Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films

Abstract

We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films onSiO2 under nanosecond laser melting is dependent on film thickness. For films with thicknessh of2 nm ≤ h ≤ 9.5 nm, themorphology during the intermediate stages of dewetting consisted of bicontinuous structures. For filmswith 11.5 nm ≤ h ≤ 20 nm, the intermediate stages consisted of regularly sized holes. Measurement of thecharacteristic length scales for different stages of dewetting as a function of filmthickness showed a systematic increase, which is consistent with the spinodaldewetting instability over the entire thickness range investigated. This change inmorphology with thickness is consistent with observations made previously forpolymer films (Sharma and Khanna 1998 Phys. Rev. Lett. 81 3463–6; Seemann et al 2001 J. Phys.: Condens. Matter 13 4925–38). Based on the behavior of freeenergy curvature that incorporates intermolecular forces, we have estimated themorphological transition thickness for the intermolecular forces for Ag onSiO2. The theory predictions agree well with observations for Ag. These results show that it ispossible to form a variety of complex Ag nanomorphologies in a consistent manner, whichcould be useful in optical applications of Ag surfaces, such as in surface enhanced Ramansensing.