Materials Literature
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The in situ observation of thermal alteration of photoinduced optical anisotropy of ultrathin films of polymethacrylates having p-cyanoazobenzene side chains exhibiting amorphous, crystalline, and liquid-crystalline phases was performed by means of temperature scanning ellipsometry. Whereas photogenerated optical anis…
Magnetic susceptibility of partially aligned multiwalled carbon nanotubes has been studied using superconducting quantum interference device magnetometry. Partial alignment of multiwalled nanotubes was produced by uniaxially straining composites of carbon nanotubes embedded in polymer matrices. The degree of alignment…
We have investigated the dynamic formation of silicon nanoparticles after pulsed-laser ablation of a silicon target into argon gas, in order to fabricate the nanoparticles that exhibit visible photoluminescence with higher efficiency. The nanoparticles growing in argon gas were detected by measuring plasma emission re…
A series of phenylbithiophene stilbenes and phenyltetraenes were synthesized and their first-order molecular hyperpolarizabilities determined. Optical nonlinearities up to μβo=9300×10−69 C m5/V were measured at 1907 nm. We show that intermolecular interactions have a large influence on the optical nonlinearity of the…
A micrometer-sized spherical microcavity, the photonic dot, is made from semiconductor nanocrystals, the quantum dots. The coupling of electronic and photonic states is demonstrated for a single photonic dot by the observation of whispering gallery modes in the spectrum of spontaneous emission of the embedded CdSe qua…
High-quality lead zirconate titanate films (PZT) have been grown on yttrium barium copper oxide (YBCO) bottom electrode by domain epitaxy where integral multiples of lattice constants match across the interface. The YBCO films were epitaxially fabricated on Si (100) by introducing epilayer geometry of strontium titana…
We conduct a theoretical study of the temperature dependence of the spin polarization ( P) and the magnetoresistance (MR) ratio using the double exchange (DE) model for ferromagnetic tunnel junctions with half-metallic systems. It is shown that the strong exchange coupling in the DE model plays an important role in th…
Silicon (Si) nanocrystallites have been synthesized using pulsed-laser ablation in inert background gases, for studying the structures and optical properties as one of the quantum confinement effects. We extracted a process condition where well-dispersed Si nanocrystallites devoid of droplets and debris are prepared,…
Squashing brings circumferentially separated areas of a carbon nanotube into close proximity, drastically altering the low-energy electronic properties and (in some cases) reversing standard rules for metallic versus semiconducting behavior. Such a deformation mode, not requiring motion of tube ends, may be useful for…
We here study electronic structure and magnetic properties of disordered CoPd and CoPt alloys using Augmented Space Recursion technique coupled with the tight-binding linearized muffin tin orbital (TB-LMTO) method. Effect of short range ordering present in disordered phase of alloys on electronic and magnetic properti…
We present calculations of the one- and two-particle excitations in silicon nanocrystals. The one-particle properties are handled in the GW approximation, and the excitonic gap is obtained from the Bethe-Salpeter equation. We develop a tight binding version of these methods to treat clusters up to 275 atoms. The self-…
A theory of scattering by charged dislocation lines in a two-dimensional electron gas (2DEG) is developed. The theory is directed towards understanding transport in AlGaN/GaN high-electron-mobility transistors (HEMT), which have a large number of line dislocations piercing through the 2DEG. The scattering time due to…
The full set of partial structure factors for the prototypical network glass GeSe2 was measured using the method of isotopic substitution in neutron diffraction. The basic building block of the network is the Ge(Se(1/2))(4) tetrahedron in which 34(5)% of the Ge reside in edge-sharing configurations. The intrinsic chem…
Two transitions in the bonding are found in tetrahedral amorphous carbon (ta-C) films as a function of deposition temperature. The total sp3 fraction shows a sharp decrease at a transition temperature of order 250 °C. In contrast, visible Raman finds that the sp2 sites show a gradual ordering into the graphitic cluste…
A highly substituted side chain NLO poly( p -phenylene) (∼70.1 wt % NLOphore) has been prepared by the nickel-catalyzed coupling of 4‘-( N, N -diethylamino)-2,5-dichlorobenzophenone. Poly((4‘- N, N -diethylamino)-2,5-benzophenone), PDEABP, is a modest molecular weight material ( M n = 5300) that is thermally stable up…
IM7 PAN-based carbon fibers, with a proprietary surface treatment applied by the manufacturer, were analyzed by X-ray photoelectron spectroscopy (XPS). The surface treatment applied by the manufacturer was removed by heating in a vacuum. The fibers detreated in this manner were then subjected to electrochemical treatm…
The development of cost-effective nanopowder production methods has been a major obstacle to the development and industrial utilization of nanostructured materials. This paper describes a new cost-effective production technology for these materials which combines both pulsed electrochemistry and pulsed ultrasound. Thi…
The Suzuki polycondensation of the amphiphilically equipped dibromobenzene derivatives 8 and 11 with benzene diboronic acid ester 12 to the new kind of polymeric amphiphiles 13 and 14 is described. They carry at each repeat unit either a hydrophobic alkyl chain and a hydrophilic dendron with oligoethyleneoxy chains (…
Polythiophene−transition metal hybrid materials based on cobalt salen have been prepared and shown to catalyze the reduction of O2. The conjugated nature of the polymer backbone allows for facile electron transfer from the polymer surface to the active metal centers to affect this reduction. Rotating ring−disk measure…
A chiral cyclohexane containing two photochromic diarylethene units was synthesized in an attempt to use it as a dopant for a photoresponsive liquid crystal. A stable photoswitching between nematic and cholesteric phases could be induced by the addition of a small amount of the chiral cyclohexane to a nematic liquid c…