An analysis of size effects and doping on the strength of ultrananocrystalline diamond (UNCD) thin films is presented. The doping was achieved by the addition of nitrogen gas to the Ar/CH4 microwave plasma. The strength data, obtained by means of the membrane deflection experiment (MDE) were interpreted using Weibull statistics. The validity and predictive capability of the theory were examined in conjunction with detailed fractographic and transmission electron microscopy microstructural analysis. The Weibull parameters were estimated nonlinear regression based on 480 tests when the specimen volume varied from 500 to 16,000 μm3. Both undoped and doped UNCD films exhibited a decrease in strength with an increase in specimen size. A significant drop in strength was measured when the films were doped with nitrogen. Such a drop was almost independent of the percentage of doping. The results also showed that one can predict the fracture strength of a component possessing any arbitrary volume to within ±3%. Moreover, the failure mode of UNCD was found to be volume controlled. We also report changes in Young’s modulus as a function of doping for n-doped UNCD thin films.

Single crystals of the multiferroic (1 − x)BiFeO3–xPbTiO3 (BF–PT) solid solution with a nominal morphotropic phase boundary (MPB) composition were grown from flux. Structural characterization by x-ray diffraction shows the simultaneous existence of a tetragonal, an orthorhombic, and a rhombohedral perovskite phase in the crystals. A high ferroelectric Curie point of 660 °C was found in the BF–PT crystals by dielectric measurements. The variation of the magnetic moment as a function of temperature of the BF–PT crystals measured under zero field cooling mode reveals three anomalies with the highest one around 440 K, corresponding to the antiferromagnetic ordering temperatures of the rhombohedral, orthorhombic, and tetragonal phases, respectively. These results demonstrate the intrinsic relations between the MPB phase components and the macroscopic ferroic properties.

Multilayer thin-film materials with various thicknesses, compositions, and deposition methods for each layer typically exhibit residual stresses. In situ transmission electron microscopy (TEM) is a powerful technique that has been used to determine correlations between residual stresses and the microstructure. However, to produce electron transparent specimens for TEM, one or more layers of the film are sacrificed, thus altering the state of stresses. By conducting a stress analysis of multilayer thin-film TEM specimens, using a finite element method, we show that the film stresses can be considerably altered after TEM sample preparation. The stress state depends on the geometry and the interactions among multiple layers.

We demonstrate the aqueous self-assembly of ligand-assisted SnO2 sol precursors onto preformed poly-l-lysine templates through interfacial electrostatic forces (COO−/NH3+). On the removal of organics, two unique coral-like and sea worm-like textures consisting of hierarchical pores (macropores and mesopores) and nanocrystalline SnO2 frameworks are synthesized, mainly depending on the chelator/Sn molar ratio. Structural formation is discussed based on acid-base interaction and interfacial charge density matching. For the first time, metal oxide structures mediated by polypeptides are reported. More importantly, the method described here might open a generally attractive route for synthesizing complex nanostructures of other oxides (e.g., ZnO, TiO2, and ZrO2).

Al2O3 films are grown by atomic layer deposition (ALD) using trimethylaluminum and water as precursors on HF-last and NH3 plasma pretreatment Si substrates. The thickness, surface roughness, and density of Al2O3 films as well as the nature of their interlayers with Si substrates are characterized by x-ray reflectivity and spectroscopic ellipsometry techniques. The growth rates of Al2O3 films are 1.1 Å/cycle and 1.3 Å/cycle, respectively, on HF-last and NH3-plasma-nitrided surfaces. Al2O3 layer densities are rather independent of the number of growth cycles in all cases. The interfacial film thickness increases with the number of ALD cycles when deposited on an HF-last Si substrate. However, because SiOxNy inhibits oxygen diffusion, the interfacial film thickness is independent of the number of ALD cycles on the nitrided Si substrate.

Sn–8Zn–3Bi solder paste and Sn–3.2Ag–0.5Cu solder balls were reflowed simultaneously at 240 °C on Cu/Ni/Au metallized ball grid array substrates. The joints without Sn–Zn–Bi addition (only Sn–Ag–Cu) were studied as a control system. Electrical resistance was measured after multiple reflows and aging. The electrical resistance of the joint (R1) consisted of three parts: the solder bulk (Rsolder bulk, upper solder highly beyond the mask), interfacial solder/intermetallic compound (Rsolder/IMC), and the substrate (Rsubstrate). R1 increased with reflows and aging time. Rsolder/IMC, rather than Rsolder bulk and Rsubstrate, seemed to increase with reflows and aging time. The increase of R1 was ascribed to the Rsolder/IMC rises. Rsubstrate was the major contribution to R1. However Rsolder/IMC dominated the increase of R1 with reflows and aging. R1 of Sn–Zn–Bi/Sn–Ag–Cu samples were higher than that of Sn–Ag–Cu samples in various tests.

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

The nature of the elastic unloading after an elastic-plastic contact with a conical or Berkovich indenter is studied. Three representative specimens having different mechanical properties were tested. Finite-element results for the pressure distribution beneath the indenter during unloading suggest that the effective indenter is in fact very closely approximated by a sphere in the case of fused silica (a material with a relatively low value of E/H) and a more uniform pressure distribution in the case of silicon and sapphire (materials with higher values of E/H). The proposed reason for these observations is the extent and influence of an elastic enclave directly beneath the indenter as revealed by finite-element analysis. The results also show that the pressure distribution retains its form during the entire unloading. The work seeks to provide a physical reason for the value of the fitting exponent m as used in popular nanoindentation data analysis procedures.

Using an infrared camera, the plastic deformation of a relaxed Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 bulk-metallic glass in a moderately high strain rate compression was observed in situ. The specimen exhibits an inhomogeneous deformation, which is manifested by serrated plastic flow, shear banding, and obvious work softening. Shear-banding operations were observed throughout the plastic deformation. Shear-banding operations started before the nominal yielding; shear bands could not block each other, but their interaction seems to accelerate the plastic deformation. A significant increase in the specimen’s temperature was observed due to shear banding.

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

Finite element analysis is used to simulate indentation creep experiments with a cone-shaped indenter. The purpose of the work is to help identify the relationship between the strain-rate sensitivity of the hardness, νH, and that of the flow stress, νσ in materials for which elastic deformations are significant. In general, νH differs from νσ, but the ratio νH/νσ is found to be a unique function of H/E* where H is the hardness and E* is the modulus relevant to Hertzian contact. νH/νσ approaches 1 for small H/E*, 0 for large H/E*, and is insensitive to work hardening. The trend in νH/νσ as a function of H/E* can be explained based on a generalized analysis of Tabor’s relation in which hardness is proportional to the flow stress H = k × σeff and in which the proportionality factor k is a function of σeff/E*.

Multiferroic magnetoelectrics are materials that are both ferroelectric and ferromagnetic in the same phase. In addition, electric and magnetic polarizations are strongly coupled in some magnetoelectric multiferroic materials. In this work, by virtue of the image method, exact closed-form Green’s functions are derived for a uniaxial multiferroic full-space, half-space, and bimaterial space. While for the bimaterial space case the interface is assumed to be perfect, for the half-space case four different sets of surface conditions are considered. The point source can be either an electric or a magnetic charge. Numerical results are presented to demonstrate the differences among the infinite-space, half-space, and bimaterial space Green’s functions.

Varying amounts of Zn (1, 3, and 7 wt%) were added to Sn–3.5Ag solder on a Cu pad, and the resultant solder joint microstructures after a reflow and isothermal aging (150 °C, up to 500 h) were investigated using scanning electron microscopy, energy dispersive x-ray, and x-ray diffraction, which were subsequently correlated to the results of microhardness and drop tests. Zinc was effective in improving the drop resistance of Sn–3.5Ag solder on the Cu pad, and an addition of 3 wt% Zn nearly doubled the number of drops-to-failure (Nf). The beneficial role of Zn was ascribed to suppression of Cu6Sn5 and precipitation of Zn-containing intermetallic compounds (IMCs). However, the Zn effect was reduced as Cu6Sn5 and Ag3Sn precipitated in a joint IMC layer after prolonged aging. The interface between Ag5Zn8 and Cu5Zn8 was resistant to drop impact, but two other layered IMC structures of Cu6Sn5/Cu3Sn and Cu5Zn8/Cu6Sn5 were not.

This paper presents the design, fabrication, and mechanical testing of a bioinspired composite structure with characteristic dimensions on the order of tens of microns. The microarchitecture, designed and fabricated using microelectromechanical systems (MEMS) technology, involves two distinct length scales and represents the first attempt at mimicking the crossed-lamellar microstructure of molluscan shells such as the giant Queen conch, Strombus gigas, which contains features with dimensions spanning five distinct length scales. The displacement control capabilities of a nanoindenter enabled the observation of the graceful failure of the micro-composite under three point bending and, in turn, the measurement of its post-peak load–displacement response and work of fracture.

We present evidence that a minor adjustment in Zr/Ni concentration ratio can dramatically enhance the plasticity of monolithic Zr-based bulk metallic glasses (BMGs) from about 2.2% for Zr65Al8Ni10Cu17 BMG to 14% for Zr62Al8Ni13Cu17 BMG. No deformation-induced nanocrystallization appears in a 55% strained Zr62Al8Ni13Cu17 BMG without catastrophic failure while pre-existing nanocrystals in Zr65Al8Ni10Cu17 BMG result in its limited plasticity. Also note that the stability of Zr62Al8Ni13Cu17 BMG against crystallization upon deformation is somewhat higher than that of Zr65Al8Ni10Cu17 BMG. As determined by x-ray diffraction using synchrotron radiation, the enhanced plasticity of Zr62Al8Ni13Cu17 BMG seems to be related to the relative homogeneity of the amorphous structure.

Unlike the dislocation-based plasticity in crystalline metals, which can be readily explained by their crystal structure and the presence of defects, the nature of the plasticity in amorphous alloys is not completely understood. Experiments have shown that the plasticity in amorphous alloys is strongly dependent on their atomic packing density. This study, based on the combination of experimental and computational techniques, examines the origin of the plasticity in amorphous alloys considering characteristics of the inherent atomic-scale structure as defined by short-range ordered (SRO) clusters. The role of various SRO atomic clusters in creating free volume during shear deformation is discussed. We report that the plasticity exhibited by amorphous alloys is very sensitive to the characteristics of the atomic packing state, which can be described by various SRO atomic structures and quantified by the effective activation energy for crystallization.

The influence of the Ti/Ba ratio on the formation of pyroelectric and piezoelectric quasi-amorphous BaTiO3 films was investigated. Three types of films, Ti-rich, Ba-rich, and stoichiometric, were pulled through a temperature gradient or subjected to isothermal heating. The quasi-amorphous polar phase only formed in films pulled through the temperature gradient with Ti/Ba ratio within the broad range of 0.95–1.1. This implies that quasi-amorphous pyroelectric and piezoelectric thin films are significantly more tolerant of a deviation from stoichiometry than their crystalline counterparts.

We present a systematic study of homogeneous deformation in a La-based bulk metallic glass and two in situ composites based on the same glass. In contrast to prior investigations, which focused on relatively dilute composites, in this work the reinforcement volume percentages were more concentrated at 37% and 52%—near or above the percolation threshold (35–40%). Hot uniaxial compressive testing was conducted over a wide strain rate range from 10−2to 10−5s−1at a temperature near the glass transition. For such concentrated composites, the homogeneous deformation behavior appeared to be dominated by the properties of the reinforcement phase; in the present case the La reinforcements deformed by glide-controlled creep. Post-deformation analysis suggested that bulk metallic glass matrix composites were susceptible to microstructural evolution, which appeared to be enhanced by deformation, in contrast with a stress-free anneal. Consequently, unreinforced bulk metallic glass appeared to be more structurally stable than its composites during deformation near the glass transition.

In this study, we fabricated eutectic Au–Sn (Au–20 wt% Sn) flip-chip solder bumps from a single electroplating bath. After reflowing, the average diameter of the solder bump was approximately 80 μm. The (Ni,Au)3Sn2 phase was initially formed when the liquid Au–Sn solder reacted with the Ni UBM (under bump metallization). After aging at 150 °C, the (Ni,Au)3Sn2 intermetallic compound (IMC), which formed at the interface during reflow, was fully transformed into the (Au,Ni)Sn IMC due to the restricted supply of Ni atoms from the UBM to the interface. On the other hand, after aging at 250 °C for 1000 h, two IMC layers, (Au,Ni)Sn and (Ni,Au)3Sn2, were formed at the interface. The lower (Ni,Au)3Sn2 phase was formed when the (Au,Ni)Sn phase reacted with the Ni UBM. The interfacial (Au,Ni)Sn IMC grew with the preferential consumption of the available δ-phase in the solder matrix. Eventually, the ζ-phase covered most of the interfacial layer. In the bump shear tests, the Au–Sn/Ni joint aged at 150 °C fractured through the bulk of the solder, confirming the mechanical reliability of the interface. In contrast, the Au–Sn/Ni joint aged at 250 °C fractured along the interface, thereby demonstrating brittle failure, possibly a result of the brittle IMC layer at the interface.

The dielectric and magnetic properties were investigated in Ta-substituted BiFeO3 polycrystalline ceramics synthesized by a solid-state reaction. The Ta substitution decreased the grain size by two orders of magnitude compared with that of unsubstituted ceramics and increased the electrical resistivity by 6 orders of magnitude. The high resistivity and low dielectric loss allowed the dielectric constant to be determined at room temperature. The magnetic hysteresis loops were observed in the Ta-substituted BiFeO3, and the appearance of ferromagnetism was closely associated with the distortion of the oxygen octahedra by the Ta substitution. The coupling between the electric and magnetic dipoles was examined by determining the changes of the dielectric constant with the external magnetic field.