Observation and destruction of an elusive adsorbate with STM: O₂/TiO₂(110)

When a slightly defective rutile TiO?(110) surface is exposed to O?at elevated temperatures, the molecule dissociates at defects, filling O vacancies (V(O)) and creating O adatoms (O(ad)) on Ti(5c) rows. The adsorption of molecular O? at low temperatures has remained controversial. Low-temperature scanning tunneling microscopy of O?, dosed on TiO?(110) at a sample temperature of ≈100 K and imaged at 17 K, shows a molecular precursor at V(O) as a faint change in contrast. The adsorbed O? easily dissociates during the STM measurements, and the formation of O(ad)'s at both sides of the original V(O) is observed.     

Chaotic inflation in supergravity with Heisenberg symmetry

We propose the introduction of a Heisenberg symmetry of the Kähler potential to solve the problems with chaotic inflation in supergravity, as a viable alternative to the use of shift symmetry. The slope of the inflaton potential emerges from a small Heisenberg symmetry breaking term in the superpotential. The modulus field of the Heisenberg symmetry is stabilized and made heavy with the help of the large vacuum energy density during inflation. The observable predictions are indistinguishable from those of typical chaotic inflation models, however the form of the inflationary superpotential considered here may be interpreted in terms of sneutrino inflation arising from certain classes of string theory.     

Mössbauer phase analysis of a welding interface

Changes in the distribution of alloying elements and phase composition in the surroundings of the welding interface of two martensitic steels were studied by means of Conversion Electron Mössbauer Spectroscopy. It is shown that the redistribution of carbon due to its difference in chemical potentials in the individual steels is accompanied by fine changes in the phase composition detected.     

Non-ohmic behaviour of iodine-doped polyacetylene

We report on the temperature and electric field strength dependence of the conductivity of iodine-doped polyacetylene in the metallic regime. The experimental results are discussed in terms of Sheng model of fluctuation induced tunneling and characteristic dimensions of the tunneling zones between fibres are deduced from a fit between this theory and our experiments.     

Signature of a type-a glass transition and intrinsic confinement effects in a binary glass-forming system

We study dynamically highly asymmetric binary mixtures comprised of small methyl tetrahydrofuran (MTHF) molecules and polystyrene. Combined use of dielectric spectroscopy, ^{2}H nuclear magnetic resonance, incoherent quasielastic neutron scattering, and depolarized dynamic light scattering allows us to selectively probe the dynamics of the components in a broad dynamic range. It turns out that the mixtures exhibit two glass transitions in a wide concentration range although being fully miscible on a macroscopic scale. In between both glass transition temperatures, the dynamics of the small molecules show strong confinement effects, e.g., a crossover from Vogel-Fulcher to Arrhenius behavior of the time constants. Moreover, the dynamical behavior of small molecules close to the slow matrix is consistent with mode coupling theory predictions for a type-A glass transition, which was expected from recent theoretical and simulation studies in comparable systems.