Dominik Wrana

Dynamics of thermally induced assembly of Au nanoislands from a thin Au layer on Ge(001)

The dynamics of morphology changes upon post-deposition annealing of a thin film of 6 ML Au deposited on a (2 × 1) reconstructed Ge(001) surface was studied in a systematic way by scanning electron and atomic force microscopy. It has been found that annealing of the initial, continuous Au layer leads to the development of nanoislands which are crystalline and epitaxial to the Ge(001) substrate surface. The nanoislands formed at annealing temperatures lower than the bulk eutectic temperature for the Au–Ge system (634 K) are rectangular, with a flat top, while the nanoislands developed by annealing at temperatures higher than the bulk eutectic temperature have more complex, octagonal shapes. Moreover, the octagonal Au nanoislands are nearly half-buried in the Ge substrate and surrounded by a crystalline Ge rim.

Electrical nanopatterning of TiO2 single crystal surfaces in situ via local resistance and potential switching

The resistive switching effect in transition metal oxides allows for a dedicated manipulation of the oxide resistance via electrical stimuli. Here, we perform local-conductivity atomic force microscopy simultaneously with the Kelvin probe force microscopy under ultra-high vacuum conditions using the very same tip investigating the very same sample area to monitor the surface conductivity and surface potential of thermally reduced TiO2 single crystals. We show that the resistance of confined surface areas can be switched by applying a voltage of several volts to the tip during scanning in the contact mode. By conducting in situ oxidation experiments, we present that this surface switching is related to a local redox reaction, which can be controlled electrically allowing for surface nanopatterning and illustrates the capability of transition metal oxides for multilevel resistive switching being a prerequisite for neuromorphic computing. We discuss that the features of the electrically engraved nanopattern can be scaled down to a lower boundary at several tens of nanometers. The observed limit around 25 nm is determined by the presence of intrinsic local variations in electrical surface properties appearing as a common phenomenon of slightly reduced metal oxide surfaces.The resistive switching effect in transition metal oxides allows for a dedicated manipulation of the oxide resistance via electrical stimuli. Here, we perform local-conductivity atomic force microscopy simultaneously with the Kelvin probe force microscopy under ultra-high vacuum conditions using the very same tip investigating the very same sample area to monitor the surface conductivity and surface potential of thermally reduced TiO2 single crystals. We show that the resistance of confined surface areas can be switched by applying a voltage of several volts to the tip during scanning in the contact mode. By conducting in situ oxidation experiments, we present that this surface switching is related to a local redox reaction, which can be controlled electrically allowing for surface nanopatterning and illustrates the capability of transition metal oxides for multilevel resistive switching being a p...