AVS 46th International Symposium
    Surface Science Division Friday Sessions
       Session SS1+AS+BI-FrM

Paper SS1+AS+BI-FrM7
Multilayer Phases in Self-Assembled Monolayers Based on Silane Coupling Agents

Friday, October 29, 1999, 10:20 am, Room 606

Session: Organic Films/Self-Assembled Monolayers
Presenter: B.C. Bunker, Sandia National Laboratories
Authors: B.C. Bunker, Sandia National Laboratories
R.W. Carpick, Sandia National Laboratories
M. Hankins, Sandia National Laboratories
M.L. Thomas, Sandia National Laboratories
R. Assink, Sandia National Laboratories
M. DeBoer, Sandia National Laboratories
Correspondent: Click to Email
Thin films prepared using silane coupling agents are used extensively to chemically modify surfaces. In micromachines, such films are used to control stiction, friction, and adhesion of moving parts. The films are commonly depicted as self-assembled monolayers, in which each silane molecule forms extensive Si-O-Si linkages to the surface and to other molecules. However, many workers report that it is difficult to produce self-assembled monolayers on a reproducible basis, especially for films having fluorinated hydrocarbon chains. In this paper, atomic force microscopy studies are used to show that irreproducible film formation is associated with the fact that silane coupling agents can self-assemble into a range of structures described in common surfactant phase diagrams. Evidence is presented suggesting that hydrocarbon and fluorocarbon silanes form lamellar and inverse micelle structures on silica and silicon nitride surfaces. In some instances, multilayer structures are produced during fabrication. Films which start out as monolayers can also reorganize into multilayer phases after deposition. Factors influencing the phases observed include surface pretreatment, the solvent, silane and water concentrations in the deposition solution, and environmental parameters such as temperature and relative humidity. Mechanisms for the evolution of the observed range of self-assembled structures vs. reaction conditions are described.