Materials Literature
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Eine Pyrroleinheit eines Porphyrins als intramolekularer Protonendonor : Verbindung 1 (Strukturbild unten) mit einem deprotonierten Pyrrolring kann bei der oxidativen Umwandlung des entsprechenden luftempfindlichen 21‐Telluraporphyrins in das 21‐Oxaporphyrin als Intermediat isoliert werden. magnified image
In hohen Enantiomerenüberschüssen lassen sich nach dem hier vorgestellten Verfahren meso ‐1,4‐Endiolether wie 1 mit einem chiralen Rh I ‐Katalysator in Oxyketone 2 umwandeln, die als chirale Synthesebausteine von Interesse sind. TBS = tert ‐Butyldimethylsilyl. magnified image
We present in this paper a thermostatistical model of formation of vitreous B 2 O 3 which is based on a description of agglomeration of BO 3 triangles resulting in medium-range clusters and on the construction of the partition function related to the space of all possible pathways leading to this set of clusters. With…
Lead magnesium tungstate Pb 2 MgWO 6 undergoes a structural phase transition at about 310 K. This phase transition has been characterized by Raman spectroscopy. The main features of the Raman spectra, collected between 173 and 523 K, are consistent with group theoretical predictions though unexpected weak and broad si…
Exceptionally high binding constants Ka of up to 57000 have been determined for the binding of paraquat and polymeric paraquat derivatives 2 in the cavities of basket-shaped host molecules 1. Host–guest complexations of this kind are of interest with respect to the modification of the physical properties of electroact…
Transamination of the amidosamarium complex [{(Me3Si)2N}2Sm(tmeda)] with octaethylporphyrinogen (OEPG-H4) gives the dinuclear complex [(OEPG)Sm2(Et2O)2], which has two SmII centers and a short Sm–Sm contact. (In the structure shown on the right the Et2O ligands are omitted for clarity.)
On the basis of a quantitative fatigue model, various methods to minimize fatigue in oxide ferroelectric films are discussed. The model attributes fatigue to domain pinning by space charge that is caused by oxygen vacancy entrapment at the interfaces (e.g., electrode-ferroelectric, domain boundaries, etc.). Based on t…
Until now, elemental sulfur`s physical properties have not been systematically correlated. Simple tools for predicting these properties are necessary, especially for engineering calculations, because sulfur is widely used industrially. Newly developed correlations use temperature to estimate sulfur`s density, specific…
The room temperature current/voltage (I–V) characteristics of several porous silicon(PS)/metal diodes are measured. Different metals are used to form the contacts. Severe stress is also applied to the diodes and the I–V characteristics of stressed diodes are analysed. The present study supports the description of Ben…
The present work reports a successful solution to the problem of diamond deposition onto steel. This was achieved through the use of an intermediate layer between the substrate and the deposited film. The intermediate layer consisted of a 10 μm thick nitridized chromium film. The chromium film was produced by electroc…
Energy storage and release in dielectric materials can be described on the basis of the charge trapping mechanism. Most phenomenological aspects have been recently rationalized in terms of the space charge model~\cite{blaise,blaise1}. Dynamical aspects are studied here by performing Molecular Dynamics simulations. We…
The size dependence of the energy band gap for hydrogen saturated silicon clusters, wires and slabs are calculated using all electron density functional theory. The hydrogen saturation is considered as a model for a wider band gap insulator enclosing the silicon structures. With this perspective in mind, an effective…
Complex clusters the size of small proteins can be generated in reduced molybdate solutions by linking defined fragments. An example of this is the giant cluster (NH 4 ) 25±5 [Mo 154 (NO) 14 O 420 (OH) 28 (H 2 O) 70 ]·ca. 350 H 2 O with a molar mass of more than 30000 gmol −1 , the anion of which is shaped like a tire…
A two-dimensional electron system is expected to form a Wigner lattice at zero temperature but at very high electron densities even at T=0 one expects a phase transition from a crystal to a gas phase. For a Wigner lattice on a dielectric layer, a T=0 melting was also predicted at very low electron densities. Here we e…
The different allotropic forms of boron nitride have been investigated by $^{11}\mathrm{B}$ NMR and spin-lattice relaxation measurements. In the material with hexagonal symmetry the central transition is broadened by second-order quadrupole perturbation and the related quadrupole frequency ${\ensuremath{\nu}}_{\mathit…
The resistance of planar barriers is discussed for a variety of situations in which different sources of scattering act incoherently, allowing a semiclassical approach. This includes single barriers, a sequence of identical parallel barriers, and identical barriers at random angles simulating grain boundaries. Existin…
Third-order nonlinear-optical-susceptibility spectra \ensuremath{\Vert}${\mathrm{\ensuremath{\chi}}}^{(3)}$(-3\ensuremath{\omega};\ensuremath{\omega},\ensuremath{\omega},\ensuremath{\omega})\ensuremath{\Vert} have been obtained for free-standing porous silicon films by third-harmonic-generation (THG) measurements in a…
Effect of impurities on the high-field magnetization process in a frustrated antiferromagnet CuFeO 2 is studied for powder samples of CuFe 1- x Al x O 2 (0≤ x ≤0.1) and CuFe 1- x Cr x O 2 (0≤ x ≤0.08) using a pulse magnet up to 38 T. For the pure Fe compound distinct magnetization anomalies are successively observed a…
The free surface of a homologous series of low molecular weight liquid crystals 4-cyano-4′-n-alkyl-biphenyls (nCB, n=5,6,7,8) is studied by reflection ellipsometry. On approaching the bulk isotropic–nematic transition temperature TNI from the isotropic phase, the growth of a nematic layer at the surface is observed. T…
The defects of the Si(001)-${\mathrm{SiO}}_{2}$ interface have been studied by the electron-paramagnetic-resonance (EPR) technique taking advantage of the high specific surface area of porous silicon. This interface is characterized by the presence of two interface defects ${\mathit{P}}_{\mathit{b}0}$ and ${\mathit{P}…