Materials Literature
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We performed temperature-dependent extended X-ray absorption fine structure (EXAFS) measurements on a series of nanocrystalline zirconia powders with different crystallite sizes. The results show that there is a tetragonal-to-cubic phase transition with reduction of crystallite size. The temperature dependence of the…
An accelerated route to the synthesis of dendritic macromolecules through the use of fractal components larger than the repeating unit is described. The first-generation bromide 1 and the second-generation novel branched AB4 monomer 2 can be used to prepare a highly regular fifth-generation poly(ether ester) dendrimer…
We report for the first time that doped nanocrystals of semiconductor can yield both high luminescent efficiencies and lifetime shortening at the same time. Nanocrystals of Mn-doped ZnS with sizes varying from 3.5 to 7.5 nm were prepared by a room temperature chemical process. These nanosized particles have an externa…
The LaFe13–xSix system is studied by X-ray diffraction and ac susceptibility measurements between 77 and 300 K. With the increase of the Si content x, a structural transition from cubic NaZn13-type structure to tetragonal Ce2Ni17Si9-type structure and three kinds of magnetic behavior are observed. At low x-values (1.4…
The structure of (Fe 0.6 ,Cr 0.2 ,Ni 0.2 )Sn is of the CoSn structure type with Fe, Cr and Ni disordered in the Co position. The structure contains a void surrounded by a 20-vertex polyhedron. The coordination polyhedra for Sn are hexagons and edge-capped trigonal prisms, and for Fe, ten-vertex polyhedra
Single-crystal films of 2-cyclooctylamino-5-nitropyridine have been prepared by the shear method, and the second-order susceptibility has been measured by second-harmonic generation. Polarization-dependent measurements in an a plate show that the maximum value of deff (~56 pm/V) is approximately 10 times larger than t…
The observation of shake-up satellites assigned to simultaneous excitation of 1s and 2p Mg core electrons in magnesium oxide and fluoride is reported. The presence of well-defined features due to KL double-electron excitations in x-ray photoemission spectra of these solid-state systems is assessed. Possible multiplet…
Abstract An investigation of the refractive index and third‐order nonlinear optical susceptibility χ (3) of two polypernigraniline derivatives, poly (4,4'‐diphenylimine methine) (PDPIM) and poly (4,4'‐diphenylimine p‐heptyloxybenzylidene) (PDPIHB) reveals effects of molecular structure on the linear optical and nonlin…
During pulsed laser deposition of thin films, a significant amount of energy is coupled to the laser-generated plasma. The fraction of the energy absorbed in the plasma is a function of the incident laser wavelength, time-dependent plasma dimensions, and electron density. Due to time-varying parameters, a quantitative…
Abstract Smooth, adherent films of the electrically conducting polypyrrole formed on surfaces in contact with unstirred aqueous solutions containing the pyrrole monomer and the oxidant, FeCl 3 . Contradictory reports in the literature concerning the influence of HCl on the growth rate and electrical conductivity of po…
Abstract The chemical reactions occurring in the melt mixing of nylon6/polycarbonate (Ny6/PC) at 240°C were investigated. The reaction of equimolar Ny6/PC blends can be reconciled within the overall scheme of an exchange reaction occurring with the attack of active amino terminals on the inner carbonate groups. We hav…
Spin-resolved and high-energy-resolution x-ray photoelectron spectroscopy (XPS) measurements of the 3s and 2s levels of metallic cobalt are reported. The high-resolution 3s spectrum shows a multiplet splitting \ensuremath{\Delta}${\mathit{E}}_{3\mathit{s}}$ of 3.3\ifmmode\pm\else\textpm\fi{}0.3 eV. The metallic value…
We present a variational calculation of the envelope wave function of an exciton inside a cube. We show that all sixfold integrals can be reduced to threefold integrals with a change of variables which shortens tremendously the computer calculations. Then (i) we calculate numerically the Bohr radius, the correlation e…
In situ x-ray-diffraction studies of nanophase TiO2 during annealing reveal a strong angular-dependent decrease in diffuse background intensities and a corresponding increase in rutile and anatase phase peak intensities for samples annealed above 623 K. This behavior is consistent with the crystallization of an amorph…
Partial monolayers of uniform length alkyl chains [CH3(CH2)n–; n=10–21] bonded at constant coverage onto a disordered lattice of silanol groups on amorphous SiO2, exhibit a distinct change in surface wetting behavior for 14≤n≤17 which correlates closely with a significant shift in the average conformational ordering o…
Light-emitting porous silicon films have been obtained by anodic etching p-type Si samples in a HF-ethanol solution. Porous Si samples efficiently luminesce at room temperature in the visible region. A degradation of the luminescence intensity with time is observed. Micro-Raman spectroscopy of free-standing porous sil…
The structure and magnetic properties of nanocrystalline, two-phase Sm2Fe17Nx+α-Fe alloys prepared by mechanical alloying and heat treatment have been studied. Remanence enhancement and single-phase magnetic behavior were observed in isotropic powders crystallized at low temperatures (about 600 °C), while crystallizat…
Molecular dynamics simulation of a united-atom polyethylene model was performed to study the short time dynamics of polymer liquid and glass. Simulation runs lasting up to 5 ns were performed at ten temperatures above and below the estimated glass transition temperature. Quantities evaluated for the purpose of studyin…
Electron energy loss spectroscopy and high-resolution images of carbon nanotubes, obtained using a 2 nm probe and energy resolution of 0.5 eV, revealed a 15 eV surface plasmon for tubes containing \ensuremath{\le}12 cylindrical graphitic sheets. As the number of sheets increases further the 24 eV bulk plasmon quickly…
Abstract The dielectric properties of poly(vinyl‐chloride) (PVC) were investigated as a function of frequency and temperature. Attention was focused on the low frequency dielectric properties. Samples with different molar masses were studied. Two dipolar retardation processes were observed, one due to a local motion i…