Changes in the structure of Ti5Si3 were measured by x-ray and neutron diffraction as carbon, nitrogen, or oxygen atoms were systematically incorporated into the lattice. Additionally, the lattice parameters and variable atomic positions of pure Ti5Si3 were determined to be a = 7.460 Å, c = 5.152 Å, xTi = 0.2509, and xSi = 0.6072. The measured trends in lattice parameters as carbon, nitrogen, or oxygen atoms were added to Ti5Si3 showed that most of the previous studies on supposedly pure Ti5Si3 were actually contaminated by these pervasive light elements. Also, oxygen and carbon additions were shown to strongly draw in the surrounding titanium atoms—evidence for bonding between these atoms. The bonding changes that occurred on addition of carbon, nitrogen, or oxygen acted to decrease the measured anisotropic properties of Ti5Si3, such as thermal expansion.

The crystallographic thermal expansion coefficients of Ti5Si3 from 20 to 1000 °C as a function of B, C, N, O, or Ge content were measured by high-temperature x-ray diffraction using synchrotron sources at Cornell University (Cornell High Energy Synchrotron Source; CHESS) and Argonne National Laboratory (Advanced Photon Source; APS). Whereas the ratio of the thermal expansion coefficients along the c and a axes was approximately 3 for pure Ti5Si3, this ratio decreased to about 2 when B, C, or N atoms were added. Additions of O and Ge were less efficient at reducing this thermal expansion anisotropy. The extent by which the thermal expansion was changed when B, C, N, or O atoms were added to Ti5Si3 correlated with their expected effect on bonding in Ti5Si3.

We recently proposed a theory of mechanism-based strain gradient (MSG) plasticity to account for the size dependence of plastic deformation at micron- and submicronlength scales. The MSG plasticity theory connects micron-scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor's dislocation hardening model to strain gradient plasticity. Here we show that the theory of MSG plasticity, when used to study micro-indentation, indeed reproduces the linear dependence observed in experiments, thus providing an important self-consistent check of the theory. The effects of pileup, sink-in, and the radius of indenter tip have been taken into account in the indentation model. In accomplishing this objective, we have generalized the MSG plasticity theory to include the elastic deformation in the hierarchical framework.

New low-dielectric-constant interlevel dielectrics are being investigated as alternatives to SiO2 for future integrated circuits. In general, these materials have very different mechanical properties from SiO2. In the standard model, electromigration-induced stress evolution caused by changes in the number of available lattice sites in interconnects is described by an effective elastic modulus, B. Finite element calculations were carried out to obtain B as a function of differences in the modulus, E, of interlevel dielectrics, for several stress-free homogeneous dilational strain configurations, for several line aspect ratios, and for different metallization schemes. In contradiction to earlier models, we found that for Cu-based metallization schemes with liners, a decrease in E by nearly two orders of magnitude has a relatively small effect on B, changing it by less than a factor of 2. However, B, and therefore the reliability of Cu interconnects, can be strongly dependent on the modulus and thickness of the liner material.

Two kinds of obviously different-sized –Si3N4 whiskers were grown from silicon melt with different pretreatment vacuum conditions. Their growth interface structures were studied in a cross-section view from micro-areas to macro-areas by combination of micro-area state analysis with chemical shift mapping of Si Kβ bands using electron probe microanalysis. The one pretreated under the lower vacuum condition with a rotary pump was 10–20 μm in diameter and hundreds of micrometers in length, and another pretreated under the higher vacuum condition with a diffusion pump was 0.1–0.2 mm in diameter and 2–5 mm in length. The small Si3N4 whiskers were grown from the surface of the SiC particles within the Si melt. The large Si3N4 whiskers were grown from the surface of Si3N4 crucible. On the basis of these results, their growth mechanisms are discussed from the view of the nucleation sites, impurity source, and thermodynamic stability of the SiC particles. Compared with the Si3N4 grains, the SiC particles influenced the nucleation deeply and caused the process to grow small-sized crystals. Preventing the carbon impurities into the Si melt from forming the SiC particles in the pretreatment process was one effective way to grow the large-sized β–Si3N4 single crystals.

The structural and electronic properties of (CdTe)1−x(In2Te3)x thin films as a function of substrate temperature were studied using x-ray diffraction, energy dispersive x-ray analysis, and Raman, transmission, and modulated transmission spectroscopies. The films were grown by the close-spaced vapor transport technique combined with free evaporation; CdTe and In2Te3 were used as sources. From x-ray diffraction the presence of mixed phases and differences in composition were detected, and good correlation with Raman spectroscopy was found. Transmission spectroscopy suggested the possibility of a modulation of the band gap of the alloy from a value as low as 0.5 eV up to 1.5 eV. Single-phase films presented a direct band gap of around 1.15 eV, as obtained from modulated transmission measurements.

We fabricated Bi nanowire array composites with wire diameters from 30 to 200 nm by high-pressure injection (HPI) of Bi melt into porous anodic alumina templates. The composites were dense, with Bi volume fraction in excess of 50%. The parallel Bi nanowires, whose length appeared to be limited only by the thickness of the host template (up to 55 μm), terminated at both sides of the composite in the Bi bulk. The individual Bi nanowire crystal structure was rhombohedral, with the same lattice parameters as that of bulk Bi; the wires in the array were predominantly oriented with the trigonal axis along the wire length. Low contact resistance was achieved by bonding the composite to copper electrodes.

Carbon nanotubes, typically of 0.5-μm length and 20-nm diameter, were prepared with good selectivity by disproportionation of CO in He over a Pd/La2O3 catalyst. The catalyst was formed in situ by reduction of a La4PdO7 precursor. The obtained nanotubes had the so-called fishbone structure with the graphitic planes inclined at an angle to the long axis of the nanotube. The effect of CO concentration was studied at 673 °C, and it was found that, among the concentrations studied, 20 vol% CO in the gas was suitable for nanotube growth. The obtained nanotube/La2O3/Pd composite contained typically only 3 wt% nanotubes after 8 h of CO treatment. A process for selective dissolution of La2O3 and Pd was applied, and a product containing 85 wt% nanotubes was obtained. The nanotubes were characterized by high-resolution, transmission, and scanning electron microscope studies, combined with element analyses using energy dispersive spectrometers, x-ray powder diffraction studies, and thermogravimetric analysis.

Nickel thin films were deposited with Ni(C5H5)2 \NiCp2, bis(cyclopentadienyl)nickel, nickelocene]/H2 at various temperatures and H2/Ar ratios. The deposition rate, resistivity, purity, crystal structure, and surface morphology of the nickel film were investigated. Also, thermal analysis was done to find out the dissociation characteristics of NiCp2, and Fourier transform infrared spectroscopy diagnostics were carried out to study the gas phase reaction kinetics of NiCp2. Nickel films deposited at higher temperatures (>225 °C) had high carbon content and high resistivity. At higher temperatures, thermal decomposition of NiCp2 and subsequent decomposition of Cp induced a large amount of carbon incorporation into the film. At lower temperatures (<190 °C), the slow dissociation of NiCp led to some extent of carbon incorporation in the film. Nickel films deposited at around 200 °C showed carbon content lower than 5% and lower resistivity because of the effective dissociation of Ni–Cp and desorption of Cp from the surface. Nickel films deposited with hydrogen addition showed higher purity, crystallinity, and lower resistivity due to the removal of the carbon on the surface.

Thin-film composites of BaTiO3 particles in a polymeric matrix were processed by reacting films of a titanium alkoxide, mixed with a polybutadiene-polystyrene triblock copolymer, in aqueous solutions of 1.0 M Ba(OH)2 at temperatures ranging from 60 to 90 °. After reaction, the composite films displayed distinct surface and subsurface morphologies. The film surface consisted of a continuous layer of BaTiO3 grains, the film grain size decreasing from 180 to 60 nm as the reaction temperature increased from 60 to 90 °. The subsurface growth of BaTiO3 depended on the presence of a percolating network of hydrolyzed titanium alkoxide, which enabled the reaction solution to permeate throughout the thin film. The resulting subsurface film morphology was composed of segregated regions of BaTiO3 particles dispersed throughout the polymeric matrix. The growth of subsurface BaTiO3 particles appeared to be constrained by the polymer matrix, resulting in a subsurface particle size of approximately 5 to 10 nm that was independent of the hydrothermal processing temperature. The reacted films displayed a dielectric constant ranging from 10 to 15 at room temperature and a frequency of 10 kHz.

Commercially available poly(propylene)imine (DAB-Am-32 and DAB-Am-64) dendrimers were used as single-molecule templates to tailor the porosity of silicas via a nonacidic sol-gel method. X-ray diffraction on both the as-prepared (oven-dried at 373 K) and the calcined (833 K) materials revealed that modest contraction took place on template removal and that the cavities created did not achieve three-dimensional ordering under the current synthesis conditions. Transmission electron microscopy of “Pt-stained” samples supported this picture. A modified Horvath–Kawazoe analysis of the argon adsorption isotherms indicated that DAB-Am-64 is a much more effective template than DAB-Am-32. Pyrolysis and oxidation protocols for template removal are also presented.