Ellipsometrische Untersuchungen zum Multilagenwachstum und zur Benetzung von Adsorbaten auf Graphit

• Applicant: Professor Dr. Klaus Knorr
• Subject Area: Condensed Matter Physics
• Term: from 1998 to 2003
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5105274

There have been already several examples of triple point wetting above and incomplete wetting below the bulk triple point. We want to search for a genuine wetting transition, one which does not coincide with a phase transition of the bulk system. For this purpose it is necessary to find an adsorbate or a technique which warrants a lower ratio of the adsorbate-substrate interaction and the adsorbate-adsorbate interaction. It is likely that this can be achieved by preplating the substrate with one or two monolayers of a less volatile adsorbate or by using molecules which interact not only by van-der-Waals but also by additional forces such as dipolar interactions or hydrogen bonding.Molecules of the latter type are aspherical with the consequence that their inclination with respect to the substrate is an additional degree of freedom of the adsorption process. In the first monolayer of some aspherical molecules there is indeed a phase transition from a structure in which the molecules lie flat on the substrate to one with a higher coverage in which they stand on the substrate. A prominent example is the planar molecule C2F3Cl which we have recently investigated by x-ray diffraction. Here the coverages of the flat and the perpendicular monolayer phase differ by a factor of two. The question arises of how this structural behavior is continued in the second and higher monolayers and whether it eventually affects wetting.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1052: Benetzung und Strukturbildung an Grenzflächen