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Theoretical surface science

We are interested in both stationary and, even more so, in dynamical aspects of adsorbates at solid surfaces. These play a role in such diverse fields as heterogeneous catalysis, surface lithography, photocatalysis, and electrochemistry. For dynamics, adiabatic and non-adiabatic processes are studied. In the first case, the adsorbate remains in the electronic ground state while in the latter electronic excitations are involved. The most prominent examples of non-adiabatic events are photo- and STM- (Scanning Tunneling Microscope) induced reactions. Both are interesting for applications (microstructuring of materials, surface photo- and femtochemistry, photocontrol, single molecule manipulation), and for fundamental reasons (treatment of ‘open’, driven quantum systems in contact with a ‘bath’ of surrounding modes). Using quantum dynamical (open-system density matrix theory, wave packet propagation) and quantum chemical methods, the following topics / reactions are investigated (for reviews, see [42,73,76] – numbering refers to publication list):

  • Photodesorption of atoms and small molecules from metal surfaces[12,15,20,21,22,24,25,29,30,35,42,43,45,46,47,54,59,63,65,71,73,74,78,79,88,90,100,116,119,134].
  • Photoswitching of molecules at surfaces[101,107,111,120,124,126,141,142].
  • STM-induced desorption and reactions (e.g., switching) of atoms and molecules at semiconductor and metal surfaces[36,40,47,53,60,75,80,89,93].
  • Electron-stimulated desorption of small molecules from metal surfaces[55,56].
  • (Femtosecond) Laser control of surface chemical reactions (UV/vis, IR)[16,17,27,37,38,45,71,76,78,88,90,92,100,125,131,132].
  • Quantum chemistry of photo- /STM-active adsorbates[34,40,75,80,88,90,93,100,101,106,127].

Examples of adiabatic processes are elastic, inelastic, and reactive scattering of atoms and molecules from rigid and nonrigid surfaces and the energy transfer of vibrationally excited adsorbates to the surface. We develop, test and apply, various time- independent and time-dependent quantum methods to treat scattering/energy transfer of atoms and molecules at/to metal and semiconductor surfaces. Specific examples are:

  • Time-independent reactive scattering and rate theory for the dissociative sticking of diatomic molecules at rigid metal surfaces[10,11].
  • Development and application of wavepacket methods for the scattering of atoms and molecules at rigid and nonrigid metal surfaces[23,31,33,41,44,45].
  • Development and application of open-system density matrix based methods for gas-surface scattering[26,35,48,52,96].
  • Vibrational relaxation of adsorbates by vibration-phonon or vibration-electron hole pair coupling[53,60,72,73,76,77,78,81,83,93,103,110,115,125,131,132].
  • IR-laser pulse induced vibrational excitation and reactions of adsorbates[27,37,38,74,83,88,90,92,94,100,03,110,115,125,131,132].

 

 

Animation of STM-induced desorption

The video shows an artistic rendering of the STM induced desorption of chlorobenzene from a Si(111) 7x7. The different types Si-atoms -- rest-, ad-, dimer-, corner hole- , top layer- and "bulk"-atoms -- are represented by different shades. The STM tip approaches the surface from above and injects a charge carrier (electron or hole) represented by the colored light source. The charge carrier loses energy after injection (color change) and then diffuses at the surface. Finally one chlorobenze is transferred into the physisorbed state (flat molecule) and desorbs (see e.g. Phys Rev Materials 1 026001 (2017) and references therein).