Theory of Current and Shot Noise Spectroscopy in Single-Molecular Quantum Dots with Phonon Mode

Using the Keldysh nonequilibrium Green function technique, we study the current and shot noise spectroscopy of a single molecular quantum dot coupled to a local phonon mode. It is found that in the presence of electron-phonon coupling, in addition to the resonant peak associated with the single level of the dot, satellite peaks with the separation set by the frequency of phonon mode appear in the differential conductance. In the ``single level'' resonant tunneling region, the differential shot noise power exhibit two split peaks. However, only single peaks show up in the ``phonon assisted'' resonant-tunneling region. An experimental setup to test these predictions is also proposed.Comment: 5 pages, 3 eps figures embedde

Carrier transport in azomethine oligomers grown by multiple self-assembly

Applied Science

The surface of the perovskites LiBaF3 and BaZrO3 studied by low-energy ion scattering

Low‐energy ion scattering has been performed on the normal perovskite BaZrO3 and the only known inverse perovskite LiBaF3. BaO2, ZrO2, and BaF2 were used to quantify the surface coverage of the different constituents. In BaZrO3 the surface coverage showed an enrichment of Ba. Calibration to the metaloxides gave surface coverages of 80% and 20% for Ba and Zr, respectively. For the LiBaF3, also a higher Ba coverage was detected, and, compared to BaF2, found to be 75%. The enrichment of this twelvefold coordinated cation can be explained in terms of a segregation effect due to a lower surface free energy of the bariumoxide and ‐fluoride with respect to the zirconiumoxide or lithiumfluoride. In view of our earlier experiments on spinel structures, preferential exposure of certain planes of the perovskite structure is another possibility, which has yet to be evaluated. The results indicate that a surface terminated by cations in the B‐site, in most cases transition metals, does not present a reliable model when discussing the catalytic activity of the perovskites

Surface and bulk cation distribution of the spinel system ZnxMg1−xFe2O4

ZnxMg1-xFe2O4 mixed oxide spinels (x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) were prepared by conventional solid state reaction method. Bulk and surface characterization of these ferrites were carried out by different techniques. The ratios Zn/Fe and Mg/Fe determined by PIXE and AAS were nearly as expected from the synthesis mixture, i.e. following the substitution model. XRD shows only a spinel structure (fcc) with increasing lattice parameter as x increases from 0 to 1. The bulk ratios of tetrahedral to octahedral sites occupied by Fe cations measured by NGR are in good agreement with the theoretical bulk stoichiometry. LEIS results indicate a Mg substitution by Fe cations at the surface. Only octahedral sites are proposed at the surface. The transition from inverse to normal spinel was follow through NGR-spectra occurring at x=0.4