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.

The anisotropic atomic structure in a Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glass strained during uniaxial tensile creep at 598 K was studied at room temperature using high-energy x-ray diffraction. Changes in the atomic structure were examined by comparing the total scattering function [S(Q)] and the reduced pair distribution function [G(r)] of the creep to that of a companion specimen subjected to the same heat treatment only. Two-dimensional maps of the ΔS(Q) and its Fourier transformation demonstrate the distribution in the bond orientation anisotropy increases with increasing total strain. A fit of the reduced pair distribution function using a simplified two-component model suggests that the bond length changes in the deformed creep samples are not uniform.

The magnetic phase diagrams of RMnO3 (R = Er, Yb, Tm, Ho) are investigated up to 14 T via magnetic and dielectric measurements. The stability range of the atomic force microscopy order below the Néel temperature of the studied RMnO3 extends to far higher magnetic fields than previously assumed. Magnetic irreversibility indicating the presence of a spontaneous magnetic moment is found near 50 K for R = Er, Yb, and Tm. At very low temperatures and low magnetic fields, the phase boundary defined by the ordering of the rare-earth moments is resolved. The sizable dielectric anomalies observed along all phase boundaries are evidence for strong spin-lattice coupling in the hexagonal RMnO3. In HoMnO3, the strong magnetoelastic distortions are investigated in more detail via magnetostriction experiments up to 14 T. The results are discussed based on existing data on magnetic symmetries and the interactions among the Mn-spins, the rare-earth moments, and the lattice.

The interaction of a gliding screw dislocation with stacking fault tetrahedron (SFT) in face-centered cubic (fcc) copper (Cu) was studied using molecular dynamics simulations. Upon intersection, the screw dislocation spontaneously cross slips on the SFT face. One of the cross-slipped Shockley partials glides toward the SFT base, partially absorbing the SFT. At low applied stress, partial absorption produces a superjog, with detachment of the trailing Shockley partial via an Orowan process. This leaves a small perfect SFT and a truncated base behind, which subsequently form a sheared SFT with a pair of opposite sense ledges. At higher applied shear stress, the ledges can self-heal by gliding toward an SFT apex and transform the sheared SFT into a perfect SFT. However, complete absorption or collapse of an SFT (or sheared SFT) by a moving screw dislocation is not observed. These observations provide insights into defect-free channel formation in deformed irradiated Cu.

In this work, formation of diamond coating is studied using large-scale molecular dynamics (MD) simulation. The diamond coating is studied to explore how and to what extent the temperature and pressure affects the deposition structure. To analyze the coating results, the radial distribution function and the fraction of diamond (sp3 bonds) is calculated. It is found that the sp3 fraction in the deposition structure increases with the temperature and pressure. When the pressure becomes large enough (10 GPa), the effect of the pressure on the coating structure is quite small and the sp3 fraction tends to be constant.

Damage behavior of Cu–Ta bilayered films bonded to polyimide (PI) substrates has been investigated by cyclic loading tests. Experimental results show that fatigue cracks preferentially initiated in the Ta layer close to the Ta–PI interface and propagated into the Cu layer perpendicular to the interface. The alignment of nanometer-sized Cu grains resulted from the potential GB sliding combined with a small amount of grain rotation was found in the damage zone ahead of the crack tip, and that is suggested to be a likely damage mechanism to accommodate cyclic plastic strain ahead of the fatigue crack tip of the submicrometer-thick Cu layer.

In ferrite–piezoelectric bilayers, the magnetoelectric (ME) interaction is mediated by mechanical strain. The ME coupling is expected to be strong, particularly when the magnetic and electric subsystems show resonance. Here we address the effect of magnetic exchange interactions on ME coupling at magnetoacoustic resonance (MAR), i.e., at the coincidence of electromechanical resonance in the piezoelectric phase and ferromagnetic resonance in a tangentially magnetized ferrite. When exchange is ignored, the estimated ME coefficient versus frequency profile shows a giant magnetoelectric coefficient at MAR, about 75–100 V/cm Oe for yttrium–iron garnet (YIG)/lead zirconate–titanate (PZT) nano bilayers. The magnetic exchange is predicted to enhance the coupling at MAR and produce a secondary peak due to the excitation of magnetoacoustic modes. Estimates of the ME coefficient are provided as a function of thickness ratio of YIG and PZT.

The objective of this study was to determine the geometric characteristics associated with the critical crack caused by cyclic loading. In an attempt to simulate an intraoral loading condition, the Hertzian cyclic loading of baria–silicate glass was performed using a type 302 stainless steel indenter under an aqueous environment using clinically relevant parameters, i.e., a low loading frequency (∼3 Hz) and a low load level (⩽200 N). The indenter diameter (4.76 mm) approximated the cuspal radii of molar and premolar teeth. Ten bar specimens each were subjected to loading cycles of 0, 103, 104, and 105 cycles. A four-point bending test was used to quantify the severity of the strength reduction caused by the repeated loading test. There was a decrease in fracture stress after 103 cycles that was associated with cone crack formation. No significant additional reduction was found after 105 cycles for specimens tested both in air and in deionized water. Stress-corrosion fatigue accelerated the surface crack propagation rate in baria–silicate glass specimens. Four different crack geometries were identified along with failure mechanisms. Various fracture mechanics approaches were tested against observed crack geometries. The previously unobserved triangular crack geometry was found.

This study investigated the electromigration behavior between Cu and Sn–9Zn solder under a current density of 1.0 × 103 A/cm2 for up to 230 h. The experimental results indicated that Cu5Zn8 was formed at the interface between Cu and the cathode side of the Sn–9Zn solder as well as in the bulk near the anode. Consumption of Cu was also observed for the Cu plating on the cathode side and anodic side, but with less compound formation and Cu consumption at the anode. The intermetallic compound layer on the cathode side was always thicker than that on the anode side after the same current-stressing time. The effect of chemical potential overwhelms electromigration in inducing Zn diffusion when a counterflow of electrons and chemical potential gradient exists. Voids formed at the Cu5Zn8–solder interface inside the solder regardless of the direction of current flow.

High strain-rate compression experiments were performed with a split-Hopkinson pressure bar (SHPB) at 500–4000/s on cylindrical samples of a Zr-based bulk metallic glass (LM-1) in both the fully amorphous and annealed conditions. The effects of changes to the specimen geometry (i.e., L/D ratio) and the material heat treatment [i.e., annealing versus amorphous (as-received)], on the peak stress, strain-to-failure, and failure behavior were determined with the aid of an in situ video obtained by using a high-speed digital camera in conjunction with the split-Hopkinson pressure bar (SHPB). Examination of the in situ video recordings and light optical microscopy showed that the failed samples revealed preferential failure initiating at the sample ends due to stress concentration at the sample-insert interface. A new insert design was developed using transient, elastic-plastic finite-element simulations to reduce the effects of these stress concentrations. SHPB testing, combined with in situ video, subsequently revealed that this new experimental configuration promoted failure within the gage length and away from the sample ends in the samples tested. Significant effects of specimen geometry, insert design, and annealing on the apparent values of the peak stress, strain-to-failure, and fracture behavior were exhibited.

Electromigration (EM) in Cu dual-damascene interconnects with extensions (also described as overhangs or reservoirs) ranging from 0 to 120 nm in the upper metal (M2) was investigated by an analytical model considering the work of electron wind and surface/interface energy. It was found that there exists a critical extension length beyond which increasing extension lengths ceases to prolong electromigration lifetimes. The critical extension length is a function of void size and electrical field gradient. The analytical model agrees very well with existing experimental results. Some design guidelines for electromigration-resistant circuits could be generated by the model.

The facet and dislocation structure of 5° and 7° [001]-tilt grain boundaries of YBa2Cu3O7−δ (YBCO) and Y0.7Ca0.3Ba2Cu3O7−δ (YCaBCO) thin film bicrystals were studied. A 24° [001]-tilt YBCO grain boundary was also examined to contrast with the low angle grain boundary faceting behavior. All the low-angle grain boundaries exhibit strong faceting along (100)/(010) and (110) and possess both straight symmetric segments containing equally spaced [100] unit dislocations and step asymmetric segments composed of (110) and (100)/(010) facets. Grain boundaries with a higher degree of meander acquired up to 40% (110) facets. The atomic structure of (110) facets was revealed by the atomic resolution Z-contrast imaging. The (110) facets are dissociated for both the YBCO and YCaBCO grain boundaries. We also found the Ca-doped (110) facets to be more extended along the grain boundary plane, consistent with our earlier finding of a dissociated dislocation core in Ca-doped (100) facets. These 5° and 7° misorientations that we studied are just in the range at which YBCO grain boundaries start to become obstacles to current flow. The above results will be helpful for understanding the current transport across YBCO low-angle grain boundaries.

Small-angle scattering (SAS) and ultra small-angle scattering techniques, employing x-rays and neutrons, were used to characterize six different aluminum nanopowders and nanopowders composed of molybdenum trioxide and tungsten trioxide nanoparticles. Each material has different primary particle morphology and aggregate and agglomerate geometry, and each is important to the development of nano-energetic materials. The combination of small-angle and ultra small-angle techniques allowed a wide range of length scales to be probed, providing a more complete characterization of the materials. For the aluminum-based materials, differences in the scattering of x-rays and neutrons from aluminum and aluminum oxide provided sensitivity to the metal core and metal oxide shell structure of the primary nanoparticles. Small-angle scattering was able to discriminate between particle size and shape and agglomerate and aggregate geometry, allowing analysis of both aspects of the structure. Using the results of these analyses and guided by scanning electron microscopy (SEM) images, physical models were developed, allowing for a quantitative determination of particle morphology, mean nanoparticle size, nanoparticle size distribution, surface layer thickness, and aggregate and agglomerate fractal dimension. Particle size distributions calculated using a maximum entropy algorithm or by assuming a log-normal particle size distribution function were comparable. Surface area and density determinations from the small-angle scattering measurements were comparable to those obtained from other, more commonly used analytical techniques: gas sorption using Brunauer–Emmett–Teller analysis, thermogravimetric analysis, and helium pycnometry. Particle size distribution functions derived from the SAS measurements agreed well with those obtained from SEM.

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.

We studied the effects of anisotropic pores and fiber texture on the fatigue strength and fracture surface of lotus-type porous magnesium fabricated through unidirectional solidification in pressurized hydrogen and argon atmospheres. The fatigue strength in the direction parallel to the longitudinal axis of pores is higher than that in the perpendicular direction. Not only anisotropic pores but also fiber texture grown along the pore direction contributes to the anisotropy in the fatigue strength. The fatigue strength at finite life of lotus magnesium is closely related to the ultimate tensile strength; the fatigue strength is proportional to the ultimate tensile strength for both loadings parallel and perpendicular to the pore direction. The fracture surface of lotus magnesium is not flat, which originates from porous structure. For parallel loading, fiber texture in lotus magnesium also contributes to the irregular surface, i.e., a combination of texture and pore structure affects fracture surfaces.

The indentation behavior of polycrystalline copper at room temperature was investigated with a flat cylindrical indenter applied to fatigue-peak overloading. The experimental results showed that fatigue-peak overloading can retard the indentation depth (d) propagation rate. After the period of overloading, the dpropagation rate arrived at a new steady-state value again. The greater the amplitude of the peak overloading, the more the number of cycles that were needed to remove the effect of overloading. The observations of indentation cross-sectional microstructures revealed that the mechanism of dpropagation was the nucleation, formation, and propagation of cracks around the indentation. The experimental results and their interpretation implied that there were some similarities between the indentation fatigue-depth propagation and the conventional fatigue-crack propagation under fatigue-peak overloading.

MIn(WO4)2 (M = Li, Na, and K) with InO6 and WO6 octahedra were synthesized via a conventional solid-state reaction method. The photophysical and photocatalytic properties were studied. Compared with WO3, which is unable to evolve H2 from an aqueous CH3OH solution under illumination, the three materials can evolve H2 and O2 from aqueous solutions with CH3OH and AgNO3 sacrificial reagents, respectively. The activity order of photocatalytic H2 evolution is NaIn(WO4)2 > LiIn(WO4)2 > KIn(WO4)2 under irradiation (λ > 200 nm). Under irradiation (λ > 300 nm), however, LiIn(WO4)2 has a high activity for photocatalytic H2 evolution over NaIn(WO4)2. It is also noteworthy that LiIn(WO4)2 and NaIn(WO4)2 exhibit the ability to split pure water. The results suggest that the bottoms of the conduction bands in these photocatalysts are raised to meet the potential requirements of photocatalytic H2 evolution.

Results are presented on the shock response of a zirconium-based bulk metallic glass (BMG), Zr41.25Ti13.75Ni10Cu12.5Be22.5, subjected to planar impact loading. An 82.5-mm bore single-stage gas-gun facility at Case Western Reserve University, Cleveland, OH, was used to conduct the shock experiments. The particle velocity profiles, measured at the back (free) surface of the target plate by using the velocity interferometer system for any reflector (VISAR), were analyzed to (i) better understand the structure of shock waves in BMG subjected to planar shock compression, (ii) estimate residual spall strength of the BMG after different levels of shock compression, and (iii) obtain the Hugoniot elastic limit (HEL) of the material. The spall strength was found to decrease moderately with increasing levels of the applied normal impact stress. The spall strength at a shock-induced stress of 4.4 GPa was 3.5 GPa while the spall strengths at shock-induced stresses of 5.1, 6.0, and 7.0 GPa were 2.72, 2.35, and 2.33 GPa, respectively. The HEL was estimated to be 6.15 GPa.

The dielectric response of La- and Dy- doped BiFeO3 thin films at microwave frequencies (up to 12 GHz) has been monitored as a function of frequency, direct current (dc) electric field, and magnetic field in a temperature range from 25 to 300 °C. Both the real and imaginary parts of the response have been found to be non-monotonic (oscillating) functions of measuring frequency. These oscillations are not particularly sensitive to a dc electric field; however, they are substantially dampened by a magnetic field. The same effect has been observed when the volume of the characterized sample is increased. This phenomenon is attributed to the presence of a limited number of structural features with a resonance type response. The exact origin of these features is unknown at present. Leakage current investigations were performed on the whole set of films. The films were highly resistive with low leakage current, thereby giving us confidence in the microwave measurements. These typically revealed ‘N’-type I-V characteristics.

Strontium barium niobate (Sr2.5Ba2.5Nb10O30) thin films were deposited on (001) SrTiO3 single-crystalline substrates by pulsed laser deposition. The growth nature was investigated by transmission electron microscopy (TEM). Selected-area electron diffraction and high-resolution transmission electron microscopy revealed the existence of six types of grains. These grains grew on the substrate in a partially epitaxial fashion. Geometrical models were built, which were confirmed by TEM observations. Based on the TEM results and geometrical analysis, a crystallographic model was developed. The strain nature resulting from the growth columns is discussed in this report.