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A3: Atomic structure and local spectroscopy of complex oxidic structures

The experimental determination of the atomic structure of oxide interfaces and their specific interface-induced electronic, dielectric and/or ferroelectric properties are the strategic aspect of the project A3. The central methods to reach this goal are scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), atomic force microscopy (AFM) and piezo-response force microscopy (PFM). In the ongoing funding period, the focus will be on the atomic and electronic properties of the recently discovered two-dimensional oxide quasicrystals (OQC). For the dodecagonal barium titanate-derived layer on Pt(111), the structural formation process and the local bonding concepts that lead to the unusual aperiodic long-range order are unknown. The combination of the experimental methods of STM, STS, and AFM with photoelectron spectroscopy and microscopy (PEEM) should enable a broader access to these issues. The identification of two long-range ordered approximant structures for this system allows the direct comparison of aperiodic and periodic oxide structures. These investigations should lead to new concepts for the structural and electronic properties of two-dimensional quasicrystals. At the same time, the project searches for other oxide quasicrystals starting from thin films of oxide perovskites on metal substrates with threefold symmetry. This might lead to the general concept of OQCs.

In a second work package, the ferroelectric and multiferroic domain structures of ultrathin oxide films are investigated by STM, PFM and PEEM. Here the interface-induced stabilization of domains on metallic and magnetic substrates is the main focus with emphasis on the details of the ferroic coupling.

Principal Investigator

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