Lead-free solders with high Sn content cause excessive interfacial reactions at the interface with under-bump metallization during reflow. The interface formed after reflow affects the reliability of the solder joint. For this paper, we investigated the interfacial reactions of Sn0.7Cu and Sn36Pb2Ag solder on electrolytic Ni layer for different reflow times. The traditionally used Sn36Pb2Ag solder was used as a reference. It was found that during as-reflowed, the formation of Cu-rich Sn–Cu–Ni ternary intermetallic compounds (TIMCs) at the interface of Sn0.7Cu solder with electrolytic Ni is much quicker, resulting in the entrapment of some Pb (which is present as impurity in the Sn–Cu solder) rich phase in the TIMCs. During extended time of reflow, high (>30 at.%), medium (30-15 at.%) and low (<15 at.%) Cu TIMCs formed at the interface. The amount of Cu determined the growth rate of TIMCs. Cu-rich TIMCs had higher growth rate and consumed more Ni layer. By contrast, the growth rate of the Ni–Sn binary intermetallic compounds (BIMCs) in the Sn36Pb2Ag solder joint was slower, and the Ni–Sn BIMC was more stable and adherent. The dissolution rate of electrolytic Ni layer for Sn0.7Cu solder joint was higher than the Sn36Pb2Ag solder joints. Less than 3 μm of the electrolytic Ni layer was consumed during molten reaction by the higher Sn containing Sn0.7Cu solder in 180 min at 250 °C. The shear strength of Sn–Pb–Ag solder joints decreased within 30 min of reflow time from 1.938 to 1.579 kgf due to rapid formation of ternary Ni–Sn–Au compounds on the Ni–Sn BIMCs. The shear strength of Sn0.7Cu solder joint is relatively stable from 1.982 to 1.861 kgf during extended time reflow. Cu prevents the resettlement of Au at the interface. The shear strength does not depend on the thickness of intermetallic compounds (IMCs) and reflow time. Ni/Sn–Cu solder system has higher strength and can be used during prolonged reflow.

The hardness, elastic moduli, and fracture toughness of the spinel phases, γ–Ge3N4 and γ–Sn3N4, were determined using indentation data and theoretical calculations. Measurements were performed on polycrystalline specimens using the technique of nanoindentation to determine the reduced moduli and hardnesses from the unloading portion of the indent curves. Reduced moduli of γ–Ge3N4 and γ–Sn3N4 were found to be 295 and 167 GPa, respectively. The nanohardnesses of γ–Ge3N4 and γ–Sn3N4 were found to be 31 and 13 GPa, respectively. The shear moduli G0 and Poisson’s ratios ν0 were derived using theoretical bulk moduli B0 obtained from density-functional theory calculations. The calculated values were B0 = 260 GPa, G0 = 146 GPa, ν0 = 0.26 for γ–Ge3N4, and B0 = 186 GPa, G0 = 64 GPa, ν0 = 0.34 for γ–Sn3N4. Fracture toughness was estimated by direct measurement of radial cracks emanating from Vickers microindents. It was determined that for γ–Ge3N4, KIC = 2.3 MPa(m)1/2, while for γ–Sn3N4, KIC = 1.4 MPa(m).1/2

The growth of the polycyclic aromatic hydrocarbon perylene on (110) oriented copper substrates has been studied by means of x-ray photoelectron spectroscopy, near-edge x-ray absorption spectroscopy, and atomic force microscopy. In the monolayer regime, the molecules are orientated with their molecular plane parallel to the substrate, whereas they adopt a tilted arrangement in multilayer films. For multilayers with thicknesses exceeding 10 nm, the molecules grow in a bulk-like structure with their long axes orientated upright to the substrate surface.

Short carbon fiber (SCF) filled high-density polyethylene conductive composites were studied in terms of time-dependent piezoresistive behaviors. The time-dependent change of resistance under constant stress or strain was found to be the succession of the previous pressure-dependent piezoresistance. Depending on the filler volume fraction and the level of the constant stress or strain, resistance creep and resistance relaxation with different directions were observed. An empirical expression similar to the Burgers equation could be applied to fit the data for both the resistance creep and the resistance relaxation. The fitted relaxation time as a function of pressure showed that there exist two competing processes controlling the piezoresistive behavior and its time dependence. Mechanical creep and stress relaxation of the composites were also studied, and a comparison with the time-dependent resistance implied that there is a conducting percolation network attributed to the physical contacts between SCF and a mechanical network formed by the molecular entanglement or physical crosslinking of the polymer matrix and the interaction between the filler and the matrix. It is believed that the two networks dominate the electrical and the mechanical behaviors, respectively.

Bulk austenitic stainless steels (SS) have a face-centered cubic (fcc) structure. However, sputter deposited films synthesized using austenitic stainless steel targets usually exhibit body-centered cubic (bcc) structure or a mixture of fcc and bcc phases. This paper presents studies on the effect of processing parameters on the phase stability of 304 and 330 SS thin films. The 304 SS thin films with in-plane, biaxial residual stresses in the range of approximately 1 GPa (tensile) to approximately 300 MPa (compressive) exhibited only bcc structure. The retention of bcc 304 SS after high-temperature annealing followed by slow furnace cooling indicates depletion of Ni in as-sputtered 304 SS films. The 330 SS films sputtered at room temperature possess pure fcc phase. The Ni content and the substrate temperature during deposition are crucial factors in determining the phase stability in sputter deposited austenitic SS films.

In conventional continuum mechanics, the yield behavior of a material is size independent. However, in nanoindentation, plasticity size effects have been observed for many years, where a higher hardness is measured for smaller indentation size. In this paper we show that there was a size effect in the initiation of plasticity, by using spherical indenters with different radii, and that the length scale at which the size effect became significant depended on the mechanism of plastic deformation. For yield by densification (fused silica), there was no size effect in the nanoindentation regime. For phase transition (silicon), the length scale was of the order tens of nanometers. For materials that deform by dislocations (InGaAs/InP), the length scale was of the order a micrometer, to provide the space required for a dislocation to operate. We show that these size effects are the result of yield initiating over a finite volume and predict the length scale over which each mechanism should become significant.

The heteroepitaxial growth of GaSb thin films on Si(100) and GaAs(100) substrates is presented. The growth technique involves the use of atomic Ga and Sb species, which are provided by thermal effusion and radio frequency sputtering, respectively. The crystalline quality of the heteroepitaxial GaSb film on the Si substrate is high despite the larger lattice mismatch. Epitaxial quality is determined by high-resolution x-ray diffraction and Rutherford backscatter spectrometry channeling. Atomic-force microscopy is used to monitor the evolution of surface morphology with increasing film thickness. Transmission electron microscopy shows the formation of stacking faults at the Si/GaSb interface and their eventual annihilation with increasing GaSb film thickness. Annihilation of stacking faults occurs when two next-neighbor mounds meet during the overgrowth of a common adjacent mound.

Hydrothermal reaction of phosphomolybdic acid (PMo12) and phosphotungstic acid (PW12) with the surfactant template 1,10-decanediamine (1,10-DAD) yielded two new nanocomposites, [C10H20(NH2)2]2·H3PMo12O40·(H2O)7.5 and [C10H20(NH2)2]2·H3PW12O40·(H2O)2.4. The produced needlelike crystals of the two nanocomposites have fine-layered structures. X-ray diffraction analyses indicate that change of polyoxometallates has little effect on the tilt angle of the 1,10-DAD molecules for such polyoxometallates–organic amine systems. Fourier transform infrared and Raman spectra show that in the hybrid, the PMo12 forms infinite two-dimensional networks, and the PW12 keeps its Keggin structure in the hybrid except distortion to some degree. The two nanocomposites show different photochromic properties; PMo12–DAD hybrid can be colored under ultraviolet irradiation, whereas PW12–DAD hybrid cannot.

Al2O3–(m-ZrO2)/t-ZrO2 composite having fibrous and homogeneous microstructure was successfully fabricated using a fibrous monolithic process. The composites had a homogeneous microstructure as well as good interfaces between the Al2O3–(m-ZrO2) and t-ZrO2 phases. The thickness of each phases were reduced to 375, 50, 5 μm, and 0.7 μm as the number of extrusion passes increased up to 5. The material properties of density, hardness, bending strength, and fracture toughness increased as the passes of extrusion were increased up to a fifth pass, and their maximum values were about 98.5%, 1230 Hv, 570 MPa, and 6.5 MPa⋅m1/2, respectively. The fracture toughnesses in the direction of longitudinal and transverse direction of the fifth passed sample showed the different values with about 6.5 and 5.4 MPa⋅m1/2, respectively.

The interfacial reactions of Sn–Zn based solder on Cu and Cu/Ni–P/Cu–plating substrates under aging at 150 °C were investigated in this study. The compositions of solders investigated were Sn–9Zn, Sn–8.55Zn–0.45Al, and Sn–8.55Zn–0.45Al–0.5Ag solders in weight percent. The experimental results indicated that the Cu substrate formed Cu5Zn8 with the Sn–9Zn solder and Al–Cu–Zn compound with Al–containing solders. However, it was detected that Cu6Sn5 formed at the Sn–9Zn/Cu interface and Cu5Zn8 formed at the Al–containing solders/Cu interface after aging for 1000 h. When it contacted with the Cu/Ni–P/Au substrate, the Sn–9Zn solder formed Au–Zn compound, and the Al–containing solders formed Al–Cu–Zn compound at the interface. After a long aging time, the intermetallic compounds existing between solders and the Cu/Ni–P/Au metallization layers almost did not grow. It was found that the interdiffusion between solders and Cu/Ni–P/Au was slower than that with Cu under aging. Furthermore, the addition of Ag to Sn–Zn solder resulted in the formation of AgZn3 particles at the interface.

Mechanical properties and fracture characteristics of Zr-based bulk metallic glass (BMG) composites containing carbon nanotube (CNT) addition were investigated in detail. The interfacial reaction between the added CNTs and the glass matrix causes the formation of some V-shape nicks on the residual CNTs. These nicks have significant effect on the mechanical properties and fracture modes of the BMG composites. The compressive fracture strength increases with increasing the volume fraction of CNT addition at first, and starts to decrease gradually when the volume fraction of CNT addition is more than 5.0%. The fracture modes of the BMG composites also change from typical shear flow deformation behavior to completely embrittling fracture gradually. The V-shape nicks originating from the interfacial reaction are responsible for the decrease of fracture strength and the variation of fracture modes.

[Sm–Co (3x nm) /Co (x nm)]10 (x = 10, 7, 4) multilayered films have been prepared by magnetron rf-sputtering. It is found that the thickness of both hard and soft layers has important effects on phase transformation and magnetic interaction of films. With a fixed ratio of hard- to soft-layer thickness, decreasing simultaneously the thickness of these layers results in increasing coercivity. The effects of the external magnetic field during annealing depend on the Co-layer thickness (x value), mainly because of the formation of different main phases for different thickness of Co layer. For the films with x = 10 and 7, the main phase is Sm2Co17 after annealed. Applying a magnetic field during annealing promotes the crystallization of films, and therefore, it increases the coercivity of the films with x = 10 and 7. Magnetic interaction has been investigated by measuring δm and remanence magnetization. All the films show that although the exchange coupling favorable for magnetization is significant, the increase of the coercivity mainly originates from improving the pinning effects. Temperature dependence of the coercivity supports that the pinning of domain-walls constitutes a control mechanism of the coercivity. This behavior can be well understood in terms of the Gaunt’s approach of the coercivity.

In this paper, a new scheme has been proposed for the computational modeling of conical indentation in plastically graded materials. Based on the new scheme and the work of Dao et al. [Acta Mater.49, 3899 (2001)], and taking the example of conical indentation with an indenter whose tip apex angle is θ = 70.3°, an analytical expression to predict the loading P - h curve for the indentation of plastically graded materials has been presented. A reverse algorithm has further been established to determine the plastic properties of a plastically graded surface. The existence, uniqueness, and stability of the solution to the inverse problem have been systematically investigated. The current work can be applied to the evaluation or optimization of various plastically graded surfaces.

Silver nanoparticles dispersed in a silica matrix were made by the consolidation of a Ag-attached silica colloid, which was synthesized via the electrolysis of a pure Ag electrode, the reduction of Ag+ ions by H2, and the nucleation and growth of Ag particles on the silica nanoparticles in water. This simple process produced Ag/silica nanocomposites with a high concentration and narrow size distribution of nanoparticles, which was confirmed by transmission electron microscopy and x-ray diffraction. As estimated by Raman and photoluminescence measurements, the quantity of broken oxygen bonds was increased with increasing Ag concentration due to the intervention of Ag ions as structural modifiers in the silica network structure. Ag ions in the matrix are probably a residue of the Ag+ ions that could not be reduced by H2 during the electrolysis/reduction reaction. The optical-absorption spectra and the HCl-soaking test suggested that a chemical-interface damping effect, which was caused by electron transfer from the metal particles to the oxide matrix, dominates the optical-absorption properties in this system.

Although crystalline silicon is not generally considered susceptible to fatigue crack growth, recent studies suggest that there may be fatigue processes in silicon micro-machined structures. In the present study, a micro-machined fracture specimen geometry was used to examine stable crack growth under fatigue loading. Crack length and loads were carefully monitored throughout the test to distinguish between environmentally assisted crack growth (stress corrosion) and mechanically induced fatigue-crack growth. Results revealed similar steplike crack extension versus time for the cyclic and monotonic tests. The fatigue crack-growth curve extracted from the crack extension data exhibited a nearly vertical slope with no evidence of accelerated crack-growth rates. Fracture surfaces for the monotonic and cyclic tests were similar, further suggesting that a true mechanical fatigue crack-growth mechanism did not occur. Explanations for the observed lack of fatigue crack growth are presented and discussed with respect to reported stress-life behavior.

Nanoparticles of barium orthotitanate (Ba2TiO4) was obtained using microemulsions (avoiding Ba-alkoxide). Powder x-ray diffraction studies of the powder after calcining at 800 °C resulted in a mixture of orthorhombic (70%) and monoclinic (30%) phases. The high-temperature orthorhombic form present at 800 °C was due to the small size of particles obtained by the reverse micellar route. Pure orthorhombic Ba2TiO4 was obtained on further sintering at 1000 °C with lattice parameters a = 6.101(2) Å, b =22.94(1) Å, c = 10.533(2) Å (space group, P21nb). The particle size obtained from x-ray line broadening studies and transmission electron microscopic studies was found to be 40–50 nm for the powder obtained after heating at 800 °C. Sintering at 1000 °C showed increase in grain size up to 150 nm. Our studies corroborate well with the presence of a martensitic transition in Ba2TiO4. The dielectric constant was found to be 40 for Ba2TiO4 (at 100 kHz) for samples sintered at 1000 °C. The dielectric loss obtained was low (0.06) at 100 kHz.

The effect of process conditions on the biaxial texture of MgO films grown by ion-beam-assisted deposition (IBAD) was studied. The texture showed a strong dependence on the Ar+/MgO flux ratio, but a weak dependence on the divergence of Ar+ beam. One hundred-nanometer-thick epi-MgO on less than 10-nm-thick textured IBAD-MgO films that were grown on 7-nm-thick Y2O3 layers on fused silica, metal alloy tape, and polished Si substrates showed biaxial texture with in- and out-of-plane orientation distributions of less than 4° and 2°, respectively. These results strengthen the notion that the IBAD technique could serve as a universal technological process to integrate amorphous and polycrystalline substrates with various oxide and semiconductor films that need to be grown with good biaxial texture.

Nanocrystal-(Ti,Al)xN1-x/amorphous-SiyN1-y nanolaminate films were deposited periodically under different nitrogen flow rates. The composition, microstructure and mechanical properties of nanolaminate films were investigated by x-ray photoelectron spectroscope, x-ray diffractometer, scanning and transmission electron microscopy, atomic force microscope, and nanoindentation apparatus. Results indicated that the formation of the compound on the target surface was substantially influenced by the deposition rate, composition and crystallite size of the nanolaminate films. Nanolaminate structure with periodic compositional modulation and sharp interfaces were deposited at different nitrogen flow rate. Smaller nanocrystallite size, round-shaped grain features, smoother surface morphology, higher hardness, and reduced elastic modulus were obtained for nanolaminate films with increasing the nitrogen flow rate.

The effects of different particle size distributions on the real-time hydration of tricalcium silicate cement paste were studied in situ by quasi-elastic neutron scattering. The changing state of water in the cement system was followed as a function both of cement hydration time and of temperature for different initial particle size distributions. It was found that the length of the initial, dormant, induction period, together with the kinetics of hydration product nucleation and growth, depends on the hydration temperature but not on the particle size distribution. However, initial particle size does affect the total amount of cement hydrated, with finer particle size producing more hydrated cement. Furthermore, the diffusion-limited rate of hydration at later hydration time is largely determined by the initial tricalcium silicate particle size distribution.

Particulate composites of magnetostrictive Terfenol-D were prepared with polyamine and anhydride cured epoxy polymer matrices with the presence or the absence of a strong magnetic field. These composites were studied to investigate (i) the influence of magnetic field that is applied during specimen preparation in strain output levels, (ii) performance loss at high temperatures, and (iii) the influence of matrix material in magnetostrictive strain performance. A six-way comparison is made of materials processed under magnetic field with materials processed under no magnetic field, and magnetostrictive strain performance at glass transition finish temperature with magnetostrictive strain performance at glass transition start temperature, and magnetostrictive strain performance in low modulus matrix systems with magnetostrictive strain performance in high modulus matrix systems. A four-way comparison is also made between the micrographs for strain-cycled and non-strain-cycled samples and relative damage incurred by samples prepared using high and low modulus matrix systems.