Ion beam induced enhanced adhesion of Au films deposited on polytetrafluoroethylene

Abstract

Considerable efforts have been made to improve the physical and chemical properties of a large number of polymers by ion implantation, and the enhancement of various properties was attributed to different mechanisms like chain scission, cross-linking and carbonization. It was observed that ion implantation can also improve the surface properties of polytetrafluoroethylene (PTFE) but the mechanisms for such enhancement are not completely clear yet. In this work we have studied the adhesion of Au thin films on PTFE. The PTFE substrates were implanted with 160 keV N ions to a dose range between 1×10 14 and 1×10 17 ions/cm 2. The treated samples were examined by visible (514.5 nm) and FT infrared (1064 nm) Raman spectroscopy as well as by scanning electron microscopy. Ion implantation on PTFE in the low dose range leads to the splitting of weaker CC bonds; in the intermediate dose range sputter loss effects are dominant, and at higher doses, the microstructure strongly evolves and double CC bonds are created. Before and/or after the ion pretreatment, the specimens were coated (with a sputtering technique) with 150 nm thick Au films. Adhesion properties of the films were assessed by conventional scratch- and scotch-tape tests in conjunction with optical microscopy. In the case of pre-deposited coatings, enhanced adhesion occurs only if the implanted dose is lower than 2×10 14 ions/cm 2, in connection with the formation of dangling bonds in the polymer (‘chemical’ adhesion), as confirmed by contact angle measurements. In the case of post-deposited coatings, enhanced adhesion occurs in the whole dose range. In the medium-high dose range, the enhanced adhesion can be related to the development of surface topography of the polymer substrate (‘mechanical’ adhesion).