Project Details
Projekt
Molecular Orbital Tomography: Organic Interfaces and Surface Reaktions
Subject Area
Experimental Condensed Matter Physics
Term
from 2014 to 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 240624954
The properties of molecules are crucially influenced by the highest occupied and lowest unoccupied molecular orbitals. Imaging of the spatial distribution of these orbitals is thus scientifically highly interesting. Recently angle resolved photoelectron spectroscopy (ARPES) has been established to experimentally access this spatial orbital information. Against other techniques like higher harmonics generation, electron-momentum spectroscopy or scanning tunneling microscopy this molecular orbital tomography by ARPES has essential advantages such as, e.g., a faster data acquisition. The theoretical description of ARPES is generally complicated. However, using a plane-wave approximation for the final state it can be brought into a simple form, which renders the angle dependent ARPES intensity distribution as a Fourier transform of the respective molecular orbital. This approach allows rather directly connecting the molecular orbital with the ARPES measurement and thus interpreting the experimental data. Within the project SCHO 1260/4-1, funded by the DFG since 2014, we have been able to work very successfully in the last 2½ years and parts of the achieved results have been published already in six publications. These results and the particular timeliness of the topic provide several links for this continuation proposal, in which the following investigations are intended:(i) Methodological Aspects: Limitations for the Application of the Plane-Wave-Approximation:The limitations of -orbital tomography are immediately connected to the approximation of the final state by a plane wave. There are indications for deviations from this plane wave final state at certain energies of the outgoing electrons. In this subproject photon energy- and angle-dependent data will be recorded over a large momentum and energy region to distinguish and quantify possible contributions from forward scattering, back scattering, or diffraction on neighboring atoms. The applicability of orbital tomography to non-planar systems will furthermore be tested on the model system C60. Due to the spherical symmetry of this molecule a pronounced influence of scattering effects is expected in this case.(ii) Application of Orbital Tomography to Particular Systems:Imaging of orbitals with high energy resolution: In case of excitation of vibrations the motion of the molecular backbone leads to a change of the geometric distribution of the electronic wave function. To image these distorted orbitals in real space and reconstruction of the phase, experiments on weakly coupled, low-symmetric molecules are planned.Hybridization at molecule-molecule-interfaces and its influence on orbitals: By means of orbital tomography possible new hybrid states at molecule-molecule-contacts will be investigated, which will crucially contribute to the understanding of doping in organic semiconductor materials.
DFG Programme
Research Grants
