Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films

TL;DR

This study investigates how the thickness of ultrathin silver films influences their spontaneous dewetting patterns during nanosecond laser melting, revealing a systematic transition from bicontinuous structures to hole formations.

Contribution

It demonstrates the thickness-dependent morphological pathways of Ag film dewetting and provides a theoretical estimate for the transition thickness based on intermolecular forces.

Findings

Dewetting morphology depends on film thickness.

Spinodal dewetting instability observed across thickness range.

Theoretical predictions match experimental observations.

Abstract

We show here that the morphological pathway of spontaneous dewetting of ultrathin Ag films on SiO2 under nanosecond laser melting is found to be film thickness dependent. For films with thickness h between 2 <= h <= 9.5 nm, the morphology during the intermediate stages of dewetting consisted of bicontinuous structures. For films 11.5 <= h <= 20 nm, the intermediate stages consisted of regularly-sized holes. Measurement of the characteristic length scales for different stages of dewetting as a function of film thickness showed a systematic increase, which is consistent with the spinodal dewetting instability over the entire thickness range investigated. This change in morphology with thickness is consistent with observations made previously for polymer films [A. Sharma et al, Phys. Rev. Lett., v81, pp3463 (1998); R. Seemann et al, J. Phys. Cond. Matt., v13, pp4925, (2001)]. Based on the behavior of free energy curvature that incorporates intermolecular forces, we have estimated the morphological transition thickness for the intermolecular forces for Ag on SiO2 . The theory predictions agree well with observations for Ag. These results show that it is possible to form a variety of complex Ag nanomorphologies in a consistent manner, which could be useful in optical applications of Ag surfaces, such as in surface enhanced Raman sensing.