IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Applied Surface Analysis Tuesday Sessions
       Session AS-TuM

Paper AS-TuM8
Solvent-Assisted Modification of Polymer Surfaces Using Scanning Force Microscopy

Tuesday, October 30, 2001, 10:40 am, Room 134

Session: High Spatial Resolution and Imaging
Presenter: R. Leach, Washington State University
Authors: F. Stevens, Washington State University
R. Leach, Washington State University
J.T. Dickinson, Washington State University
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The response of thin polymer films and bulk surfaces to combined stress and solvent is important for applications such as protective barriers (e.g., various wrappings), in controlled drug release from polymer hemispheres, resists for lithography, and nanometer scale surface modification. Over a wide range of normal forces, when a polymer is scanned by SFM in contact mode in a solvent, material is not worn away, but rather the polymer surface expands forming a nanometer scale "bump" at and surrounding the scanned location. Furthermore, for sub-micron scan areas one often observs a series of parallel ridges (moguls) perpendicular to the fast scan direction. Previous reports of the formation of raised material have nearly all been in air, required long times or very high forces to form; little evidence has been presented for the mechanism of formation. We have engaged in a detailed study of protrusion formation and raised ridges using poly(methyl methacrylate) in alcohol based solvents. In addition to scanning in air, we have scanned the polymer surface in four solvents with dramatic differences in response. We have also observed the effects of varying contact force, and the effect of using cantilevers with different force constants. We present evidence that both plastic deformation and tip induced swelling play major roles in the observed polymer surface modification by SFM. The stresses applied by the tip generate tensile forces around the tip that likely increase the quantity of solvent that can enter the surface. We show that adding Rhodamine 6G dye to the solvent provides us with evidence that indeed solvent is going into the polymer. Using fluorescence microscopy we can monitor the uptake of dye as a function of scanning and solvent parameters. This study also shows the possibility of introducing small quantities of a chemical into the polymer surface in a highly localized (nanometer scale) fashion.