Materials Literature
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Lewis acid and Lewis base centers are simultaneously present in the boron-bridged thiophene-containing porphyrinogen 1 that has been synthesized in high yield. Its crystal structure reveals a nonplanar macrocycle; this and the colorless aspect suggest the absence of a delocalized π-electron system. R = NiPr2.
The liquid crystalline behavior of compounds 1 (n = 7, 12, 15) differs significantly from that exhibited for conventional rodlike molecules. They organize into layered smectic, bicontinuous cubic or hexagonal columnar mesophases depending on the temperature or the volume fraction of coil segments.
A first-principle molecular dynamics study on liquid $\mathrm{GeSe}{}_{2}$ yields structural properties in good agreement with detailed neutron scattering data. The short range order is accurately described by a variety of bonding configurations, in which regular tetrahedra coexist with an important fraction of homopo…
The pH-dependent self-condensation of the [Mo2S2O2]2+ complex fragment gives the wheellike Mo12 cluster depicted on the right (ball-and-stick model; large balls: S, medium balls: O, small balls: Mo). Applying this synthetic strategy to other starting materials could provide access to other polyoxothiometalates with we…
To understand the origin of the second long-length scale in $\mathrm{SrTiO}{}_{3}$, we studied structural defects in Verneuil-grown single crystals by transmission electron microscopy. The density of the dislocations was observed to decrease with increasing depth from the original cut surface of the crystals. The high…
Electromigration-induced stress distributions in 200 μm long, 10 μm wide aluminum conductor lines in 1.5 μm SiO2 passivation layers have been investigated in real time using synchrotron-based white-beam x-ray microdiffraction. The results show that a steady-state linear stress gradient along the length of the line dev…
$(\mathrm{RE}){\mathrm{Ni}}_{0.3}{\mathrm{Co}}_{0.7}{\mathrm{O}}_{3}$ $(\mathrm{RE}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\mathrm{L}\mathrm{a},\mathrm{N}\mathrm{d},\mathrm{S}\mathrm{m})$ oxides with the perovskite structure have been studied. All of these compounds show a spin-glass behavior at low tempera…
Highly tetrahedral hydrogenated amorphous carbon (ta-C:H) is deposited with a novel, 13.6 MHz excited electron cyclotron wave resonance (ECWR) plasma source. The ion flux of an acetylene and a nitrogen plasma was investigated by mass spectrometry and retarding field measurements. The ECWR gives a dissociation degree b…
The incoherent dynamic structure factor of orthoterphenyl is studied by quasielastic neutron scattering to 240 MPa. Tagged-particle correlations in the compressed liquid decay in two steps. The $\ensuremath{\alpha}$-relaxation line shape is independent of pressure, and the relaxation time proportional to viscosity. A…
Remarkable thermal stability is exhibited by [FeII(tcne)2]⋅x CH2Cl2 (57Fe Mössbauer spectra reveal that the oxidation state of iron is II), which was prepared by treating the MeCN solvate of FeI2 with tetracyanoethylene (TCNE). This method, which can also be applied to synthesize the analogous Mn, Co, and Ni compounds…
BaTiO 3 /SrTiO 3 multilayered thin films were deposited on Si and Pt/Si substrates. X-ray diffraction clearly shows the formation of the superstructures. Phase transition properties were studied via dielectric measurements. Glassy behavior, characterized by a strong frequency dispersion of dielectric properties, was f…
A convergent synthesis in which all trans double bonds were constructed by Wittig-Horner reactions produces dendrimers of the general structure 1. With long-chain alkoxy residues on the periphery of the benzene rings, the first two generations display liquid crystalline behavior.
The observation of unusually large, positive and rare-earth dependent $^{16}O\mathrm{\ensuremath{-}}^{18}O$ isotope shifts in the metal-insulator transition temperature ${T}_{\mathrm{MI}}$ of $R\mathrm{NIO}{}_{3}$ perovskites is reported $(\ensuremath{\Delta}{T}_{\mathrm{MI}}\ensuremath{\le}+10.3\mathrm{K})$. The resu…
The energy diagram of ${\mathrm{Mn}}_{12}$-acetate is probed close to the top of the anisotropy barrier using a novel, high-sensitivity, electron paramagnetic resonance technique. Multiple resonances, and their temperature dependence, are observed from 35 to 115 GHz, for a single high-quality crystal. The data are suf…
Amphiphilic block copolymer templates in sol-gel processes yield bicontinuous silicates with distorted hexagonal symmetry (see, for example, the transmission electron migrograph depicted on the right). The long Bragg distance of 8-13 nm combined with the high mechanical and thermal stability suggests some promising pr…
Extensive molecular dynamics simulations are performed on a glass-forming Lennard-Jones mixture to determine the nature of the cooperative motions occurring in this model fragile liquid. We observe stringlike cooperative molecular motion (``strings'') at temperatures well above the glass transition. The mean length of…
The room-temperature modulated structure of ${\mathrm{NbTe}}_{4}$ was studied by means of scanning tunneling microscopy. In addition to a relatively weak image of the average structure and stronger contrast from the incommensurate modulation, contributions from domains of nanometer sizes were detected, which appeared…
To control in situ oxygen fugacity in a sample at high temperature and high pressure, the oxygen pump that is usually used at ambient pressure was introduced into a high‐pressure system in the present work. Inside the sample assembly, an oxygen buffer was used as an oxygen reservoir. By means of our high‐pressure oxyg…
The interplay between the electron repulsion $U$ and the Jahn-Teller electron-phonon interaction ${E}_{\mathrm{LR}}$ is studied with a large-$d$ model for the ferromagnetic state of the manganese oxides. These two interactions collaborate to induce local isospin (orbital) moments and to reduce the bandwidth $B.$ The r…
Electron scattering factors of ions are represented in a parametrized form which separates the diverging Coulomb term due to ionic charge from the contribution of the screened atomic field. Using this representation it is shown how dynamical reflection high-energy electron diffraction (RHEED) calculations can be perfo…