AVS 50th International Symposium
    Applied Surface Science Tuesday Sessions
       Session AS-TuM

Paper AS-TuM5
Solvent Enhanced Surface Modification of Polymers Accompanying AFM Tip Induced Mechanical Stresses

Tuesday, November 4, 2003, 9:40 am, Room 324/325

Session: Image Analysis and Polymer Characterization
Presenter: F. Stevens, 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 an AFM tip in contact mode in a solvent, material is not worn away, but rather the polymer surface expands forming a nanometer scale "protrusion" at and surrounding the scanned location. Furthermore, for sub-micron scan areas one observes 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 made 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 of several molecular weights in four solvents with dramatic differences in response. We present evidence that both plastic deformation and tip induced swelling play major roles in the observed polymer surface modification by AFM. Extending this work, we have added temperature as a parameter, performing the tip stimulation at temperatures from 0 - 120 C. Major changes in the structures formed occur at higher temperatures due to increased solvent mobility and polymer mechanical properties with temperature.