AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS2+NS+BI+EL-TuM

Paper SS2+NS+BI+EL-TuM2
Characterization of the Alkanthiol/Metal Interface by High Resolution Core Level Spectroscopy

Tuesday, October 3, 2000, 8:40 am, Room 209

Session: Self-Assembled Monolayers
Presenter: K. Heister, University Heidelberg, Germany
Authors: K. Heister, University Heidelberg, Germany
H. Rong, University Heidelberg, Germany
M. Buck, University Heidelberg, Germany
L. Johansson, University Karlstad, Sweden
M. Zharnikov, University Heidelberg, Germany
M. Grunze, University Heidelberg, Germany
Correspondent: Click to Email
During the last decade X-ray Photoelectron Spectroscopy with a laboratory X-ray source became a conventional technique to characterize thiol derived SAMs. However, due to the mostly poor energy resolution, a strong attenuation of the photoelectron signal, and a low photoionization cross-section of the relevant core levels at high photon energies a precise binding energy analysis of an important building block of a SAM, the SAM/metal interface was hardly possible, even though high resolution photoelectron spectroscopy could give important information about the chemical state of the atoms in this region. Taking advantage of the high performance and tunebility of the third generation synchrotron sources we have firstly applied the synchrotron-based High Resolution Core Level Spectroscopy to study the SAM/metal interface. The variable photon energy of the synchrotron light and a high energy resolution of the spectrometer (0.1-0.3 eV) enabled us to resolve the bulk and surface components of the substrate emission peak (Au 4f / Ag 3d) and monitor the evolution of these components upon the alkanethiol and biphenylthiol adsorption. Simultaneously, the interaction of the thiol-derived molecules with the substrate was followed by monitoring the S2p doublet attributed to the sulfur head group of these molecules. Only one sulfur species was found in the densely packed SAMs, which implies an equivalent bonding geometry for all adsorbed molecules. In SAMs comprising of specially designed, mixed aliphatic-aromatic molecules a periodical, 'odd-even' shift of the S2p binding energy with the varying length of the aliphatic part was observed. This shift can be attributed to the distortion of the substrate-S bonding angle resulting from the unfavorable package conditions occurring at definite lengths of the aliphatic part. This work has been supported by the German Bundesministerium für Bildung, Wissenschaft und Technologie through grant No. 05 SL8VHA 2 and by DAAD.