Alexander Föhlisch, PhD
University of Hamburg Faculty of Mathematics, Informatics and Natural Sciences Department of Physics Luruper Chaussee 149 22761 Hamburg Germany phone: +49-40-8998-3122 fax: +49-40-8998-2179

At the core of my research stands the investigation of the electronic structure and the ultrafast processes at surfaces, in molecules and solids in an atom specific way. To this end soft X-ray spectroscopic methods with synchrotron radiation sources and Free-Electron-Lasers (FEL) are used and developed further. Integral to my work are close collaborations with theoretical groups.

Attosecond and femtosecond charge transfer dynamics at surfaces.

The ultra fast charge transfer dynamic of atoms adsorbed on surfaces depends in fine detail on the orbital overlap and the substrate electronic structure. With core-hole-clock spectroscopy the charge transfer time of Sulfur on Ruthenium was determined to 320 attoseconds. Resonance stabilization on adsorbates due to the surface projected substrate band gap was determined experimentally and theoretically. The method is currently extended to investigate spin polarized charge transfer.

Surface chemical bonding from atom specific electronic structure determination.

To obtain an atom specific, chemical state selective and symmetry resolved description of the adsorbate valence electronic structure is investigated with resonant inelastic X-ray scattering, near edge X-ray absorption fine structure and high resolution photoelectron spectroscopy and. In combination with ab initio theory a significantly improved model of surface chemical bonding was achieved. Fundamental aspects of X-ray spectroscopic methods. The interpretation of resonant inelastic X-ray scattering as an atom specific and orbital symmetry selective electronic structure tool for adsorbates was given. Recently, the influence of ultra fast dynamics, vibronic coupling and Jahn–Teller distortions have been elucidated in collaboration with theory. Also an upper limit to interatomic coulomb decay in solids leading to a re-evalution of ‘multi atom resonant photoemission’. Electron correlation was investigated by resonant photoemission on transition metals Cu and Ni.

Towards novel X-ray spectroscopic tools with high brilliance, pulsed X-ray sources.

In the project “Multi-Photon and Non-Linear Processes as a Probe of Surfaces Dynamics” (Föhlisch,Wurth 3-year proposal) the goal is to develop novel X-ray spectroscopic tools, using the high brilliance and the short X-ray pulses of the Hamburg FEL in order to investigate dynamic processes in an element specific way. Also synchronized optical fs Lasers can be used. Here, concepts for novel experiments are being developed. For X-ray pump/probe experiments I develop a X-ray delay line based on a Mach-Zehnder interferometer with reflection/transmission gratings as beam splitter and mixer. We envisage to study electron correlation and dynamics and to establish novel spectroscopies like time resolved anti-Stokes X-ray Raman scattering.

First Experiments with the Hamburg vacuum ultraviolet Free Electron Laser.

Amongst the first experiments at the Hamburg VUV FEL we conducted in 2005 fundamental experiments on the photoionization cross section of noble gases, molecules and solids in high VUV radiation fields. In collaboration with M. Wolf we conducted a run on doubly resonant Sum Frequency Generation with Visible and VUV radiation to study magnetization dynamics and yield extreme interface sensitivity with elemental contrast.