Research


Molecular switching processes at surfaces

 

The aim of this project is to realize reversible conformational changes in adsorbed molecular switches via optical excitation in order to change and control the surface functionality. In addition to the direct (intramolecular) electronic excitation, the optically induced charge transfer between the substrate and the adsorbate plays a major role.  By means of time-resolved two-photon photoemission (2PPE) the electronic structure, the charge carrier dynamics and energetics of the molecular switches will be investigated.  For the detection of a conformational change we analyze modifications in the electronic structure und use vibrational spectroscopy in order to characterize the molecular orientaion by using sum-frequency generation (SFG)  and high-resolution electron energy loss spectroscopy (HREELS).  Furthermore we want to switch the non-linear optical response of the interface which will be probed with second harmanic generation (SHG).  Within this project both physisorbed  systems and molecular switches covalently attached to the substrate via anchoring groups will be studied.

 


 


Organic materials for applications in optoelectronic devices

The energetic position of molecular electronic states, i.e., occupied and unoccupied states, the charge carrier dynamics and energetics at interfaces between organic molecules (polymers) and metal or semiconducting surfaces will be determined by using time-resolved 2PPE and SHG. Furthermore the localization/delocalization (dispersion) of charge carriers are measured with angle-resolved 2PPE. The influence of these parameters on the efficiency of electronic and optoelectronic processes like in organic solar cell or light emitting diodes will be developed.

 


 

 

Interaction of pi-conjugated molecules with surfaces

 

Well-ordered and defect-free films with defined interfaces are needed to improve electronic devices based on organic molecules. The growth of such films is dominated by the adsorption structure of the first molecular layer, i.e. the molecules in direct contact with the substrate which is investigated in this project.  In particular, the adsorbate/substrate interaction between large pi-conjugated organic molecules adsorbed on metal surfaces and its influence on the binding energy, molecular orientation and local adsorption geometry are studied. For this purpose we utilize temperature programmed desorption (TPD) and  vibrational  spectroscopy (HREELS, SFG) as well as the near-incidence X-ray standing wave (NIXSW) technique.

 


 

Funding

  • Collaborative research center (Sfb 658): Elementary processes in molecular switches at surfaces"
    („Elementarprozesse in molekularen Schaltern an Oberflächen“)
 
 
  • Priority Program (SPP 1355): "Elementary processes in organic photovoltaics"
    ("Elementarprozesse der Organischen Photovoltaik")
 

 
  • "Nanoscale functional materials"