CONTACT AFM ON SOFT SURFACES - ELASTICITY AND FRICTION EFFECTS

We present contact AFM images of an annealed film of latex balls of 5 degrees glass transition temperature. Surface appears to be constituted of an hexagonal arrangement of flatten spheres. Contrast is seen to depend very much on the applied load and on the scan direction: spheres appear concave or convex according to these parameters. An analysis of the friction clearly shows that there are two regimes for imaging. For high magnifications, the tip is deeply intruded in the material and images do not reflect the topography of the surface but seem to be characteristic of its mechanical properties. For higher scan domains, friction is of classical type and resolution is good. These results permit to clarify the limitations of the technique applied on soft materials.