AVS 45th International Symposium
    Nanometer-scale Science and Technology Division Monday Sessions
       Session NS+SS-MoM

Paper NS+SS-MoM11
In-situ Investigation of the Influence of a Mechanical Load on the Orientation of Organic Monolayers with Second Harmonic Generation

Monday, November 2, 1998, 11:40 am, Room 321/322/323

Session: Tribology, Adhesion and Interfacial Forces
Presenter: F. Eisert, University of Heidelberg, Germany
Authors: M. Gurka, University of Heidelberg, Germany
F. Eisert, University of Heidelberg, Germany
M. Buck, University of Heidelberg, Germany
M. Grunze, University of Heidelberg, Germany
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Understanding mechanical properties of ultrathin organic films is of fundamental importance due to their vital role in numerous technological applications such as hard disc drive lubrication or as moulde release agents in the injection moulding process. The relationship between macroscopically applied forces and processes taking place on the molecular scale can be studied in situ by photon-based techniques. Second harmonic generation (SHG) is a nonlinear optical technique which allows to investigate the effect of normal and shear forces on the order and orientation of confined monolayers. We have set up a model experiment consisting of an SHG-active silane film self-assembled onto a glas prism. A pressure in the range of 30 - 50 MPa is applied to the monolayer by pressing a quartz lens against the prism. Changes of the film structure are monitored by in situ polarization dependent SHG experiments. The SHG signal reflects the response of the SHG-active endgroup of the monolayer to the mechanical load and allows to determine the average tilt angle of the monolayer and also the in-plane symmetry of the molecular layer. During loading we observe only a minor change in the mean tilt angle of the endgroup whereas shear forces cause the molecules to align.