Bondlengths of nearest neighbours around the Cu and Nb atoms in a Cuo.5NbS2 single crystal are extracted from the extended X-ray absorption fine structure (EXAFS) and lattice parameters are measured by X-ray diffraction. It is found that the Cu atoms occupy tetrahedral sites in the Van der Wads gap. Upon intercalation the NbS, sandwiches are squeezed by 0.009 nm whereas the van der Waals gap expands by 0.067 nm. The Nb-Nb distance in the NbS, layers increases by 0.003 nm. The Nb-S bond length shortens by 0.001 nm. The positions of the K-edge energies indicate a charge transfer from the Cu atoms to the host sandwich layers.Bindungslangen zu nachsten Nachbarn um die Cu-und Nb-Atome in einem Cuo,5NbS2-EinkristaIl werden aus der kantenfernen Rontgenabsorptionsfeinstruktur (EXAFS) ermittelt und die Gitt,erkonstanten werden mittels Rontgenbeugung gemessen. Es wird festgestellt, da13 die Cu-Atome Tetraederlucken in der Van-der-Waals-Liicke besetzen. Durch clie Interkalation werden die NbS,-Schichten um 0,009 nm ZusammengepreIJt,, wahrend sich die van-der-~~aa.ls-Licke urn 0,067 nm aufweitet. Der Nb-Nb-Absta.nd in den NbS,-Schichten wird nm 0,003 nm gro13er. Die Nb-S Bindungslange wird um 0,001 nm lriirzer. Die energetischen Lagen der K-Kanten weisen auf einen Ladungst.ransfer von den Cu-Atomen zu den Schichten des Wirtskrist,alls hin.

No abstract

A new wavelength tunable laser diode with a basically continuous tuning behavior is presented. This essential progress is achieved by transversely tuning the effective index of a distributed feedback laser using a twin waveguide. Due to the built-in synchronization of the Bragg wavelength and the optical cavity length, the wavelength is controlled by only a single current. The device technology and preliminary experimental results demonstrating the transverse tuning mechanism are presented.

No abstract

A laboratory spectrometer for x-ray absorption measurements is described which is adaptable to changing experimental requirements. The spectrometer is designed for the use of different types of curved crystals within large ranges of radii of curvature and of Bragg angles. Utilizing a 12-kVA rotating anode x-ray generator, Johansson-type monochromator crystals, and a helium-flow flexible beam line, photon fluxes between 105 and 107 photon/s are achieved in the photon energy range between 5 and 20 keV, where the energy resolution varies between 2 and 10 eV.