Catalysis by ultrathin
LaBO3 (B=Co, Fe) perovskite films
Perovskites are important catalysts, but detailed knowledge of their surface structure and chemistry is often lacking. The long-term objective of P08 is to elucidate structure-function correlations and visualize molecule-perovskite interaction in reactions involving O2, H2, CO, CO2, or H2O.
In the first project period, we will develop surface science-based model systems of LaCoO3 and LaFeO3 perovskites. Both epitaxial and polycrystalline thin films will be grown in UHV, guided by characterization via LEED, SXRD, SEM/EBSD, XPS/UPS/LEIS, IRAS, and TPD. Isotopically (18O or 13C) labeled adsorbates or films will reveal how oxygen and oxygen-containing molecules are activated. We will analyze the data in close collaboration with theoretical groups who simulate structure, stability, and infrared spectra (P03 Kresse).
We will employ a unique combination of in situ surface spectroscopy (PM-IRAS, NAP-XPS, SXRD) and in situ surface microscopy (PEEM, SPEM), combined with MS gas phase analysis, to monitor ongoing reactions from HV to atmospheric pressure. This procedure should enable us to gain fundamental insights into the interplay of ternary oxide atomic and electronic structure, defects, composition, adsorption, as well as initiation and spatial progression of surface reactions on the mesoscale via reaction fronts (local kinetics by imaging). Project P08 will create the required bridge between single crystals (P02 Diebold, P04 Parkinson) and more application-relevant nanomaterials (P10 Föttinger).
Our expertise is experimental surface science and its application to studies in heterogeneous catalysis. We operate a total of seven ultrahigh-vacuum (UHV) chambers, three of which are coupled to high-pressure cells. In situ and operando studies of surface reactions are carried out by area-averaging surface spectroscopy and real-time surface microscopy on the nano- and mesoscale. All chambers are equipped with facilities for sample preparation (sputtering, annealing, gas dosing), as well as various growth techniques (e-beam evaporators, Knudsen cells, sputter deposition). Analysis techniques used in our research include:
- Auger Electron Spectroscopy (AES)
- Field Emission Microscopy (FEM)
- Field Ion Microscopy (FIM)
- Gas Chromatography (GC)
- Low-Energy Electron Diffraction (LEED)
- Low-Energy Ion Scattering (LEIS)
- Mass Spectroscopy (MS)
- PhotoEmission Electron Microscopy (PEEM)
- Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRAS)
- Sum Frequency Generation (SFG)
- Scanning PhotoElectron Microscopy (SPEM)
- Scanning Tunneling Microscopy (STM)
- Temperature-Programmed Desorption (TPD)
- Ultraviolet Photoelectron Spectroscopy (UPS)
- X-ray Absorption Spectroscopy (XAS)
- Surface X-Ray Diffraction (SXRD)
- X-ray Photoelectron Spectroscopy (XPS)
- Prof. Andreas Stierle, DESY Hamburg, Germany: SXRD
- Dr. Luca Gregoratti, ELETTRA Sincrotrone Trieste, Italy: SPEM
The combined application of photoemission electron microscopy (PEEM) and scanning photoelectron microscopy (SPEM) is particularly beneficial for TACO because these techniques allow visualizing ongoing reactions and local surface analysis on a µm-scale.