Materials Literature
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Abstract Der Sehvorgang sowie andere durch Licht ausgelöste biochemische Umsetzungen in Pflanzen und Lebewesen sind ausgeklügelte biologische Vorgänge, in denen optische Signale registriert und in (physiko)chemische umgesetzt werden. Photoschaltbare Biomakromoleküle sind eine neue Klasse von Substanzen, in denen optis…
Electrochromic vanadium pentoxide (V2O5) thin films are prepared by the physical vapour deposition method using an electron beam gun. The transmission spectra of V2O5 thin films are measured and studied before and after UV irradiation. It is observed that the optical transmission minimum which occurs at 320 nm does no…
Multidimensional potential energy surfaces for systems larger than about 15 atoms are so complex that interpreting their topographies and the consequent dynamics requires statistical analyses of their minima and saddles. Sequences of minimum-saddle-minimum points provide a characterization of such surfaces. Two exampl…
Current research into semiconductor clusters is focused on the properties of quantum dots—fragments of semiconductor consisting of hundreds to many thousands of atoms—with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly s…
The crystal structure of [Mn(TPP)Cl] in space group I4/m (where TPP is C44H28N4) has been determined. The unit cell contains two full molecules, with one eighth of a molecule unique. An out-of-plane model for the Mn atom was applied and all non-H atoms were refined anisotropically. The Mn--N distance is 2.002 (3) A, t…
The electronic structure of ${\mathrm{Ag}}_{2+\ensuremath{\delta}}\mathrm{S}$ single crystals is investigated as a function of temperature and nonstoichiometry, $\ensuremath{\delta}$. It is shown that the stoichiometric, low-temperature $\ensuremath{\alpha}$-${\mathrm{Ag}}_{2}$S phase is a band insulator with correlat…
We studied electro-optical properties of 5–13-μm-thick films of a short pitch (0.43 μm) chiral smectic C liquid crystal in bookshelf structure. The anchoring at the silane treated surfaces was relatively weak so that the relaxed bookshelf structure was helical also at the surfaces. Low fields cause only a deformation…
The synthesis of macrocycle-containing liquid crystals is reviewed with particular emphasis on derivatives of synthetic aza crowns. The synthesis of the C-functionalized thioether crowns (HO)$_{2}$[14]aneS$_{4}$ and (HO)$_{2}$[16]aneS$_{4}$ is described, and their derivatization to give oligobenzoate esters discussed.…
Using Möller–Plesset second-order perturbation theory (MP2) for the geometry optimizations, we have examined various structural possibilities for the Si4C cluster. The energies of the MP2-optimized structures have been calculated using singles and doubles coupled cluster (CCSD) theory and the CCSD (T) method. The stru…
Hydrogen absorption by 200--2000-\AA{}-thick Pd-capped Nb films, between 5 and 110 \ifmmode^\circ\else\textdegree\fi{}C, was studied by simultaneous four-probe resistivity and volumetric measurements. The resistivity as a function of hydrogen concentration was measured while charging the films with hydrogen, and was u…
The structure of tin(II) oxyhydroxide, Sn6O4(OH)4, has been refined by Rietveld analysis of X-ray powder diffraction data. Atomic parameters based on the isostructural lead analogue were used in the starting model. The structure was refined in the tetragonal space group P\overline{4}21c with a = 7.9268 (4) and c = 9.1…
A comparative study has been made of the structures and magnetic properties of Nd10Fe84B6 prepared by mechanical alloying using elemental powders as starting materials and by mechanical milling of the alloy. Both milling procedures resulted in a mixture of α-Fe and an amorphous phase, with the fraction of α-Fe phase b…
Porous silicon presents a fascinating pore morphology, which could be relevant for its efficient luminescent properties in the visible spectrum. This work attempts to give some insight into the understanding of its optical properties, by studying the electronic band structure. The porous structure is modeled as empty…
A deconvolution formula has been derived for the background subtraction of electron spectra by including the effect of surface excitations into the Landau formula. With this formula the primary x-ray photoelectron spectroscopy spectra of Cu, Ag, and Au are calculated from the experimental data. The primary excitation…
Waveguided Raman measurements have been performed in order to detect the presence of Ag nanoclusters in soda-lime glass waveguides obtained by ion exchange. By subtracting a strong broadband luminescence and the Raman contribution of the glass matrix, a low frequency Raman peak is resolved. The peak is ascribed to sur…
A simple model of electron kinetics, previously used in molecular and protein electron dynamics, is applied to transport and photoluminescence in wet and dry porous Si. Porous Si is modeled as a system of touching Si nanocrystals that individually show strong three-dimensional confinement. In the presence of a polar l…
A hyper-Rayleigh scattering (HRS) system based on an optical parametric power oscillator is described. The first hyperpolarizability, beta, of Crystal Violet dye was measured at 1450 and 1500 nm. The resonance-free beta value, beta(0), for this octupole was found to be comparable with that of the dipolar dye Disperse…
We present a non-self-consistent density-functional based construction of nonorthogonal tight-binding (TB) matrix elements for B, N, BN, BH, and NH within the framework of the linear combination of atomic orbitals formalism using the local-density approximation. Despite the simplicity of the scheme considering only tw…
Energy-filtered electron imaging is one of the future directions of high-resolution electron microscopy (HREM). In this paper, characteristics and applications of energy-selected HREM are illustrated. Image contrast can be dramatically improved with the use of an energy filter. High-resolution chemical-sensitive imagi…
Single-crystal Ce films of more than 300 \AA{} thickness have been epitaxially grown on W(110). Their interaction with molecular oxygen at room temperature has been studied by angle-resolved photoemission, low-energy electron diffraction, and Auger spectroscopy. As a function of the oxygen exposure, the reaction is fo…