Surface structure and reactivity of
multi-component oxides at the atomic scale

Subproject P02

Multi-component metal oxides exhibit a plethora of stoichiometry-dependent structural phases at the surface, even if the composition of the bulk is kept the same. The long-term objective of P02 is to unravel the relationship between surface electronic and geometric structure and reactivity, to ultimately tune these materials for energy-related reactions such as the ORR. The project applies the surface science approach. We will grow well-defined, epitaxial perovskite thin films of LSFO and LSMO in a UHV-based PLD/surface science apparatus under tight control of the surface stoichiometry in the first project period. We will determine the coordinates of surface atoms quantitatively using LEED-IV in close collaboration with theoretical groups.

Theoretical models will also help with interpreting atomically-resolved ncAFM/STM images. These images give direct insights into the behavior of polarons in these complex materials and show how adsorbates such as O₂, H₂O, CO, and CO₂interact with electronic and structural defects. XPS, TPD, and FTIR of these well-defined systems will deliver desorption energies, vibrational frequencies, and spectral fingerprints. These experimental data on well-defined systems will build a bridge when tested under ‘realistic’ environments at high pressure/temperature and in aqueous solutions. They will also serve to validate ML-based theory approaches.

Ulrike Diebold
PI

Expertise

Our expertise is experimental surface science. We operate a total of seven ultrahigh-vacuum (UHV) chambers, which contain virtually all main experimental surface science techniques, as well as an (electro-)chemistry lab.

All chambers are equipped with facilities for sample preparation (sputtering/annealing/gas dosing), as well as various growth techniques (e-beam evaporators, Knudsen cells, UHV-compatible sputter deposition, pulsed laser deposition (PLD)).

Analysis techniques used in our research include:

Scanning Tunneling Microscopy (STM) (in UHV 4K – 300 K, electrochemical STM)
Atomic Force Microscopy (AFM): UHV-based (q+ sensor) and in the ambient (cantilever-based)
Low-Energy Electron Diffraction (LEED)
Reflection High Energy Diffraction (RHEED)
X-ray Photoelectron Spectroscopy (XPS)
Ultraviolet Photoelectron Spectroscopy (UPS)
Auger Electron Spectroscopy (AES)
Low-energy He+ ion scattering (LEIS)
Thermal Programmed Desorption Spectroscopy (TPD)

Of particular use for TACO is our combined Pulsed-Laser Deposition/Surface Science setup shown on the right-hand side. It allows the growth of multi-component metal oxides and the investigations of surface properties within the same UHV setup.