NANOSCALE DEFORMATIONS OF POLYIMIDE WITH A FORCE MICROSCOPE

Grooves with nanometer scale dimensions can be fabricated on polymer s urfaces by moving the tip of an atomic force microscope (AFM) across t he surface at constant velocity and fixed applied force F. The grooves consist of a central trough with pile-ups on either side. These groov es are caused by plastic deformation and provide information about sur face mechanical properties. We describe new results on the Kapton poly imide. Groove shapes are measured from AFM images taken with zero appl ied force. The grooves are sufficiently shallow that image artifacts d ue to the tip shape are unimportant. The surface yield strength is fou nd to be about 125 MPa, as estimated from the applied force and the wi dth of the smallest groove, and is comparable to the bulk tensile stre ngth of 172 MPa. Grooves with pile-up heights that are large compared with the intrinsic surface roughness are found to have a universal sha pe when scaled to have the same heights and widths. Continuum mechanic s models developed for point indentations are not able to describe the properties of the grooves consistently.