AVS 47th International Symposium
    Surface Science Thursday Sessions
       Session SS2+NS-ThA

Paper SS2+NS-ThA9
Mechanical Behaviour of Confined Films: An In-situ Study of Silane Monolayers by Second Harmonic Generation (SHG)

Thursday, October 5, 2000, 4:40 pm, Room 209

Session: Tribology and Adhesion
Presenter: M.T. Strobel, University of Heidelberg, Germany
Authors: M.T. Strobel, University of Heidelberg, Germany
J. Blümmel, University of Heidelberg, Germany
W. Eck, University of Heidelberg, Germany
M. Buck, University of Heidelberg, Germany
M. Grunze, University of Heidelberg, Germany
Correspondent: Click to Email
Understanding the tribological properties of ultrathin organic films is of vital interest for their application in micro electro-mechanical systems (MEMS). To elucidate structural aspects of layers confined between two solids SHG was applied to trace force-induced changes of the polar and azimuthal orientation of molecular entities. As a model system monolayers of a silane bearing an SHG-active moiety were adsorbed on a glass-substrate. Mechanical loading and shearing of the film was achieved by a lens pressing against or rolling over the substrate. Mapping the contact area reveals pronounced, site dependent changes of both the tilt angle and the azimuthal alignment of the SHG active moiety upon loading. Whereas the azimuthal alignment persists after unloading and can be controlled by the rolling direction of the lens, the tilt angle is largely reversible for a loading unloading cycle. A quantitative evaluation of the data shows that the degree of the aligment is significantly larger than expected from simple models of contact mechanics.