Bulk ZnO samples, epitaxially grown ZnO layers, and ZnO nanostructures frequently exhibit a characteristic emission band at 3.31-eV photon energy whose origin is controversially discussed in the literature. Partly, this omnipresent band is ascribed to ͑e , A 0 ͒ transitions of conduction band electrons to acceptors, which are abundant in relatively high concentrations but have not positively been identified. The band is, in particular, often reported after intentional p-type doping of ZnO, preferentially with group V species. In the present work, we study the 3.31-eV band by low-temperature cathodoluminescence ͑CL͒ with high spatial resolution, by scanning electron microscopy, and by transmission electron microscopy ͑TEM͒. Line shape analyses at different temperatures give clear evidence that the band originates from an ͑e , A 0 ͒ transition where the acceptor binding energy is ͑130Ϯ 3͒ meV. The 3.31-eV luminescence is exclusively emitted from distinct lines on sample surfaces and cross sections representing intersections with basal planes of the wurtzite hexagons. Correlating monochromatic CL images with TEM images, we conclude that the localized acceptor states causing the 3.31-eV luminescence are located in basal plane stacking faults.

No abstract

Cathodoluminescence spectra recorded with high spatial and wavelength resolution on tilted ZnO epitaxial layers allow to identify a very prominent emission peak at 3.314 eV as a free electron to shallow acceptor (E A % 130 meV) transition. By correlation with TEM cross-section images recorded on the same samples we can find these acceptor states to be located on basal plane stacking faults (BSFs). Locally, high concentrations of acceptor states are found. Since this spectral feature is often reported in literature especially after attempts to obtain p-type or transition metal doping, we conclude that stacking faults are a common by-product when group V or other extrinsic atoms are incorporated in ZnO layers or nanostructures.

A simple and efficient synthesis and characterization of a series of first generation dendrimers based on cyclophosphazene cores and containing up to 16 peripheral chiral ferrocenyl ligands is described.

No abstract

No abstract

No abstract

Key words ultrathin NbN films, hot-electron bolometers, microstructure, transmission electron microscopy. PACS 68.37.Lp Structural, chemical and superconducting properties of thin NbN films used for development of fast and sensitive hot-electron bolometer (HEB) detectors for wide spectra range are reported. The thin NbN films with a thickness between 4 and 10 nm were deposited on the (001)Si substrates by magnetron sputtering. In order to investigate the film morphology and microchemistry, diffraction-contrast and high-resolution transmission electron microscopy (TEM) in combination with scanning TEM and electron energy loss spectroscopy (EELS) were performed. In addition, the zero-resistance critical temperature of the NbN films was measured and correlated to their thickness. The interrelations between fabrication conditions, crystalline and superconducting properties of the differently thick NbN films are discussed. Dedicated to Prof. Wolfgang Neumann on the occasion of his 65th birthday