Metallic multilayers of Cu/Al/Ti composition were studied by transmission electron microscopy (TEM) and plasmon energy-loss mapping as prototypes of nanoscale reactive multilayer systems with exothermic alloy formation in oxygen-free conditions. The selection and arrangement of alloy phases by the system during ex situ and in situ heating experiments were found to depend not only on temperature but strongly on the initial volume ratios of metals, and to a lesser degree on the dimensionality of the reactive sample. Here, a two-dimensional sample was represented by ex situ heating of the full multilayer structure, a one-dimensional sample refers to in situ heating of thin cross-sectional TEM specimens, while a zero-dimensional sample (or metallic dot-array) was obtained after cutting thin pillars using focused ion beams. Lamellar self-organized alternation between Heusler phase and Cu9Al4 was found.

In situ microlevel spherical B2 CuZr phase reinforced Zr49.5Cu36.45Ni4.05Al9Nb1 bulk metallic glass matrix composite was prepared successfully by the copper mold casting method. It was found that mechanical properties of Zr50.5Cu36.45Ni4.05Al9 alloy were improved largely due to the Nb addition. The room-temperature compressive fracture strength and plastic strain for Zr49.5Cu36.45Ni4.05Al9Nb1 rod with a diameter of 5 mm reaches 2037 MPa and 8%, respectively. The improvements are attributed to the precipitation of the spherical B2 CuZr phase distributed uniformly in amorphous matrix, which effectively hampers the propagation of shear bands by deflecting them at the interface and by a multiplication mechanism.

The emergence of organic electronics represents one of the most dramatic technological developments of the past two decades. Perhaps the most important frontier of this field involves the interface with biology. The “soft” nature of organics offers better mechanical compatibility with tissue than traditional electronic materials, while their natural compatibility with mechanically flexible substrates suits the nonplanar form factors often required for implants. More importantly, the ability of organics to conduct ions in addition to electrons and holes opens up a new communication channel with biology. In this article, we consider a few examples that illustrate the coupling between organic electronics and biology and highlight new directions of research.

To investigate the effects of substituting Ag and Sb for Pb on the thermoelectric properties of PbTe, the electronic structures of PbTe and AgPb18SbTe20 were calculated by using the linearized augmented plane wave based on the density-functional theory of the first principles. By comparing the differences in the band structure, the partial density of states (PDOS), the scanning transmission microscope, and the electron density difference for PbTe and AgPb18SbTe20, we explained the reason from the aspect of electronic structures why the thermoelectric properties of AgPb18SbTe20 could be improved significantly. Our results suggest that the excellent thermoelectric properties of AgPb18SbTe20 should be attributed in part to the narrowing of its band gap, band structure anisotropy, the much extrema and large DOS near Fermi energy, as well as the large effective mass of electrons. Moreover, the complex bonding behaviors for which the strong bonds and the weak bonds are coexisted, and the electrovalence and covalence of Pb–Te bond are mixed should also play an important role in the enhancement of the thermoelectric properties of the AgPb18SbTe20.

In our previous study, we modeled the indentation performed on an elastic–plastic solid with a rigid conical indenter by using finite element analysis, and established a relationship between a nominal hardness/reduced Young’s modulus (Hn/Er) and unloading work/total indentation work (We/Wt). The elasticity of the indenter was absorbed in Er ≡ 1/[(1 − ν2)/E + (1 − νi2)/Ei], where Ei and νi are the Young’s modulus and Poisson’s ratio of the indenter, and E and ν are those of the indented material. However, recalculation by directly introducing the elasticity of the indenter show that the use of Er alone cannot accurately reflect the combined elastic effect of the indenter and indented material, but the ratio η = [E/(1 − ν2)]/[Ei/(1 − νi2)] would influence the Hn/Er–We/Wt relationship. Thereby, we replaced Er with a combined Young’s modulus Ec ≡ 1/[(1 − ν2)/E + 1.32(1 − νi2)/Ei] = Er/[1 + 0.32η/(1 + η)], and found that the approximate Hn/Ec–We/Wt relationship is almost independent of selected η values over 0–0.3834, which can be used to give good estimates of E as verified by experimental results.

A late porogen removal scheme was used to make low-k materials (k = 2.72 to 2.02) using methylsilsesquioxane (MSQ) and a high-temperature porogen, poly(styrene-b-4-vinylpyridine) (PS-b-P4VP), to circumvent the reliability issues related to as-deposited porous dielectric. Based on the nanoindentation and Fourier transform infrared spectroscopy (FTIR) analysis, the moduli of the hybrid films were found to be higher than their porous forms, and even better than the dense MSQ film, for porogen loading below a critical level (˜69.5 vol%). This could be attributed to their enhanced degree of cross-linking in MSQ as evidenced by the network/cage structural ratios. Besides, high-temperature porogen plays different roles during the cross-linking of MSQ depending on its loadings. In this study, with immediate loading at 16.7 vol%, PS-b-P4VP can serve as plasticizer to enhance the degree of cross-linking, but at a large loading >16.7 vol%, it becomes a steric hindrance reducing the degree of cross-linking.

David Turnbull's experiments and theoretical insights paved the way for much of our modern understanding of phase transitions in materials. In recognition of his contributions, this lecture will concentrate on phase transitions in a material system not considered by Turnbull, thin diblock copolymer films. Well-ordered block copolymer films are attracting increasing interest as we attempt to extend photolithography to smaller dimensions. In the case of diblock copolymer spheres, an ordered monolayer is hexagonal, but the ordered bulk is body-centered cubic (bcc). There is no hexagonal plane in the bcc structure, so a phase transition must occur as n, the number of layers of spheres in the film, increases. How this phase transition occurs with nand how it can be manipulated is the subject of the first part of my presentation. In the second part of the talk, I show that monolayers of diblock copolymer spheres and cylinders undergo order-to-disorder transitions that differ greatly from those of the bulk. These ordered 2D monolayers are susceptible to phonon-generated disorder as well as to thermal generation of defects, such as dislocations, which, while they are line defects in 3D, are point defects in 2D. The results are compared to the theories of melting of 2D crystals (spheres) and of 2D smectic liquid crystals (cylinders), a comparison that will allow us to understand most, but not all, of the features of these order-disorder transitions that occur as the temperature is increased.

Self-assembled monolayers (SAMs) of organic dipolar molecules have new electronic and magnetic properties that result from their organization, despite the relatively weak interaction among the molecules themselves. Here we review the origin of this cooperative effect and summarize work performed on spin selective electron transmission through SAMs. The spin selectivity observed, in some cases, is consistent with a model in which a SAM containing chiral dipolar molecules behaves like a magnetic layer. The magnetic properties result in the SAMs behaving as spin filters, even without applying an external magnetic field to the layer.

BaTiO3 thin films were prepared on metallic foil substrates using chemical solution deposition. The impact of A to B site cation ratios on the phase assemblage and microstructural and dielectric properties was investigated by characterizing a sample set that includes stoichiometric BaTiO3 and 1, 2, 3, 4, and 5 mol% excess BaO. Each composition was subjected to a high-temperature anneal step with maximum dwell temperatures of 1000, 1100, and 1200 °C for 20 h. Excess barium concentrations greater than 3% lead to dramatic grain growth and average grain sizes exceeding 1 μm. Despite the large deviations from stoichiometry and the 20 h dwell time at temperature, x-ray diffraction, and high-resolution electron microscopy analysis were unable to detect secondary phases until films with 5% excess barium were annealed to 1200 °C. Thin films with 3% excess barium were prepared on copper substrates and annealed at 1060 °C, the practical limit for copper. This combination of BaO excess and annealing temperature produced an average lateral grain size of 0.8 μm and a room-temperature permittivity of 4000. This is in comparison to a permittivity of 1800 for stoichiometric material prepared using identical conditions. This work suggests metastable solubility of BaO in BaTiO3 that leads to enhanced grain growth and large permittivity values. This technique provides a new solid-state means of achieving grain growth in low thermal budget systems.

Polymer gels have potential use for a wide variety of applications, primarily due to the ability to tailor the gel properties by varying several material parameters. While substantial attention has focused on water-based hydrogels, the use of these materials is limited due to a narrow operational temperature range. This report describes a nonaqueous polymer gel, composed of a cross-linked polybutadiene network swollen with low volatility polymer plasticizers. Thermal, mechanical, and adhesive characterization illustrated that the gels exhibit performance over an extremely broad temperature range (−60–70 °C). Solvent quality and loading played a critical role in the operational temperature window with small solvent solubility parameter deviations dramatically reducing the operational temperature range. In addition, the processing conditions had a large impact on the gel mechanical properties. As a result, it is important to consider the influence of processing conditions and solvent quality when tailoring polymer gels for practical applications.

Application of high intensity electric pulse (HIEP) to a severely deformed eutectoid microstructure in high carbon steel wire has resulted in spheroidized microstructure. The observed spheroidization on electropulsing is compared with that reported for isothermal/thermo-mechanical annealing of the pearlite structure. The faster kinetics observed in this study has been rationalized in terms of accelerated kinetics induced by HIEP.

The microstructure of Pt-modified γ′-Ni3Al + γ-Ni coating on CMSX-4 single-crystal superalloy has been investigated by transmission electron microscopy (TEM). Cross-sectional TEM analyses showed the presence of precipitates in the coating. This precipitate was identified as the hexagonal topologically close-packed (TCP) μ phase with lattice parameters a = 0.473 nm and c = 2.565 nm. The energy-dispersive x-ray (EDX) spectrum of the μ phase suggested a refractory element rich compound comprising the elements Re, W, and Co. Twin domains parallel to (001) were found in the μ phase. The mechanisms of the μ phase and twinning formation were discussed.

The deformation behavior of amorphous selenium near its glass transition temperature (31 °C) has been investigated by uniaxial compression and nanoindentation creep tests. Cylindrical specimens compressed at high temperatures and low strain rates deform stably into barrel-like shapes, while tests at low temperatures and high strain rates lead to fragmentation. These results agree well with stress exponent and kinetic activation parameters extracted from nanoindentation creep tests using a similarity analysis. The dependence of the deformation modes on temperature and strain rate can be understood as a consequence of material instability and strain localization in rate-dependent solids.

The stress relaxation responses of the Sn–3.8Ag–0.7Cu joints following exposure to electrical currents were examined to investigate the effect of electromigration on the reliability of solder joints. It was found that the stress relaxation rate was enhanced for the Sn–3.8Ag–0.7Cu solder joints subjected to a current density of 2 × 104 A/cm2. Sn hillock formation was observed in situ on the surface of the solder joint and the increase of the hillock volume was obtained as a function of the current application time. Analysis of the vacancy flux indicated that the variations of the vacancy concentration with the electromigration time from the calculations agreed with the growth kinetics of the hillocks observed in the experiments. By modeling the stress relaxation as a climb-assisted dislocation glide process, it is shown that the vacancy accumulation induced by electromigration enhanced the dislocation climb rate, resulting in a large increase of the stress relaxation rate.

Blister features produced by laser-induced delamination of silicon dioxide from silicon substrates were analyzed with thin-film buckling mechanics. These analyses revealed the role of the interaction between the material and the femtosecond (fs)-pulsed laser on blister formation. In particular, it was deduced that the magnitude of the compressive residual film stress within the irradiated region appeared to exceed the intrinsic residual stress obtained from wafer curvature techniques. This apparent increase in the compressive stress after fs-pulsed laser irradiation may be caused by a modification of the oxide, which resulted in a local rarefaction of the film. The results demonstrated important features of the interaction between materials and fs-pulsed laser, including the presence of subtle modification thresholds and the limited role of thermal effects.

Thornlike Tb-doped SiC (SiC:Tb) nanostructures were synthesized through a carbothermal reduction of electrospun Tb-doped SiO2 nanofibers (SiO2:Tb). The synthesized SiC nanostructures annealed at a high temperature of 1300 °C displayed a unique morphology and a high crystalline quality with the β-SiC phase. Strong green-light emissions were detected from the SiC:Tb samples. Photoluminescence excitation results show that, besides a small amount of energy coming from the SiC cores (464 nm), most of the energy needed for the excitation of Tb3+ ions comes from the light absorption of the SiO2–Tb surface layers (295 nm) and near-interface regions in the samples (388 nm). Transmission electron microscopy, energy dispersive spectrometry, and Raman analyses suggested that the formations of Tb clusters and SiO2 surface layers are very important to the enhancement of the luminescence behaviors of Tb3+ ions. Finally, we have constructed an excitation model and further proposed an energy transfer mechanism for these thornlike SiC:Tb nanostructures.

Organic-based interfaces can possess a range of surprising electronic properties that are of intense interest from both the basic science and the applied research points of view. In this issue of MRS Bulletin, we provide state-of-the-art overviews of selected topics involving three complementary aspects of the electronic properties of organic-based interfaces: the nascent electronics technologies that would gain from improved understanding and control of such interfaces; the novel properties that organic-based interfaces may possess; and the experimental and theoretical challenges afforded by such studies.