Materials Literature
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The first examples of carbachlorins (1) have been synthesized by the “3 + 1” methodology. Unlike true chlorins, these structures resist further oxidation to porphyrin. However, these novel aromatic structures resemble the tetrapyrrolic species in that they retain strong red-shifted absorptions in their electronic spec…
The orthogonality strategy provides a logical design principle for aromatic columns and microporosity in molecular crystals. An orthogonal porphyrin–bisresorcinol derivative 1 forms an extensive hydrogen-bonded network in which the porphyrin rings are forced into columns; the large cavities left can incorporate guest…
A substantial enhancement in the nonlinear optical properties of three-dimensional NLO chromophores in which three or four 4′-dibutylaminoazobenzenyl moieties are connected through a central phosphonium ion (right) is observed relative to the corresponding one-dimensional compound. This contrasts with the linear optic…
A series of heterobimetallic complexes [(V IV O)L1Cu II (μ-OAC)(MeOH)](ClO 4 ) ( 1 ) and [(V IV O)L1M II (μ-OAc)(H 2 O)](ClO 4 )·H 2 O (M = Ni ( 2 ), Co ( 3 ), Fe ( 4 ), Mn ( 5 )) derived from a symmetric tetraaminodiphenol macrocyclic ligand H 2 L1 have been synthesized and characterized. The crystal structure of 1 h…
We have studied the microdomain pattern in a block copolymer system using a recently developed imaging technique. We observe pronounced registry of microdomains from layer to layer, the propagation and evolution of disclinations, and novel morphologies which form at the edge of an island. The imaging of the microdomai…
A recently developed computational strategy is applied to examine the influence of several factors on the exchange coupling constants of oxalato-bridged copper(II) binuclear complexes (shown schematically here); molecular topology, the nature of terminal ligands and selected structural parameters are discussed.
Control over calcium carbonate deposition in an in vitro system containing the major macromolecular components present in mollusk shell is shown to depend on the presence of a specific protein fraction in the appropriate microenvironment, in this case, silk fibroin adsorbed on β-chitin. Experiments with synthetic poly…
We present recent results on two attempts at understanding and utilizing large-scale simulations of magnetic materials. In the first study we consider massively parallel implementations on a Cray T3E of the n-fold way algorithm for magnetization switching in kinetic Ising models. We find an intricate relationship betw…
In this paper, the hyperfine quadrupole interaction at the Zr-Ti site of (PZT) polycrystalline samples is studied for the first time. Powders for x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9 and 1 were prepared and characterized by XRD. The lattice constants and space groups were obtained as functions of Ti concentration. PAC…
The temperature dependence of the acoustic dispersion relation, $\ensuremath{\Omega}(Q,T)$, has been determined across the liquid-glass transition in o-terphenyl using inelastic x-ray scattering in the $1--6{\mathrm{nm}}^{\ensuremath{-}1}$ momentum transfer ( $Q$) range. From this the infinite frequency sound velocity…
Resistance measurements in the ``normal'' state of $(\mathrm{TMTSF}{)}_{2}{\mathrm{PF}}_{6}$ under pressure for different magnetic field orientations show striking features below 5 K. We observe metallic behavior $(\frac{\mathrm{dR}}{\mathrm{dT}}>0)$ when the field is aligned along the intermolecular tunneling dire…
A microscopical model is proposed, describing the origin and properties of three closely spaced zero-phonon lines observed in the green Cu band in ZnO:Cu crystals labelled and . These excitations are known to be formed by a charge-transfer reaction with hole bound states. These lines are shown to originate from an int…
Experiments in which the Raman linewidth was measured as a function of temperature (7-1183 K) and pressure (0-400 bar) were performed on the (111) and (100) planes of single crystals of the cubic anti-fluorite . The temperature dependence of the lattice constant was determined by x-ray diffraction (11-295 K). From the…
The stability of the $\ensuremath{\epsilon}$ phase of zirconium hydride is studied using the pseudopotential plane wave method. The fluorite structure is mechanically unstable with respect to a tetragonal distortion. However, the minimum corresponding to $c>a$ is almost degenerate in energy with that for $c<a$.…
Taking into account the bilinear coupling between the tunneling protons and the displacements of the electron shells of the surrounding ${\mathrm{PO}}_{4}$ groups, we present a new model of hydrogen-bonded ferroelectrics. The model is an extension of both the tunneling model and the nonlinear polarizability model and…
We have made ferroelectric memory capacitors by depositing a SrBi2Ta2O9 thin film on a Si substrate separated by an ultrathin buffer layer of silicon nitride film. The hysteresis in the capacitance–voltage curves suggests a sizable memory window of 2 V with a programming voltage swing of ±7 V. The switching time is es…
Using first principles variable cell shape molecular dynamics, we predict a new structure for silica. This structure results from annealing $\ensuremath{\alpha}$-quartz at pressures near a major phonon instability. The new phase is obtained by rotations of ${\mathrm{SiO}}_{4}$ tetrahedra producing edge-sharing ${\math…
We extended the sensitivity of fluorescence polarization anisotropy measurements to the single molecule level by studying the polarization response of single fluorophores rapidly rotating in liquid. Comparison with a simple model calculation allows us to obtain information on the hindered motion as well as on the rota…
Computer simulations suggest that ultrathin metal wires should develop exotic, non-crystalline stable atomic structures, once their diameter decreases below a critical size of the order of a few atomic spacings. The new structures, whose details depend upon the material and the wire thickness, may be dominated by icos…
Photocrystallization of amorphous selenium (a-Se) films under illumination by polarized light with 632.8 or 647.1 nm wavelength has been studied by Raman spectroscopy. Preferential orientation of trigonal crystalline, selenium (t-Se) obtained as a result of photocrystallization has been observed, threefold c axis of t…