A criterion for dewetting initiation from surface disturbances on ultrathin polymer films

Nanoindentation-induced defects on ultrathin (h = 17 nm) polystyrene (PS) films that are spin cast on silicon (Si) substrates, with residual depths of penetration lower than the film thickness (<17 nm), can either grow to initiate dewetting or level, which results in a flat polymer surface, upon heating above the glass-transition temperature (T _g). The excess surface energy (ΔF _γ) of the system, which is added to the initially flat coating with the formation of an indent, provides a critical value, ΔF _γ,crit = 6.1 × 10 ^-16 J, which determines indent evolution upon annealing. An indent grows when ΔF _γ > ΔF _γ,crit and levels when ΔF _γ < ΔF _γ,crit. This conclusion is in agreement with previous reports, which used ΔF _γ to distinguish the two (dewetting/leveling) opposing processes (1) in the case of indents deeper than the film thickness and (2) in the case of built-in ordered surface disturbances by capillary force lithography.