Orientation Control of Standing Epitaxial Pentacene Monolayers Using Surface Steps and In-plane Band Dispersion Analysis by Angle Resolved Photoelectron Spectroscopy

ABSTRACTWe prepared quasi single crystalline pentacene monolayer films on Bi-terminated Si(111) by using bunched steps on vicinally-cut surfaces as an orientation template. Band dispersion in the conduction plane of pentacene was clearly observed by angle-resolved photoelectron spectroscopy.

HIGH-TEMPERATURE SUPERCONDUCTIVITY CAUSED BY CIRCULAR POLARIZED ZERO-POINT OSCILLATION

A new model is proposed on the recently found non-cuprate high temperature superconductivity in crystal with 2D conduction plane which is composed of the planar connection of many circular localized orbits. Our findings are as follows: (i) the ground state of the doped 2D particle system in zero point oscillation is similar to the particle state in very strong magnetic field, (ii) Laughlin state with filling factor ν = 1/2 is the most stable state of the 2D particle system, (iii) the superposition of many fluctuating Laughlin states in pure crystal gives a coherent state with superfluidity. (iv) This model gives an estimation of the upper limit of the superconductivity transition temperature: [Formula: see text] for fcc C 60, and [Formula: see text] for Ag β Pb 6 CO 9, which are close to observation.

Next-near-neighbour interactions with Al in Li+- and Rb+-exchanged Na+β-aluminas, detected by synchrotron X-ray absorption spectroscopy

Synchrotron X-ray absorption near-edge structure (XANES) spectroscopy studies have been carried out on the electronic and crystal structure environments around the Al atom in Na+β-alumina and in two β-aluminas with Na+exchanged by Li+and Rb+. The aim is to define the type of interaction, if any, existing between the Al located in the `spinel block' and the fast-conducting cations in the `conduction plane'. Na+β′′-alumina has also been studied for comparison. All β-alumina spectra differ from that of α-alumina (corundum) by showing additional features due to the presence of tetrahedral Al. Moreover, they all show a much greater degree of local disorder. There are definite, but small, interactions between tetrahedral Al (and, possibly, also octahedral Al) in the `spinel block' and the Na+and Rb+cations in the `conduction plane'; Na+and Rb+β-aluminas have similar AlK-edge XANES features, but with intensities that change in relation to the weight of the `conduction plane' atom. Despite differences in composition and structure, Na+β′′-alumina shows the same behaviour, thus confirming the substantial similarity of the Al local environments. Li+-exchanged β-alumina has an AlK-edge XANES spectrum that apparently differs from all others, but actually conveys the same basic information. Indeed, interaction between Al and Li is much greater than in any other β-alumina because Li+moves laterally off the `conduction plane' to become close to a facing tetrahedral Al, and strongly interacts with it. Thus, this study also draws attention to the fact that β-aluminas react differently to alkali exchange.

Transport Properties And Crystal Chemistry Of Ba-Sr-Bi Oxides

ABSTRACTRhombohedral (R) phases of the binary systems AE-Bi-O (AE = Ca, Sr, Ba) have low temperature (β2) and high temperature (β1) polymorphs and the β1 polymorph is a good oxygen ion conductor. In a previous study, we showed that in the ternary system Ba-Sr-Bi-O, conductivities of polycrystalline R samples are unaffected by Ba:Sr, whereas temperature ranges of the β2↔β1 polymorphic transition are. Recently, we proved that the conductivity of both polycrystalline and single-crystal R samples is sensitive to spatial direction. For single crystals, the conductivity is highest perpendicular to the c-axis. Along the conduction plane, the conductivities are significantly higher than those of polycrystalline R samples; perpendicular to that plane they are significantly lower. The BaBiO3 perovskite (P) phase, predominantly an electronic conductor, has conductivities of 10 to 102 S/cm at 350-800°C in air. Conductivity measurements of the R-P assemblages with different R:P showed that percolation threshold is around 35 volume % P.

Li+/Na+ β-Alumina: A Combined Single-Crystal Neutron and X-ray Diffraction Study

The crystal structure and ionic distribution in the conduction plane of the partially exchanged Na+ \beta-alumina system Li0.75Na0.47Al11O17.11 has been determined from single-crystal X-ray diffraction at 30 and 298 K, in combination with a single-crystal neutron diffraction study at 295 K. At 30 K the Li+ ions occupy two sites: one in (2/3, 1/3, 1/4) and one ∼1.0 Å out of the z = 1/4 conduction plane. The Na+ ions are also found in two sites, both in the conduction plane. At 298 K the Li+ ions are found in three sites; the same two sites as at 30 K, as well as at a third site between these two. The Na+ ions occupy the same sites as at 30 K. The combination of X-ray and neutron diffraction is used to resolve the distribution of Na+ and Li+ ions. The column O5 atom in the Al3—O5—Al3 bridge between the spinel blocks is found to be disordered. Charge compensation is achieved through a Frenkel defect of two interstitial Al atoms, one on either side of the conduction plane, together with an extra oxygen in the conduction plane. One such defect occurs, on average, in every 4.5 unit cells.

Ionic Distribution in Rare Earth Ion-Doped Na+ β"- Alumina

Structure of β"-alumina has been studied through atomistic simulation. Distribution of Mg2+ in the spinel blocks, Na+ as well as Nd3+ in the conduction planes have been calculated and compared with the structure models derived experimentally. Mg2+ ions, as the stabilizer of β"-alumina structure, prefer to occupy the tetrahedral Al(2) sites in the spinel block. Two configurations for Mg2+ distribution are proposed. Due to the presence of Mg2+, oxygen ions in or adjacent to the conduction plane, O(5), O(4) and O(3), are slightly displaced from their original sites, leading to the removal of the local symmetry at the mO site. Strongly affected by the Mg2+ distribution, Nd3+ions, originally introduced into the BR site in the conduction plane, are found to move towards the distorted mid-oxygen sites, which is in excellent agreement with the previous estimate from spectroscopie study.

TOPOGRAPHICAL FEATURE OF HIGH JcYBa2Cu3Ox SUPERCONDUCTOR

Melt-textured growth of polycrystalline YBa 2 Cu 3 O x superconductor using directional solidification created a compact texture consisting of large plate-shaped crystals aligned preferentially parallel to the a – b conduction plane and many ordered parallel growth steps perpendicular to the growth direction of the YBa 2 Cu 3 O x crystal. The new microstructure, which completely substitutes the previous granular and random structure in the sintered bulk materials, exhibits significantly enhanced transport J c values of 23800 A/cm 2 at 77 K and in a H = 2 Tesla field.

RAMAN SCATTERING STUDY OF Ag+-IMPLANTED β-ALUMINA CRYSTALS

We have measured Raman spectra of sample of sodium β-alumina and samples with silver ion implantation where one kind of sample was not annealed after the implantation, and the others were Ag +-implanted with annealing for 30 minutes at 300, 400, 500 and 700°C, respectively. Raman spectra show that silver ion implantation disturbs sublattice of Na + in β-alumina with some disorder features and some resonance modes appeared in the Raman spectra. We have found the critical annealing temperature near 400°C, above which the silver ion, typically with small activation energy 0.18 eV, gains enough energy to diffuse rapidly through the vacancy clusters formed by silver ion implantation and also through the conduction plane of crystal between clusters in β-alumina with high ionic conductivity.