Morphology of ultrathin gold and copper coatings thermally evaporated on polydimethylsiloxane elastomers: From isolated nanoparticles to continuous coatings

Abstract

This article presents a morphological study of ultrathin gold and copper coatings (between 1 nm and 20 nm equivalent metal thickness) thermally evaporated on polydimethylsiloxane (PDMS). Results are discussed on the basis of transmission electron microscopy and atomic force microscopy. Gold is demonstrated to grow in the form of isolated particles following a Volmer-Weber growth mode, whereas copper more likely grows in the form of a continuous film, following a Stranski–Krastanov growth mode. Our results demonstrate a negligible role of the PDMS elastic modulus (between 0.5 and 2.5 MPa) in the gold and copper coatings morphology respectively. However, significant morphological changes are observed when the metals are thermally evaporated on a PDMS substrate of extremely higher surface elastic modulus obtained after O2 plasma exposure.