Materials Literature
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We present an extensive first-principles study of the phonons in boron nitride nanotubes using density functional perturbation theory in the local density approximation. Based on the nonsymmorphic rod-group symmetry of the tubes, the Raman- and infrared-active modes at the $\ensuremath{\Gamma}$ point of the one-dimens…
The structural, electronic, and vibrational properties of small-radius single-walled BN nanotubes are studied using the density functional method with the local density approximation. The results show that the chirality preference of BN nanotubes observed in experiments may be explained from the relative stability of…
By means of high resolution neutron powder diffraction at low temperature we have characterized the structural details of ${\mathrm{La}}_{x}{\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{FeMoO}}_{6}$ $(0<~\mathrm{x}<~0.5)$ and ${\mathrm{Ca}}_{x}{\mathrm{Sr}}_{2\ensuremath{-}x}{\mathrm{FeMoO}}_{6}$ $(0<~x<~0.6)$…
The influence of average molar mass and shear on the crystallization of isotactic polypropylene ( i PP) has been studied. The Weissenberg number, a dimensionless parameter consisting of the product of the shear rate and a characteristic relaxation time (γ̇ 0 λ r ), provides a criterion to locate the morphological tran…
It is shown that it is possible to significantly modify optical spectra of Bragg multiple quantum well structures by introducing wells with different exciton energies. The reflection spectrum of the resulting structures is characterized by high contrast and tuning possibilities.
The lattice vibrations are determined in the quasi-harmonic approximation for elemental Au and Cu to twice their normal density by first-principles electronic band-structure calculations. It is found for these materials that the important moments of the phonon density of states can be obtained to high accuracy from sh…
To elucidate a novel pressure-temperature phase diagram of the quasi-one-dimensional mixed-stack charge-transfer (CT) complex TTF-CA, we study the quasi-one-dimensional spin-1 Blume-Emery-Griffith (BEG) model. In addition to the local charge transfer energy and the inter-stack polar (dipole-dipole) interaction, we tak…
We have investigated Pd nanowires theoretically, and found that, unlike either metallic or free atomic Pd, they exhibit Hund's rule magnetism. In long, monoatomic wires, we find a spin moment of 0.7 Bohr magnetons per atom, whereas for short, monoatomic wires between bulk leads, the predicted moment is about 0.3 Bohr…
We investigate the band structure of electrons bound on periodic curved surfaces. We have formulated Schrödinger's equation with the Weierstrass representation when the surface is minimal, which is numerically solved. Bands and the Bloch wavefunctions are basically determined by the way in which the ``pipes'' are conn…
We propose a theory of the origin of transport nonuniversality in disordered insulating-conducting compounds based on the interplay between microstructure and tunneling processes between metallic grains dispersed in the insulating host. We show that if the metallic phase is arranged in quasi-one-dimensional chains of…
We report studies of polycrystalline samples of the metallic ferromagnet ${\mathrm{Pr}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{CoO}}_{3}$ through measurements of the magnetization, ac magnetic susceptibility, resistivity, and specific heat. We find an unusual anomaly around ${T}_{A}=120\mathrm{K},$ much below the ferromagne…
We construct a diffuse-interface model of two-phase solidification that quantitatively reproduces the classic free boundary problem on solid-liquid interfaces in the thin-interface limit. Convergence tests and comparisons with boundary integral simulations of eutectic growth show good accuracy for steady-state lamella…
It is found that crystals of molecular nanomagnets exhibit enhanced magnetic relaxation when placed inside a resonant cavity. A strong dependence of the magnetization curve on the geometry of the cavity has been observed, providing indirect evidence of the coherent microwave radiation by the crystals. A similar depend…
First-principles pseudopotential density functional calculations are reported for hydrogen- and oxygen-related defects in crystalline pentacene $({\mathrm{C}}_{22}{\mathrm{H}}_{14}).$ It is shown that defects that perturb a carbon atom so as to remove its ${p}_{z}$ orbital from participation in the \ensuremath{\pi} sy…
The electronic structure of noble-gas solids is calculated within density functional theory's exact-exchange method (EXX) and compared with the results from the local-density approximation (LDA). It is shown that the EXX method does not reproduce the fundamental energy gaps as well as has been reported for semiconduct…
Three problems are considered in which inhomogeneous broadening can yield unusual consequences. One problem involves the energy levels of atoms moving within nanopores of nearly cylindrical cross section. A second involves atomic or molecular motion in a quasi-one dimensional interstitial channel within a bundle of ca…
New families of carbon single-walled nanotubes are proposed and their electronic structures are investigated. These nanotubes, called graphynes, result from the elongation of covalent interconnections of graphite-based nanotubes by the introduction of yne groups. Analogously to ordinary nanotubes, armchair, zigzag, an…
Current flow, considering a semiclassical electron--electric-field interaction and electron scattering by acoustic phonons, is studied in semiconducting zig-zag carbon nanotubes. The $\ensuremath{\pi}$-electronic band structure and the phonon spectrum of the nanotube are both calculated from graphene by the zone-foldi…
A method has been developed for visualizing the internal deformation fields in opaque materials during impact events using a combination of flash X-rays and digital speckle analysis. The random speckle pattern required for the digital speckle analysis is achieved by seeding the specimen with a layer of 20% coverage X-…
Focused ion beam (FIB) milling offers a novel approach to preparation of site-specific cross-sections of heterogeneous catalysts for examination in the transmission electron microscope (TEM). Electron-transparent sections can be obtained without the need to embed or grind the original sample. Because the specimen can…