Morphological,structural and electrical investigations on non-polar a-plane ZnO epilayers

We report on the growth of non-polar a-plane ZnO by CVD on r-plane-sapphire-wafers, a-plane GaN-templates and a-plane ZnO single-crystal substrates. Only the homoepitaxial growth approach leads to a Frank–van-der–Merwe growth mode, as shown by atomic force microscopy. The X-ray-diffraction spectra of the homoepitaxial thin films mirror the excellent crystalline quality of the ZnO substrate. The morphological and the structural quality of the homoepitaxial films is comparable to the best results for the growth on c-plane ZnO-substrates. The impurity incorporation, especially of group III elements, seems to be reduced when growing on the non-polar a-plane surface compared to the c-plane films as demonstrated by secondary ion mass spectrometry (SIMS). Optical properties have been investigated using low temperature photoluminescence measurements. We employed capacitance–voltage measurements (C–V) to measure the background carrier density and its profile from substrate/film interface throughout the film to the surface. In thermal admittance spectroscopy (TAS) specific traps could be distinguished, and their thermal activation energies and capture cross sections could be determined.     

Microactuators based on conducting polymers

In this contribution we report the use of polyaniline and polypyrrole for miniaturized actuators fabricated by microstructural and electrochemical technologies. The potential necessary to drive the actuator is typically less than 1 V, i.e. 2-3 orders of magnitude lower than that necessary for the widespread piezoelectric actuator devices. This low voltage is imperative for future application of actuators of micrometer dimensions. The volume variation of polymers substantially exceeds that of piezoelectric materials. Different contributions to the actuator characteristics are discussed and evaluated semi-quantitatively.     

On the mechanism of the144Nd(p, α)141Pr reaction

Zeitschrift für Physik A Hadrons and nuclei - Experimental evidence is presented that the144Nd(p, α)141Pr reaction excites residual nucleus levels with a dominant single proton...     

On the microwave conductivity of α-AgI. part II: Complex conductivity by measurement of the complex transmission factor

The electrical conductivity and the dielectric constant of α-AgI are computed in the frequency region from 8.2 to 40 GHz from the complex transmission factor of polycrystalline samples, which totally fill the crossection of a rectangular waveguide. No frequency dependence of both the conductivity and the permittivity is found in the entire temperature range studied (400 K to 720 K). The high frequency values coincide with the static ones.     

Ferrocenes with perfluorinated side chains and ferrocenophanes with fluorinated handles

Trifluorovinyl groups are introduced onto the cyclopentadienyl ligands of ferrocene at the 1-, 1,1'-, and 1,2-positions by Negishi-type and Stille-type coupling reactions of trifluorovinylzinc chloride and tri-n-butyltrifluorovinyl stannane with several iodoferrocenes. Modification of the trifluorovinyl group by nucleophilic substitution and [2+2] cycloaddition make them versatile building blocks for synthetic transformations. 1,1'-Bis(trifluorovinyl) ferrocene reacts upon contact with silica or oxidizing agents and in the presence of a suitable nucleophile through a redox autocatalytic mechanism to afford ferrocenophanes with fluorinated handles. C(F)(H) and C(F)(OMe) moieties in α-positions allowed further modifications to be performed by nucleophilic substitution of the fluorine atoms. A series of ferrocenes with fluorinated side chains and ferrocenophanes with fluorinated handles were isolated and characterized. Several molecular structures were determined by single-crystal X-ray diffraction. The influence of the fluorine substituents on the redox properties of the iron center were studied by cyclic voltammetry.