Materials Literature
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Spectral properties of blue upconversion luminescences in Tm3+ doped tellurite (PWT, PbF2-WO3-TeO2) glasses and germanate (PWG, PbF2-WO3-GeO2) glasses pumped by a tunable dye laser were studied at room temperature. Two emission bands centered at 453 and 477 nm, corresponding to the D21→H43 and G41→H63 transitions of T…
Antiferroelectric behavior is observed in artificially layered KTaO (3)/KNbO (3) perovskite superlattices. While KTaO (3) and KNbO (3) are ferroelectric and paraelectric, respectively, the superlattice appears antiferroelectric based on an increase in the dielectric constant with applied dc bias. This dielectric behav…
Electronic structures of the hexagonal ${\mathrm{Ti}}_{2}\mathrm{AlC}$ and ${\mathrm{Ti}}_{2}\mathrm{AlN}$ compounds with ${\mathrm{Cr}}_{2}\mathrm{AlC}$-type structure calculated within the full-potential linearized augmented plane-waves formalism are presented. Geometrical optimization of the unit cell are in good a…
The development of a sensitive porous silicon (PS) gas sensor which utilizes photoluminescence induced electroless metallization as a means of obtaining a highly efficient electrical contact has been demonstrated for the detection of HCl, NH3, and NO at the 10 ppm level. The problem of spreading resistance (kΩ–MΩ) is…
The phase distribution of high aspect ratio, Fe-filled carbon nanotubes prepared by pyrolyzing a mixture of powered ferrocene and ${\mathrm{C}}_{60}$ has been determined by means of M\"ossbauer spectroscopy. Our results for that characterization are closely related to the observation, after field cooling processes, of…
A nonlithographic technique that utilizes highly ordered anodized aluminum oxide porous membrane as template is presented as a general fabrication means for the formation of an array of vastly different two-dimensional lateral superlattices structures. Hexagonal close-packed nanopore arrays were fabricated on Si, GaAs…
The fundamental optical absorption of Cs 4 PbBr 6 crystals, which are built up of nearly regular Pb 2+ (Br - ) 6 octahedra mutually bound by Cs + ions, exhibits novel features: despite the crystalline entity of Cs 4 PbBr 6 , it shows oscillator-like absorption peaks and a wide window just above the first peak. The Cs…
Magnetische Lawinen: Ein chiraler, polymerer Mangan(II)-Komplex mit einem enantiomerenreinen Nitronylnitroxid-Liganden (siehe Struktur der Wiederholungseinheit; O rot, N grün, Mn blau) zeigt ungewöhnliches magnetisches Verhalten. Bei 3 K liegt im Festkörper magnetische Ordnung vor, unterhalb von 0.3 K jedoch wurden dy…
Magnetic avalanches: A chiral polymeric manganese(II) complex with an enantiopure nitronyl nitroxide ligand (see structure of repeating unit; red: oxygen, green: nitrogen, blue: manganese) shows unusual magnetic behavior. The polymer orders magnetically in the bulk at 3 K, and reveals unusual dynamic and hysteretic ma…
We present a new method, in the following called MMM2D, to accurately calculate the electrostatic energy and forces on charges being distributed in a two dimensional periodic array of finite thickness. It is not based on an Ewald summation method and as such does not require any fine-tuning of an Ewald parameter for c…
The mean-field Landau-type theory is used to analyze the polarization properties of epitaxial ferroelectric thin films grown on dissimilar cubic substrates, which induce biaxial compressive stress in the film plane. The intrinsic effect of the film surfaces on the spontaneous polarization is taken into account via the…
The electronic band structure of GaTe is calculated by numerical atomic orbital density-functional theory, in the local-density approximation. In addition, the valence-band dispersion along various directions of the GaTe Brillouin zone is determined experimentally by angle-resolved photoelectron spectroscopy. Along th…
We prepared polycrystalline samples of the A x BO 2 -type layered oxides Na 0.77 MnO 2 and LiCoO 2 , and measured thermal conductivity (κ) from 15 to 280 K. Na 0.77 MnO 2 shows a low κ of 15 mW/cmK at 280 K, while LiCoO 2 shows a much higher κ of 40 mW/cmK at 280 K. By comparing these results with κ of NaCo 2 O 4 , we…
A comprehensive theory of quantum spin relaxation in ${\mathrm{Mn}}_{12}$ acetate crystals is developed that takes into account imperfections of the crystal structure and is based upon the generalization of the Landau-Zener effect for incoherent tunneling from excited energy levels. It is shown that linear dislocation…
The effect of confinement on the exciton binding energies has been systematically investigated for two series of ZnO/ZnMgO multiquantum wells with various well widths and barrier heights. The exciton binding energies were extracted from the energy difference between the stimulated emission band induced by inelastic ex…
Enhancement of remanent polarization has been demonstrated in epitaxial “asymmetric” BaTiO3/SrTiO3 strained superlattices, in which the thickness ratio of BaTiO3 to SrTiO3 layers is changed at molecular layer order accuracy. The superlattices have been prepared on Nb-doped SrTiO3 (100) single-crystal substrates by a p…
To investigate cylindrical ultrathin copper nanowires, we performed atomistic simulations using the steepest descent method. The stable structures of the cylindrical ultrathin copper nanowires were multi-shell packs composed of coaxial cylindrical shells with {111}-like surfaces. Semiclassical orbits in a circle and c…
We have determined the crystal structure of the composite crystal [Ca 2 CoO 3 ] 0.62 CoO 2 , known as Ca 3 Co 4 O 9 , by a superspace group approach. Structural parameters were refined with a superspace group of C m (0 1- p 0) using powder X-ray and neutron diffraction data. The compound consists of two interpenetrati…
In Mn1−xZnxFe2O4 (x=0 to 1) nanosize particles prepared through hydrothermal precipitation we observe a decrease in particle size from 13 to 4 nm with increasing Zn concentration from 0 to 1. The lattice constant, a, for all Mn/Zn concentrations is found to be less than that for the corresponding bulk values. At speci…
Accurate estimates of the magnetic coupling in binuclear complexes can be obtained from ab initio configuration interaction (CI) calculations using the difference dedicated CI technique. The present paper shows that the same technique also provides a way to analyze the various physical contributions to the coupling an…