Metal/polymer interfaces with designed morphologies

Abstract

The morphology of a metal/polymer interface is important for many properties, e.g. its adhesional strength. Starting from the basic processes occurring in the initial stages of metal/polymer interface formation, it is possible to obtain different morphologies by variation of the preparation conditions. In this report we present selected examples from our own work of how metal/polymer interfaces with different morphologies can be prepared by evaporating noble metals (Au, Ag, Cu) onto chemically different polymers, i.e. bisphenol-trimethyl cyclohexane polycarbonate (TMC-PC), pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide (PI), and on Teflon AF 1601. The interfaces were characterized using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The combination of these techniques allows one to determine morphological parameters such as the concentration and distribution of metal clusters at the surface and in the near-surface region. Using low deposition rates and elevated temperatures, spread-out metal/polymer interfaces can be formed, whereas the use of high deposition rates and moderate temperatures results in relatively sharp interfaces. Another approach to obtain a defined morphology is to form large metal clusters of 10-30 nm diameter on the polymer surface and embed them into the polymer in a controlled manner by a subsequent annealing process. First experiments on the macroscopic adhesion of Au and Cu on TMC-PC showed that the initially low peel strength could be increased substantially by subsequent annealing above the glass transition temperature.