Leveling and dewetting processes of nanoindentation-induced defects on thin polymer films

We study the effect of nanoindentation-induced indents on polystyrene (PS) films (thickness = h > 100 nm), spin-cast on silicon substrates. Indents with residual depths of penetration, z_D, comparable to the film thicknesses leveled (healed) upon heating above the glass transition temperature (T_g) of bulk PS, resulting in a flat polymer surface. Deep indents which clearly penetrated the films and damaged the substrate dewetted from the silicon surface. The healing rate, dz_D/dt, was measured for several molecular weight PS films and found to scale with the curvature of the hole bottom, H_D, as (dz_D/dt) H_D^0.52±0.05. Measurements were performed using atomic force microscopy. The healing rate was found to be, in general, higher than the dewetting rate of the laterally expanded deep indents.