Surface modification of polytetrafluoroethylene by Ar+ irradiation for improved adhesion to other materials

Abstract

A surface of thin square polytetrafluoroethylene (PTFE) samples (1 x 1 x 0.2 cm(3)) was irradiated with Ar+ at 1 keV with varying ion dose from 5 x 10(14) to 1 x 10(17) ions/cm(2) with and without an oxygen environment. The irradiated surface of the samples was examined by scanning electron microscopy (SEM) for surface textural changes and x-ray photoelectron spectrometry (XPS) for changes in chemical structure. A wettability test was conducted on the irradiated surface of PTFE samples by water droplets. A Scotch(TM) tape adhesion test, after a thin film of Cu or Al was evaporated on the irradiated surface, and a tensile test after irradiated samples were glued to sample holders by an adhesive glue (Crystal Bond) was also run. The SEM micrographs showed increasing roughness with fiber forest-like texture with increasing ion dose. The Ar+ with an O-2 environment produced finer and denser fiber forest-like texture than that without O-2. The high-resolution XPS spectra showed decreased intensity of the F1s peak and formation of the Ols peak when irradiated with the O-2 environment. The increase of the O1s peak. may be attributed to the reaction of oxygen atoms and the free radicals created by Ar+ bombardment. The wettability of water droplets on the irradiated surfaces was found to be inversely proportional to the surface roughness. Adhesion tests were conducted on 2000 Angstrom thick Al or Cu film. Full detachment of the metal films was observed when PTFE samples were not modified. Partial detachment of the Al film occurred when PTFE was irradiated without the O-2 environment, regardless of ion dose. No detachment of the film occurred when PTFE was irradiated with the O-2 environment with the ion dose exceeding 1 x 10(16) ions/cm(2). Partial detachment of Cu film was observed with or without the O-2 environment when the ion dose was 5 x 10(14) ions/cm(2). No detachment occurred with or without the O-2 environment when the ion dose was 1 x 10(15) ions/cm(2) or greater. The tensile test showed that adhesion of an adhesive cement (Crystal Bond) to the irradiated PTFE samples increased significantly with increasing ion dose up to 1 x 10(16) ions/cm(2). Possible mechanisms for the improved adhesion are given. (C) 1997 John Wiley & Sons, Inc.