Lattice sites of Li in Si and Ge

The lattice sites of ion implanted Li-8 in Si and Ge were studied using the alpha-emission channeling technique. In both materials tetrahedral interstitial sites were found to be the major occupied lattice sites following room temperature implantation (60-80% in Si and 40-60% in Gel. Depending on the doping character of the sample, up to 55% of Li was found on bond-center sites in Si after implantations between 425 K and 475 K and up to 40% in Ge for implantations between 325 K and 400 K at higher temperatures Li occupied increasingly random lattice sites. The lattice site changes from tetrahedral to bond-center sites are attributed to the onset of interstitial Li diffusion and its capture by additional defects, which are likely to be vacancy-type defects from the implantation process. The trapping of Li at these defects inhibits its long-range diffusion

Erbium related centers in CZ-silicon

CZ Si implanted with Er shows the same cubic crystal field splitting of the 1.54 mu m luminescence as FZ-SI together with otter, defect- and oxygen correlated Pr complexes. The cubic centers exhibit somewhat shorter radiative life- and excitation times. The 100 times higher luminescence yield of CZ samples is thus attributed to the improved incorporation and to the passivation of recombination centers. The latter conclusion is supported by DLTS results which indicate complicated annealing behaviour

ELECTRONIC-STRUCTURE OF LA2-XSRXNIO4 STUDIED BY PHOTOEMISSION AND INVERSE-PHOTOEMISSION SPECTROSCOPY

The electronic structure of La2-xSrxNiO4 is studied by use of photoemission spectroscopy, bremsstrahlung-isochromat spectroscopy (BIS), and electron-energy-loss spectroscopy. Quantitative analyses are made on the valence-band and Ni 2p core-level photoemission spectra through configuration-interaction calculations on a NiO6 cluster model. On the basis of these analyses, it is concluded that La2NiO4 is a charge-transfer (CT) insulator and the magnitude of the band gap is about 4 eV, nearly the same as that of NiO. The BIS spectra show that unoccupied states induced by hole doping are spread over the CT gap, which is incompatible with a rigid-band picture for the hole doping. We discuss the origin of the different insulator-to-metal transition behavior between this system and La2-xSrxCuO4

Evidence for correlation effects in Sr2RuO4 from resonant and x-ray photoemission spectroscopy

We study the electronic structure of Sr2RuO4, a noncuprate layered superconductor (T-c=0.93 K), using electron spectroscopy. X-ray photoemission spectroscopy shows that the single particle occupied density of states (DOS) is in fair agreement with the calculated DOS. However, resonant photoemission spectroscopy across the Ru 4p-4d threshold establishes the existence of a correlation satellite to the Ru 4d band. The results indicate substantial charge-transfer character at the Fermi level, with on-site correlations U-dd comparable in magnitude to the Ru-O hopping integral, like the cuprates

Symmetry of the 3d9 Ligand Hole Induced By Doping In Yba2cu3o7-delta

Polarized Cu L3-edge x-ray absorption spectra of a single crystal of YBa2Cu3O6.8 have been measured to determine the symmetry of the orbital of the electronic holes induced by doping. The states induced by doping in YBa2Cu3O7-δ (0<δ<~0.5) have been found to be ligand holes L*, giving the 3d9L* configuration, and their weight is correlated with Tc. The polarization dependence shows that the hole L*, induced by doping, is found to be mainly in the Cu-O orbital oriented along the c axis involving the O 2pz orbital of & orbitals. This result indicates the important role of BaO layers and shows that theories of high-Tc superconductivity have to take account of a second band with different symmetry, beyond the single band (the two-dimensional band & and O 2px,2py orbitals in the a-b plane of the CuO2 layers) usually considered in models of the electronic structure of high-Tc superconductors