Graphene on Rh(111): STM and AFM studies

The electronic and crystallographic structure of the graphene/Rh(111) moir\'e lattice is studied via combination of density-functional theory calculations and scanning tunneling and atomic force microscopy (STM and AFM). Whereas the principal contrast between hills and valleys observed in STM does not depend on the sign of applied bias voltage, the contrast in atomically resolved AFM images strongly depends on the frequency shift of the oscillating AFM tip. The obtained results demonstrate the perspectives of application atomic force microscopy/spectroscopy for the probing of the chemical contrast at the surface.Comment: manuscript and supplementary information; submitted to Appl. Phys. Lett. on 01.03.201

Scanning tunneling and atomic force microscopies studies

The electronic and crystallographic structure of the graphene/Rh(111) moiré lattice is studied via combination of density-functional theory calculations and scanning tunneling and atomic force microscopy(STM and AFM). Whereas the principal contrast between hills and valleys observed in STM does not depend on the sign of applied bias voltage, the contrast in atomically resolved AFM images strongly depends on the frequency shift of the oscillating AFM tip. The obtained results demonstrate the perspectives of application atomic force microscopy/spectroscopy for the probing of the chemical contrast at the surface

Nonexponential relaxation dynamics of localized carrier densities in oxide crystals without structural or energetic disorder

A microscopic model for the nonexponential relaxation of localized charge carrier densities in oxide crystals is derived by taking into account thermally activated diffusive hopping transport and the effect of trap saturation. Thereby it is shown that the relaxation, commonly described by a stretched exponential function, can be successfully reconstructed without consideration of a structural or energetic disorder. Furthermore, the access to particular microscopic measures such as the lifetime of single hopping events and localized carrier densities is enabled. The impact of the model approach valid for various complex relaxation processes is demonstrated with the nonexponential relaxation dynamics of optically generated small bound polaron densities experimentally determined in KNbO3 as an exampl

Distinct Physicochemical Properties of the First Ceria Monolayer on Cu(111)

Discontinuous ceria layers on Cu(111) represent heterogeneous catalysts with notable activities in water-gas shift and CO oxidation reactions. Ultrathin ceria islands in these catalysts are composed of monolayers of ceria exhibiting CeO2(111) surface ordering and bulklike vertical stacking (O-Ce-O) down to a single ceria monolayer representing the oxide-metal interface. Scanning tunneling microscopy (STM) reveals marked differences in strain buildup and the structure of oxygen vacancies in this first ceria monolayer compared to thicker ceria layers on Cu(111). Ab-initio calculations allow us to trace back the distinct properties of the first ceria monolayer to pronounced finite size effects when the limiting thickness of the oxide monolayer and the proximity of metal substrate cause significant rearrangement of charges and oxygen vacancies compared to thicker and/or bulk ceria