray diffraction analysis. In the Ni4(Sn1−x,Znx) phase, the lattice parameters contracted with increasing Zn content, in agreement with the Vegard's law. Since diffusions of the reactive species through the denser ternary intermetallic compound were more unlikely than through the binary Ni3Sn4, the Zn-containing solder showed a much slower electroless Ni–P consumption rate than Sn. The decrease in Ni consumption rate increased with the increasing Zn content in Sn. The reason for the decrease was that the growth rate of Ni4(Sn1−x,Znx) phase was directly determined by substitution of Zn atoms into the Sn sublattice.

Composite photocatalysts of palladium oxide and nitrogen-doped titanium oxide (PdO/TiON) were synthesized by a solgel process, as convenient forms of nanopowder or immobilized powder on nanofiber. The PdO/TiON catalysts were tested for visible-light-activated photocatalysis using different bacterial indicators, including gram-negative cells of Escherichia coli and Pseudomonas aeruginosa, and gram-positive cells of Staphylococcus aureus. Disinfection data indicated that PdO/TiON composite photocatalysts have a much better photocatalytic activity than either palladium-doped (PdO/TiO(2)) or nitrogen-doped titanium oxide (TiON) under visible-light illumination. The roles of Pd and N were discussed in terms of the production and separation of the charge carriers under visible light illumination. The photocatalytic activity was thus dependent on dopants and light intensity. Microscopic characterization demonstrated that visible-light photocatalysis on PdO/TiON caused drastic damage on the bacteria cell wall and the cell membrane.

P, N, and Mo ternary co-doped nano TiO2 photocatalysts ((P, N, Mo)-TiO2) were prepared by a single step sol–gel method, which show much enhanced photocatalytic activities over Mo-TiO2, (P, N)-TiO2, un-doped TiO2 and Degussa P25 under visible light irradiation. The degradation rate of 0.72Mo–P-TiO2 is as high as 65.3%, which is about 6.7 times of that of Degussa P25. Possible reasons for the improvement of photocatalytic activities were analyzed.

Tensile stress–strain response of an equal channel angularly pressed (ECAPed) Sn–3.8Ag–0.7Cu alloy was investigated to seek a mechanistic understanding of the time-dependent deformation in Sn-rich alloys. It was found that the deformation behavior of the ECAPed alloy had a stronger rate-dependence than the as-cast alloy. At low strain rates, the ECAPed alloy exhibited a higher ductility but a lower flow stress. During tensile deformation, the equiaxed Sn grains were stretched into thin strips. In comparison, the slip steps were primary feature within single grain at high strain rates. The enhanced rate-dependence of the ECAPed alloy was related to greater tendency for grain boundary diffusion due to the increase in the grain boundary density.

The first-principles density-functional calculation was conducted to investigate the electronic band structures of titanium dioxide with heavy nitrogen doping (TiO2−x N x ). The calculation results indicate that when x ⩽ 0.25, isolated N 2p states appear above the valence-band maximum of TiO2 without a band-gap narrowing between O 2p and Ti 3d states. When x ⩾ 0.50, an obvious band gap narrowing between O 2p and Ti 3d states was observed along with the existence of isolated N 2p states above the valence-band of TiO2, indicating that the mechanism proposed by Asahi et al operates under heavy nitrogen doping condition.

Polarity effect on the interfacial reactions from high-density electric currents was investigated in a solder interconnect with a large disparity in the effective charge between the solder constituents. A reverse polarity effect was found where the intermetallic compound layer at the cathode grew significantly thicker than that at the anode under electric loading. Such an abnormal polarity effect was shown to result from electromigrations of Sn and Zn along opposite directions as dictated by the disparity in their effective charges. As Sn migrated to the anode under electron wind force, the resulting back stress drove Zn atoms to drift to the cathode. A kinetic analysis of the Zn mass transport explained the differential growth of the intermetallic compounds at the two electrodes, in good agreement with the experimental data.

Electromigration in the Ni/Sn-Zn/Cu solder interconnect was studied with an average current density of 3.51 × 104 A/cm2 for 168.5 h at 150°C. When the electrons flowed from the Ni side to the Cu side, uniform layers of Ni5Zn21 and Cu5Zn8 were formed at the Ni/Sn-Zn and Cu/Sn-Zn interfaces. However, upon reversing the current direction, where electron flow was from the Cu side to the Ni side, a thicker Cu6Sn5 phase replaced the Ni5Zn21 phase at the Ni/Sn-Zn interface, whereas at the Cu/Sn-Zn interface, a thicker β-CuZn phase replaced the Cu5Zn8 phase.

A novel nonequilibrium approach combining low-temperature reactive sputtering and rapid thermal annealing was developed to resolve the opposing requirements on crystallization and high dopant concentration for creating nitrogen-doped TiO2 (TiON) thin film with a mixture of anatase and rutile phases. The dual-phase TiON has a higher visible-light absorption and a smaller band gap than pure anatase TiON. Its superior photocatalytic performance was demonstrated by the highly hydrophilic conversion and faster photodegradation of organic pollutants under visible-light illumination. Our work demonstrates that the crystal structure is a major factor in determining the visible-light photocatalytic activity of TiON.

Cyclic stress–strain response of an equal channel angularly pressed Sn-3.8Ag-0.7Cu alloy was investigated to seek a mechanistic understanding of cyclic softening in Sn-rich alloys. The equal channel angular pressing (ECAP) was applied to modify the microstructure of the solder alloy by breaking up the needlelike Ag3Sn intermetallic phase into fine granules and by reducing the large β-Sn dendrites into smaller and equiaxed grains. The extruded alloys were subjected to strain-controlled fatigue test at various strain amplitudes. It was found that the extruded alloy exhibited a sharp decrease of the stress amplitude within the initial few cycles compared with the as-cast alloy. After only a few cycles, the alloy suffered from noticeable surface damage. In situ scanning electron microscopy observations of the cyclic bending specimens revealed an approximately logarithmic relationship between crack density and the number of cycles. A theoretical model of microcrack accumulation was constructed to explain the rapid cyclic softening behavior. The predicted results, based on the model, agreed well with the experimental data and indicated that the rapid softening had resulted from an increased tendency for grain boundary cracking in the ECAPed microstructure due to the increase in the grain boundary area per unit volume and the reduced resistance of Ag3Sn to grain boundary sliding.

Palladium-modified nitrogen-doped titanium oxide (TiON/PdO) nanofibers were synthesized by a sol–gel process on activated carbon-coated glass fiber (ACGF) template. The TiON/PdO fiber was tested for visible-light-activated photocatalysis using Bacillus subtilis endospore as a target. Our work shows that TiON/PdO nanofibers display an effective antimicrobial effect on Bacillus spores. The palladium modification provides a strong enhancement over TiON in the photocatalytic disinfection. Microscopic characterization demonstrated that visible-light photocatalysis on TiON/PdO fiber caused drastic damage on the spore coat and internal structure.

The photoresponse of TiO2 in nitrogen and oxygen under visible light was studied. The TiO2 Was synthesized by a new sol-gel process using Ti(OBu)(4) and ethanolamine, while the research was focused on the effect of calcining temperature on the photoresponse of the TiO2 film. It was observed a strong photoresponse of the TiO2 at a light wavelength of approximately 480 nm in room temperature when calcined at temperature from 450 to 500,C. On the contrary, the photoreponse was very weak for TiO2 calcined at temperature less than 400 degrees C or more than 550 degrees C. Thermal gravimetry-differential scanning calorimeter-mass spectrometer (TG-DSC-MS) measurement showed that there was a significant weight loss (about 18 wt.%) of the TiO2 precursor calcined in the temperature range from 400 to 470 degrees C, which was due to the oxidation of the residual impurities in the TiO2. The evolved gases were primarily composed of H2O and CO2. In conclusion, it is suggested that the strong photoresponse of the TiO2 under visible light is due to the impurities, such as carbon or hydrocarbon compound which mixed with or adhered on the TiO2, as well as the microporous structure in the TiO2 film (C) 2008 Elsevier BY. All rights reserved.

The optical and photocatalytic properties of a photonic crystal structure were examined to elucidate the origin of the enhanced visible light absorption from semiconductor photonic crystals. Both an enhancement in visible light absorption and an increase of the photoactivity of the semiconductor photocatalyst were found when a photonic crystal layer was decoupled from the photocatalytic film. The decoupling clearly shows that the optical enhancement arose from the dielectric mirror effect of the photonic crystal. As such, the enhancement was maximized by matching the high light absorbance region of photocatalytic semiconductors with the characteristic photonic band gap of the decoupled photonic crystal layer under various illumination conditions. For enhanced visible light photocatalytic activity, the decoupled photonic crystal layer does not have to be made from the same light-harvesting materials, but can be synthesized by a wide range of materials for ease of the fabrication process.

Niobium pentaoxide (Nb2O5) and nitrogen co-doped TiO2 photocatalysts were prepared by mechanical alloying with Nb2O5, TiO2 and urea as raw materials. The pure TiO2 powders of Degussa P25 were chosen as precursor. Chemical and physical properties of the Nb2O5 and N co-doped TiO2 photocatalysts were investigated, including XRD patterns, XPS spectra, DRS spectra, FT-IR spectra and N2 adsorption-desorption isotherms. Experiments on photodegradation of methylene blue (MB) and sulfosalicylic acid (SSA) under visible light were carried out to evaluate the photoactivities of the prepared samples, and the chemical oxygen demand (COD) analysis was also conducted as a comparison.

Heavy nitrogen doping of TiO2 thin films has been achieved by ion-beam-assisted deposition. The heavily doped films have a distorted anatase crystal structure and show an increase in visible-light absorption compared to films with only light nitrogen doping. The enhanced absorption is shown by a first-principles density-functional calculation to result from an electronic band-gap narrowing, in contrast to the appearance of isolated N 2p states above the valence-band maximum that occur with light nitrogen doping.

Nitrogen-doped titanium oxide inverse opal structure was synthesized to combine both chemical and physical modifications on n-TiO2 by the polystyrene sphere self-assembly followed by a sol–gel process. Enhanced visible-light absorption and subsequently enhanced photodegradation efficiency were observed in this unique structure, which can be attributed to both nitrogen-doping effect and inverse opal structure effect. Our work suggests that the coupling of photonic band gap structure with photocatalytic materials is a promising approach to achieve maximum enhancement for various photocatalytic materials, especially for environmental applications and solar cell devices.

Nano-sized nitrogen-doped Ti-W mixed oxides (N-TiO2-x%WO3) were prepared by soft chemical method, and their intrinsic characteristics were investigated using XRD, TEM, N2 adsorption and desorption isotherms, UV-Vis diffuse reflectance spectra and XPS. Experiments on photodegradation of Methylene Blue (MB) under visible light irradiation were carried out to evaluate the photocatalytic abilities of N-TiO2-x%WO3. Chemical Oxygen Demand (COD) analysis was also performed to evaluate the mineralization abilities of N-TiO2-x%WO3. It is shown that the N-TiO2-x%WO3 exhibited higher COD removing rates compared with Degussa P25. The color bleaching rates of N-TiO2-x%WO3 were equal to that of Degussa P25. The enhanced photocatalytic activities were probably related to the strong absorption abilities of the N-TiO2-x%WO3.

Electrodeposited Ag film was explored as a potential interfacial barrier to Bi segregation for suppressing the interfacial embrittlement of Cu/SnBi interconnects. The presence of Ag film introduced Ag3Sn intermetallic layer at the interface, which effectively prevented Bi from reaching the Cu/intermetallic interface. When the persistent slip bands (PSBs) in the Cu single crystal were driven to impinge the Cu/Cu3Sn interface, interfacial cracking was averted and instead superceded by cracking of intermetallic compounds (IMCs) at the interface.

Wetting of electroless nickel by the eutectic SnAgCu solder alloy was investigated in the as-deposited and annealed conditions. In the as-deposited state, P content in the nickel had a minimal effect on the solderability of the electroless nickel. Upon annealing, numerous nickel phosphide particles precipitated out of the electroless nickel with a high-P content. The presence of these phosphide precipitates reduced the solderability of the electroless nickel both in terms of the wetting force and wetting kinetics. While weakening in the wetting force is related to the inferior contact condition, the slower wetting kinetics is explained in terms of the reduction in the dissolution rate of the electroless nickel from non-soluble phosphide particles. (c) 2007 Elsevier B.V. All rights reserved.

Nitrogen was doped into titanium dioxide film to alter its surface electrostatic properties, and subsequently modulate the interaction force between MS2 virus and semiconductor films for control of the adsorption behavior of MS2 on semiconductor surfaces. By combining atomic force microscopy (AFM) height profile and phase profile, adsorptions of MS2 virus on TiO2-based semiconductor surfaces were observed in solutions over a range of pH values. The adsorption behavior was shown to agree with the theoretical analysis of colloidal interactions.

Interfacial reactions in a eutectic Sn–Zn solder/Cu interconnect were investigated under electric current stressing. After applying a constant direct current at 4.26 × 104 A cm−2 for 166 h, an abnormal “polarity effect” was found where the intermetallic compound layer at the cathode was about 2.3 μm thicker than that at the anode. Upon increasing the temperature to about 185 °C, Cu–Zn compounds were replaced by Cu–Sn compounds at the anode and by a mixture of Cu–Zn and Cu–Sn compounds at the cathode.

Structural changes from high-density electric currents were examined in a eutectic In-Sn/Cu interconnect. Under electrical loading, Sn and In migrated in opposite directions, creating a partition of the Sn- and In-rich phases between the anode and the cathode. At the anode, a net gain of Sn atoms resulted in the formation of massive, columnar hillocks on the surface, but a net loss of In led to dissolution and disappearance of the In-rich intermetallic layer. At the cathode, the exodus of Sn left valleys adjacent to the In-rich regions on the surface, while the amount of the In-rich phase grew, due to the net influx of In at the expense of the In-rich intermetallic layer.

Low cycle fatigue behavior of Sn-3.8Ag-0.7Cu solder was investigated under fully reversed cyclic loading, with particular emphasis on microstructural effects. The LCF behavior of the solder with equiaxed microstructure was found to differ greatly from that of the solder with a dendrite microstructure. At a given total strain amplitude, the dendrite microstructure exhibited a much longer fatigue life than the equiaxed microstructure. Such a strong microstructural effect on fatigue life arose from the difference in cyclic deformation and fracture mechanisms between the two microstructures. A large number of microcracks along grain boundaries of the equiaxed structure solder developed with increasing cycling, while for the dendrite structure solder, cyclic deformation took place along the direction of the maximal shear stress during fatigue tests and microcracks initiated and propagated along shear deformation bands. Besides, the fatigue behavior of the dendritic microstructure was very sensitive to cyclic frequency whereas the fatigue behavior of the equiaxed microstructure showed less sensitivity to cyclic frequency.

A solvothermal method is described for preparing nanomaterials of titanium oxide with different morphologies. Nanostructures, such as wire, rod, cube, and fiber, were synthesized in mass quantities by controlling either the concentrations of the precursor or growth temperature and introducing different additives in one simple system based on titanium tetroisopropoxide and ethylene glycol. Hydrothermal treatment of the base system produced nanowires with diameters around 40 nm. The addition of ethylenediamine (EDA) to the system inhibited the radial expansion of the nanowires, resulting in nanorods and nanofibers with diameters down to about 2 nm. Increasing the EDA concentration tended to induce mesoscale self-assembly of nanofibers into arrays. The presence of water promoted the formation of nearly spherical nanoparticles with sizes dependent on the EDA concentration. At higher temperatures, the same system yielded well-defined nanobelts or nanocubes. The replacement of EDA by 2,4-pentanedione favored the formation of nanosheets while tetramethylammonium hydroxide appeared to confuse the growth of nanorods, creating a continuous network.

The eutectic Sn3.8Ag0.7Cu alloy is widely considered a leading Pb-free replacement for the eutectic Pb-Sn solder alloy in electronic packaging where creep deformation and rupture is a major concern. In this study, creep rupture behavior of Sn-Ag-Cu solder alloy was investigated under the isothermal condition. Creep tests were conducted under a range of stresses and temperatures. Creep lifetime data were analyzed by the combined time-temperature equations following the Sherby, Larsen-Miller, and Manson-Haferd approaches. From these analyses, a series of material parameters were obtained from the experimental data. The results showed that the Manson-Hanferd method provided a better correlation with the creep rupture data. The mechanisms of creep deformation and rupture at different time-temperature combinations are discussed.

Nitrogen-doped titanium oxide (TiON) nanoparticle photocatalysts were synthesized by a sol−gel process, for disinfection using E. coli as target bacteria. Our work shows that the calcination atmosphere has strong effects on the composition, structure, optical, and antimicrobial properties of TiON nanoparticles. Powders calcinated in a flow of N2 atmosphere (C−TiON) contain free carbon residue and demonstrate different structures and properties compared to the TiON powders calcinated in air. Disinfection experiments on Escherichia coli indicate that C−TiON composite photocatalyst has a much better photocatalytic activity than pure TiON photocatalyst under visible light illumination. The enhanced photocatalytic activity is related to stronger visible light absorption of the carbon-sensitized TiON.

Carbon doped titanium dioxide photocatalysts have been synthesized by a precipitation method. Anatase TiO2 was obtained when the precipitate was heat-treated at 400°C when rutile phase appeared at 600°C. The absorption spectra of the powders showed strong absorption in visible region. For the sample calcined at 400 °C , the absorption extended up to 750nm. X-ray photoelectron spectrum (XPS) confirmed that carbon atoms were incorporated into the TiO2 crystal lattice. Photodegradation experiments showed that the powders had visible-light degradation activity.

Weakening of Pb-free solder joints by high-density electric currents was investigated by combining electromigration experiments with micromechanical testing. Prolonged exposure of the Sn3.5Ag0.7Cu/Cu interconnects to electric currents resulted in hillock formation on the sample surface. After electromigration, the strength of the solder joint was reduced by nearly half. However, the strength loss was recoverable by thermal annealing of the electromigration damage.

Superparamagnetic nanocatalysts could minimize both the external and internal mass transport limitations and neutralize OH(-) produced in the reaction more effectively to enhance the catalytic nitrite reduction efficiency with the depressed product selectivity to undesirable ammonium, while possess an easy magnetic separation capability. However, commonly used qusi-monodispersed superparamagnetic Fe3O4 nanosphere is not suitable as catalyst support for nitrite reduction because it could reduce the catalytic reaction efficiency and the product selectivity to N2, and the iron leakage could bring secondary contamination to the treated water. In this study, protective shells of SiO2, polymethylacrylic acid, and carbon were introduced to synthesize Fe3O4@SiO2/Pd, Fe3O4@PMAA/Pd, and Fe3O4@C/Pd catalysts for catalytic nitrite reduction. It was found that SiO2 shell could provide the complete protection to Fe3O4 nanosphere core among these shells. Because of its good dispersion, dense structure, and complete protection to Fe3O4, the Fe3O4@SiO2/Pd catalyst demonstrated the highest catalytic nitrite reduction activity without the detection of NH4(+) produced. Due to this unique structure, the activity of Fe3O4@SiO2/Pd catalysts for nitrite reduction was found to be independent of the Pd nanoparticle size or shape, and their product selectivity was independent of the Pd nanoparticle size, shape, and content. Furthermore, their superparamagnetic nature and high saturation magnetization allowed their easy magnetic separation from treated water, and they also demonstrated a good stability during the subsequent recycling experiment.

One-dimensional nanomaterials may organize into macrostructures to have hierarchically porous structures, which could not only be easily adopted into various water treatment apparatus to solve the separation issue of nanomaterials from water but also take full advantage of their nanosize effect for enhanced water treatment performance. In this work, a novel template-based process was developed to create Mn3O4/CeO2 hybrid nanotubes, in which a redox reaction happened between the OMS-2 nanowire template and Ce(NO3)3 to create hybrid nanotubes without the template removal process. Both the Ce/Mn ratio and the precipitation agent were found to be critical in the formation of Mn3O4/CeO2 hybrid nanotubes. Because of their relatively large specific surface area, porous structure, high pore volume, and proper surface properties, these Mn3O4/CeO2 hybrid nanotubes demonstrated good As(III) removal performances in water. These Mn3O4/CeO2 hybrid nanotubes could form paper-like, free-standing membranes spontaneously by a self-assembly process without high temperature treatment, which kept the preferable properties of Mn3O4/CeO2 hybrid nanotubes while avoiding the potential nanomaterial dispersion problem. Thus, they could be readily utilized in commonly used flow-through reactors for water treatment purposes. This approach could be further applied to other material systems to create various hybrid nanotubes for a broad range of technical applications.

The development of highly efficient As(iii) adsorbents is critical to largely simplify the arsenic treatment process and lower its cost. For the first time, SnO2 nanospheres were demonstrated to possess a highly efficient As(iii) adsorption capability from water in a near neutral pH environment as predicted by the material criterion we recently developed for the selection of highly efficient arsenic adsorbents. These SnO2 nanospheres were synthesized by a simple and cost-effective hydrolysis process with the assistance of ethyl acetate under ambient conditions, which had a good dispersity, a narrow size distribution, a relatively large specific surface area, and a porous structure. A fast As(iii) adsorption was observed in the kinetics study on these SnO2 nanospheres, and their Langmuir adsorption capacity was determined to be ∼112.7 mg g(-1) at pH ∼7. The As(iii) adsorption mechanism on SnO2 nanospheres was examined by both macroscopic and microscopic techniques, which demonstrated that it followed the inner-sphere complex model. These SnO2 nanospheres demonstrated effective As(iii) adsorption even with exceptionally high concentrations of co-existing ions, and a good regeneration capability by washing with NaOH solution.

Through silicon via (TSV) is a critical element for three-dimensional (3D) integration of devices in vertically multilevel stack-die microelectronic packages. In this paper, the microstructure evolution of TSV-Cu under thermal cycling was studied and the topography of TSVs under thermal cycling tests was examined by white light interferometer. It was found that the Cu was intrude inside the Si die during the test, and the intrusion height increased with cycle time and leveled off at 0.72µm and 0.53µm for upside and backside after 210 cycles, respectively. Besides, the Cu intrusion height at the Cu/Si interface is greater than that in the middle of Cu bar. in addition, cracks were observed at SiO 2 /Ta barrier interface and between BEOL line and Cu vias. It suggests that diffusional creep of the interface is the key for Cu via intrusion, the residual stress and thermal stress drive the interfacial sliding at interfaces.

Sn–Ag–Cu solder/copper single crystal joints were prepared to reveal the interfacial fatigue damage mechanisms. Scallop-type Cu 6 Sn 5 and planar-type Cu 6 Sn 5 /Cu 3 Sn intermetallic compounds (IMCs) interfaces were formed between SnAgCu solder and copper single crystal after re-flowing at 240 °C and subsequent aging at 170 °C, respectively. Under cyclic loading, persistent slip bands (PSBs) were activated in copper single crystal and continuously impinged the interfaces of the SnAgCu solder/copper single crystal joint. Two types of fatigue cracking modes, i.e. interfacial cracking between solder and IMC and fracture within IMC, were observed. Based on the experimental observations above, the corresponding interfacial fatigue cracking mechanisms were discussed.

Recent fatigue studies of Sn-rich Pb-free solder alloys are reviewed to provide an overview of the current understanding of cyclic deformation, cyclic softening, fatigue crack initiation, fatigue crack growth, and fatigue life behavior in these alloys. Because of their low melting temperatures, these alloys demonstrated extensive cyclic creep deformation at room temperature. Limited amount of data have shown that the cyclic creep rate is strongly dependent on stress amplitude, peak stress, stress ratio and cyclic frequency. At constant cyclic strain amplitudes, most Sn-rich alloys exhibit cycle-dependent and cyclic softening. The softening is more pronounced at larger strain amplitudes and higher temperatures, and in fine grain structures. Characteristic of these alloys, fatigue cracks tend to initiate at grain and phase boundaries very early in the fatigue life, involving considerable amount of grain boundary cavitation and sliding. The growth of fatigue cracks in these alloys may follow both transgranular and intergranular paths, depending on the stress ratio and frequency of the cyclic loading. At low stress ratios and high frequencies, fatigue crack growth rate correlates well with the range of stress intensities or J-integrals but the time-dependent C* integral provides a better correlation with the crack velocity at high stress ratios and low frequencies. The fatigue life of the alloys is a strong function of the strain amplitude, cyclic frequency, temperature, and microstructure. While a few sets of fatigue life data are available, these data, when analyzed in terms of the Coffin–Mason equation, showed large variations, with the fatigue ductility exponent ranging from −0.43 to −1.14 and the fatigue ductility from 0.04 to 20.9. Several approaches have been suggested to explain the differences in the fatigue life behavior, including revision of the Coffin–Mason analysis and use of alternative fatigue life models.

Isothermal annealing was applied to an equal-channel angularly pressed (ECAP) Cu-Fe-P alloy to investigate the stability of the fine-grained microstructure. The starting as-cast microstructure of the alloy contained two sets of second phase particles, fine gamma-Fe particles, and coarse Fe3P intermetallic particles. Following ECAP, while the fine Fe particles were well dispersed in the interior of the grains, many Fe3P particles were found outside the grains, along or at the junctions of grain boundaries. The presence of Fe3P particles at the grain boundaries enhanced the stability of the fine grain structure by delaying grain growth until 873 K when a coarse-grained structure developed. The different roles of the two sets of particles are discussed in terms of the difference in their deformation behavior. (c) 2006 Elsevier B.V. All rights reserved.

Effect of electromigration on the interfacial structure of solder interconnects was examined in a Sn-Bi/Cu interconnect system. At current densities above 104 A/cm2, Bi migrated along the direction of the electron flow in the solder alloy. A continuous Bi layer was found at the solder interface on the anode side, while a Sn-rich region formed at the cathode side of the electrical connection. The presence of the Bi layer inhibited further growth of Cu-Sn intermetallic phase at the interface by acting as a diffusion barrier to the reacting species.

The potential for extending the optical absorption range of TiO2 by doping with nonmetallic elements was examined in nitrogen-containing TiO2 thin films. Thin films of TiO2-xNx were synthesized on glass and silicon substrates by ion-beam-assisted deposition to obtain a wide range of nitrogen concentrations. The compositions of the films were determined by Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy. The structures of the films were analyzed by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. The optical properties of the films were measured by UV-Vis spectroscopy and ellipsometry. A characteristic decreasing trend in band-gap values of the films was observed within a certain range of increasing dopant concentrations. As the nitrogen concentration increased, the structure of the films evolved from a well-defined anatase to deformed anatase. The reduced band gaps are associated with the N 2p orbital in the TiO2-xNx films.

A dense population of voids was found along the interface between Cu3Sn and Cu following prolonged aging. The voids appeared only on the Cu3Sn/Cu interface that had been covered by roughly monolayer of Bi segregant. Void formation was related to vacancy condensation after the segregant took up vacancy sinks.

A new experimental technique for accelerated fatigue testing has recently been developed (Du, T.B., Liu, M., Seghi, S., Hsia, K.J., Economy, J. and Shang, J.K. 2001. “Piezoelectric Actuation of Crack Growth along Polymer-Metal Interfaces in Adhesive Bonds,’’ Journal of Material Research, 16(10):2885-2892). Using a piezoelectric actuator, cyclic loading can be applied at frequencies up to 20 kHz, several orders of magnitude higher than that achieved by a conventional mechanical cyclic loading technique. Moreover, the new technique using piezoelectric actuators directly addresses the debonding problem in piezoelectric multilayered smart structures. However, the threshold energy release rate for interfacial crack propagation, evaluated based on plane strain and linear piezoelectricity assumptions in (Du, T.B. 2001. “Durability of Polymer/Metal Interfaces under Cyclic Loading,” PhD Thesis, University of Illinois at Urbana-Champaign, Urbana, IL, May), seems to be almost an order of magnitude lower than that measured by the conventional mechanical cyclic loading. In this article, we investigate the origin of such discrepancies, and find that the driving force provided by piezoelectric actuator is intrinsically three-dimensional in nature. To account for this effect, we develop both a plane strain model and a modified plane strain analytical model that takes into account the effects in the third dimension to evaluate the energy release rate. The results show that the plane strain solution underestimates the driving force. We also study the effect of nonlinear piezoelectricity on crack driving forces by performing detailed finite element simulations. The results show that the nonlinear piezoelectric effect is another important factor that contributes to the discrepancy between the results from the piezoelectric loading and that from the conventional mechanical loading.

Fracture resistance of the interface between electroless Ni(P) and the eutectic SnBi solder alloy was examined in the as-reflowed and aged conditions, to investigate the potential role of Ni in inhibiting interfacial segregation of Bi in SnBi–Cu interconnect. In the as-reflowed condition, the fracture resistance of the SnBi/Ni(P) interface was about the same as that of the SnBi/Cu interface. Upon aging at 120 °C for 7 days the fracture resistance of the SnBi/Ni(P) interface was much higher than that of the SnBi/Cu interface. Such a difference was shown to result from the difference in fracture mechanism as the crack remained along the solder–intermetallic interface in the aged SnBi–Ni interconnect but propagated along the intermetallic–substrate interface in the aged SnBi–Cu interconnect. While fracture of the intermetallic–substrate interface in SnBi–Cu interconnect was due to Bi segregation onto that interface, no Bi was detected at the intermetallic-substrate interface in SnBi–Ni interconnects, implying that Ni(P) was effective in inhibiting the interfacial segregation of Bi.

The transformation of second-phase particles in a Cu-Fe alloy following equal-channel angular extrusion and annealing has been determined by transmission electron microscopy. Equal-channel angular pressing of the Cu-Fe alloy transformed coherent gamma-Fe particles in the Cu matrix into incoherent alpha-Fe. Upon annealing, numerous coherent gamma-Fe particles were observed. A dislocation-particle interaction mechanism is suggested to explain the re-precipitation of coherent gamma-Fe particles following annealing.

Low-cycle fatigue behavior of the Sn-Ag-Cu ternary-eutectic alloy was investigated under a fully reversed loading condition. The solder alloy exhibited cyclic softening early in the fatigue life and continued to soften as the number of fatigue cycles increased. Following cyclic loading, numerous microcracks were found in the microstructure. Most of the microcracks were located along the grain boundaries in the areas with finer grains. The areal density of the microcracks increased with both strain amplitude and cycle number. By combining percolation theory with microcracking analysis, the cycle-dependent softening behavior was shown to result from accumulation of microcrack density with fatigue cycles.

Domain structures in a tetragonal ferroelectric crystal were examined by transmission electron microscopy (TEM) before and after application of bipolar cyclic electric fields. Prior to the application of the bipolar field, the crystal was poled to an initial domain structure which consisted of a high volume fraction of c domains. Dispersed in the matrix of the c domains were two orthogonal sets of a-domain strips. These two sets of a-domain strips stayed apart to avoid direct contact. Upon application of bipolar cyclic electric fields, intersections of the a domains were observed in the ⟨001⟩-oriented tetragonal ferroelectric crystal. These intersections were formed as one set of the a domains grew under the influence of the in-plane electric field. As a result of the domain wall intersection, segments of the domain wall between two intersecting a domains carried excess electric charges. In the successive TEM examination, domain wall distortion and microcracks were found at these intersections.

Domain behaviour under electric cycling was examined by transmission electron microscopy in a -oriented 0.65Pb(Mg 1/3 Nb 2/3 )O 3 -0.35PbTiO 3 ferroelectric crystal. Prior to electric cycling, the crystal contained two nonparallel sets of 90° domain walls along the two {110} planes. For the most part, the domain walls remained planar, dividing the crystal into highly regular domain strips. As two nonparallel domain walls approached each other, the domain width tapered down to avoid full contact. Upon repeated electric cycling, the domains were forced into full contact, resulting in direct intersections of 90° domain walls and charged wall segments along the domain intersection. At the domain intersection, partial dislocations were observed along with a stacking fault on a {101} plane. These dislocations had a Burgers vector of [101] and were of predominantly screw type. It is suggested that the partial dislocations resulted from a shear displacement along [101] in the crystal as the domain switched its polarization to form the intersection.

The field-driven in-situ transmission electron microscopy (TEM) technique was developed to examine micromechanisms of field-induced cracking in ferroelectric ceramics. The technique was constructed by combining a selectively deposited thin film electrode configuration with a modified hot stage to deliver a required electric voltage to a ferroelectric TEM specimen. Under cyclic electric fields, microcracks were found to initiate from pores at the triple junctions and propagate along the grain-boundary in a lead zirconate titanate (PZT) ceramic. Grain-boundary cavitation and coalescence of microcracks were directly observed for the first time during field-induced fracture of PZT at room temperature. The results suggest that dielectric breakdown of the grain-boundary phase was conducive to grain-boundary cavitation, and the crack growth followed the progressive accumulation of the cavity density with electric cycling.

A novel Cu2O/TiO2 composite photocatalyst structure of Cu2O nanospheres decorated with TiO2 nanoislands were synthesized by a facile hydrolyzation reaction followed by a solvent-thermal process. In this Cu2O/TiO2 composite photocatalyst, Cu2O served as the main visible light absorber, while TiO2 nanoislands formed heterojunctions of good contact with Cu2O, beneficial to the photoexcited electron transfer between them. Their band structure match and inner electrostatic field from the p-n heterojunction both favored the transfer of photoexcited electrons from Cu2O to TiO2, which effectively separated the electron-hole pairs. Photogenerated holes on Cu2O could react with water or organic pollutants/microorganisms in water to avoid accumulation on Cu2O because of the partial TiO2 nanoislands coverage, which enhanced their stability during the photocatalysis process. Their superior photocatalytic performance under visible light illumination was demonstrated in both the degradation of methyl orange and the disinfection of Escherichia coli bacteria. An interesting post-illumination catalytic memory was also observed for this composite photocatalyst as demonstrated in the disinfection of Escherichia coli bacteria in the dark after the visible light was shut off, which could be attributed to the transfer of photoexcited electrons from Cu2O to TiO2 and their trapping on TiO2 under visible light illumination, and their release in the dark after the visible light was shut off.

A new experimental technique for determining mechanical properties of polymer–metal interfaces was developed by replacing the conventional mechanical testing machine with a piezoelectric actuator. The actuator was made from a thin ferroelectric ceramic beam attached to a bilayer polymer-metal composite specimen. The trilayer specimen was loaded by applying ac electric fields on the piezoelectric actuator to drive crack growth along the polymer-metal interface. Subcritical crack growth was observed along the epoxy/aluminum interface, and the growth rate was found to depend on the magnitude of the applied electric field. The fracture mechanics driving force for the crack growth was computed from the finite element analysis as a function of crack length, applied field, material properties, and specimen geometry. Kinetics of the crack growth was correlated with the piezoelectric driving force.

Response of ferroelectric domains to mechanical stresses was studied on a oriented piezoelectric 0.65Pb(Mg 1/3 Nb 2/3 )O 3 –0.35PbTiO 3 (0.65PMN–0.35PT) crystal. Stress-induced domain switching was observed in the stress field of a microindentation and was confined to butterfly-shaped switching zones which extended preferentially along the directions. Based on a critical shear stress criterion, a stress analysis was made to determine the condition for the 90° domain switching. The analysis predicted a hyperbolic contour for the switching-zone boundary, in agreement with the experimental observations.

In situ transmission electron microscopy (TEM) technique was developed to examine micromechanisms of the electric fatigue in ferroelectric ceramics. The technique was based on a specially designed specimen connected to a modified TEM heating stage. With this technique, domain switching and nanodomain alignment near crack-like flaws were observed under cyclic electric fields. Following repeated electric cycles, microcracks were found to develop along domain and grain boundaries.