Dynamics and Manipulation of Adsorbate-Surface Interaction
The transfer of photoinduced hot electrons from the substrate into the adsorbate is a stimulative step in many photochemical processes at metal surfaces. The underlying mechanism is shown in the above schematic illustration. The photoexcited electrons of the substrate can tunnel through the surface barrier and become attached to the adsorbed molecules to form a temporary, negative molecular ion. After a period of time the electron is inelastically scattered back into an unoccupied electronic state of the metal substrate, leaving the adsorption system excited with some energy. One of the most important parameters for understanding this energy exchange is the resonance lifetime of the hot electron inside the adsorbate. This value is directly related to the amount of energy gained by the adsorbate. Time-resolved two photon photoemission (TR-2PPE) represents a powerful tool for investigating the electron dynamics in such an adsorbate/substrate system in the time domain.
We are interested in studying systematically the resonance lifetimes of different adsorbate/metal systems. An additional aim of our investigation is to determine how the density of electronic states should look for a metallic substrate which supports hot electron-induced surface reactions, e.g. the number of electrons available for a hot electron transfer is strongly reduced by relaxation processes and by the diffusion of the electrons away from the surface into the bulk. The dynamics of both competing processes can also be investigated by TR-2PPE technique.
In most recent work we we have studied the stability of a photoexcited adsorbate in interaction with a two-dimensional quantum well prepared by epitaxial growth of silver on a Cu(111) substrate. Our results show that the lifetime of an photoexcited cesium atom adsorbed at the quantum well is modified on a femtosecond time-scale as the well thickness varies between 1 an 30 ML.
Figure: lifetime of photoexcited Cesium adsorbed on a silver quantum well
- J. P. Gauyaqc. , A. G. Borisov, M. Bauer; accepted for publication in "Time-resolved Photoemission from Solids: Principles and Applications", Editors: M. Wolf und M. Aeschlimann, Springer Verlag.
- M. Bauer, M. Wessendorf, D. Hoffmann, C. Wiemann, A. Mönnich, M. Aeschlimann; Appl. Phys. A 80, (2005) 987.
- M. Wessendorf, C. Wiemann, M. Bauer, M. Aeschlimann, M. A. Schneider, H. Brune, K. Kern; Appl. Phys. A 78, (2004) 183.
- C. Lei, M. Bauer, K. Read, R. Tobey, T. Popmintchev, M. M. Murnane, H. C. Kapteyn; Phys. Rev. B 66, (2002) 245420; the paper has been selected for the January 2003 issue in the Virtual Journal of Ultrafast Science, http://www.vjultrafast.org.
- M. Bauer, C. Lei, K. Read, R. Tobey, J. Gland, M. M. Murnane, H. Kapteyn; Phys. Rev. Lett. 87, (2001) 025501; see also: "Shooting an X-ray movie", Phys. Rev. Focus, http://focus.aps.org/story/v8/st1, 7 July 2001
- M. Bauer, S. Pawlik, M. Aeschlimann; Phys. Rev. B 60 (1999) 5016.
- M. Bauer, S. Pawlik, M. Aeschlimann; Proc. of the 10th Annual Symposium of the Center for Photoinduced Charge Transfer, Rochester (1999).
- M. Bauer, S. Pawlik, R. Burgermeister, M. Aeschlimann; Surf. Sci., 402-404 (1998) 62.
- M. Bauer, S. Pawlik, M. Aeschlimann; Phys. Rev. B. 55 (1997) 10040.
- M. Bauer, S. Pawlik, M. Aeschlimann; Surf. Sci. 377-379 (1997) 350.
- M. Aeschlimann, M. Bauer, S. Pawlik; Chem. Phys., 205 (1996) 127.
- S. Pawlik, M. Bauer, M. Aeschlimann; in "Femtochemistry: Ultrafast Chemical and Physical Processes in Molecular Systems", Edited by: M. Chergui, World Scientific Publishing (1996).
- DFG priority program 1093 "Dynamics of electron transfer processes at interfaces"
- DFG-Graduiertenkolleg "Nichtlineare Optik und Ultrakurzzeitphysik"
- Forschungsschwerpunkt des Landes Rheinland-Pfalz "Optische Technologien und lasergesteuerte Prozesse (OTLAP)"