Materials Literature
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The synchrotron powder diffraction beamline B2 at HASYLAB/DESY is described. The beamline is capable of high-resolution powder diffraction as well as time-resolved studies and offers several sophisticated ancillary equipments for special applications. A newly developed image-plate system allows for kinetic studies wit…
The stability and bonding of the ternary complex K$_2$PtCl$_6$ structure hydrides is discussed using first principles density functional calculations. The cohesion is dominated by ionic contributions, but ligand field effects are important, and are responsible for the 18-electron rule. Similarities to oxides are discu…
Structural and superconducting properties of magnesium diboride thin films grown by pulsed laser deposition on zirconium diboride buffer layers were studied. We demonstrate that the ZrB2 layer is compatible with the MgB2 two step deposition process. Synchrotron radiation measurements, in particular anomalous diffracti…
We have investigated beating patterns in Shubnikov-de Haas oscillations for HgTe/Hg_{0.3}Cd_{0.7}Te(001) quantum wells with electron densities of 2 to 3 X 10^{12} cm^{-2}. Up to 12 beating nodes have been observed at magnetic fields between 0.9 and 6 T. Zero magnetic field spin-orbit splitting energies up to 30 meV ha…
We report on a direct experimental evidence of shot noise in a linear macroscopic resistor. The origin of the shot noise comes from the fluctuation of the total number of charge carriers inside the resistor associated with their diffusive motion under the condition that the dielectric relaxation time becomes longer th…
The optical properties of Mn–Mg-codoped epitaxial GaN were studied. Addition of Mg acceptors quenches the weak manganese-related photoluminescence (PL) band at 1.3eV in GaN:Mn and a series of sharp PL peaks are observed at 1eV in codoped epilayers. The change in PL spectra indicates that the Mg addition stabilizes the…
Epitaxial La0.67Sr0.33MnO3(LSMO)∕SrRuO3(SRO) ferromagnetic bilayers have been grown on (001)SrTiO3(STO) substrates by pulsed laser deposition with atomic layer control. We observe a shift in the magnetic hysteresis loop of the LSMO layer in the same direction as the applied biasing field (positive exchange bias). The…
We propose a generalized stochastic Landau-Lifshitz equation and its corresponding Fokker-Planck equation for the magnetization dynamics in the presence of spin transfer torques. Since the spin transfer torque can pump a magnetic energy into the magnetic system, the equilibrium temperature of the magnetic system is il…
Tetranuclear Fe(II) cubic complexes were synthesized with Schiff base ligands bridging the Fe(II) centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4].2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4].2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4].MeOH (5), and [Fe4(3,5…
We present the design and construction of a SQUID-based magnetometer for operation down to temperatures T = 10 mK, while retaining the compatibility with the sample holders typically used in commercial SQUID magnetometers. The system is based on a dc-SQUID coupled to a second-order gradiometer. The sample is placed in…
The Brillouin elastic free energy change $DF$ between thermally annealed and quenched $(Na_2O)_x(SiO_2)_{1-x}$ glasses is found to decrease linearly at $x > 0.23$ (floppy phase), and to nearly vanish at $x < 0.18$ (stressed- rigid phase). The observed $D F(x)$ variation closely parallels the mean-field floppy mode fra…
We present the results of measurements of the thermal conductivity of Cu2Te2O5Br2, a compound where tetrahedra of Cu^{2+} ions carrying S=1/2 spins form chains along the c-axis of the tetragonal crystal structure. The thermal conductivity kappa was measured along both the c- and the a-direction as a function of temper…
It was suggested method of constructing of irreducible projective representations in different points of Brilluin zone. Points Γ, Λ, Z, S, A, Σ, M, V, R, and X of space symmetry groups $P4_{1}2_{1}2$ and $P4_{3}2_{1}2$ were examined. At each of these points one- and two-valued irreducible projective representations of…
We present an experimental investigation of heavy doping-induced many-body effects such as band gap narrowing(BGN) and Fermi edge singularity(FES) in Al$_x$Ga$_{1-x}$As using photoluminescence(PL) spectroscopy. The band-to-band transition energy shifts to lower energies and FES-like feature in PL spectra grows with in…
It is commonly assumed that cellulose from higher plants contains the Ialpha and Ibeta crystalline allomorphs together with surface and disordered chains. For cellulose Ialpha, the evidence for its presence in higher plants is restricted to the C-4 signals in the solid-state (13)C NMR spectrum, which match those of cr…
The entropy production is a non-negative quantity based on irreversible thermodynamics and thus serves as a basis for the systematic description of the irreversible processes occurring in a solid. In this paper, a thermodynamic framework has been presented for damage mechanics of solid materials, where entropy product…
We have investigated the properties of ZnMgO epilayers and ZnO–ZnMgO quantum well structures grown by metalorganic vapor-phase epitaxy. A well-controlled incorporation of magnesium, x⩽0.10, could be confirmed resulting in a blueshift of the photoluminescence emission wavelength of the Zn1−xMgxO layers up to 200meV. Us…
Abstract Reaktionen zur selektiven Veredelung von Alkenen zählen zu den wichtigsten Methoden in der Organischen Synthese. Durch die Entwicklung von Übergangsmetallkatalysatoren in den letzten Jahrzehnten können heute alle Arten von Selektivität bei einer Vielzahl von Transformationen effizient gesteuert werden. Auch 1…
The adsorption of molecular hydrogen on boron nitride nanotubes is studied with the use of the pseudopotential density functional method. The binding energy and distance of adsorbed hydrogen is particularly calculated. It is found that the binding energy of hydrogen on boron nitride nanotubes is increased by as much a…
Abstract Die selektive aerobe Oxidation organischer Verbindungen ist eines der fundamentalsten Probleme der modernen organischen Chemie. Effektive Lösungen müssen die spezifische Reaktivität und Selektivität von molekularem Sauerstoff berücksichtigen und unterschiedliche Klassen von Oxidationsreaktionen abdecken. Die…