Microstructural effects on surface mechanical properties of ion-implanted polymers

Abstract

Tefzel, a copolymer of tetrafluoroethylene and ethylene, was implanted simultaneously with 400 keV boron, 700 keV nitrogen, and 600 keV carbon to a dose of 3 X 10¹⁵ ions/cm² for each ion. The implanted layer was examined using transmission electron microscope and compared with the pristine Tefzel for microstructural changes. The microhardness of the implanted and pristine Tefzel was determined using a nanoindentation technique. TEM bright-field images of the implanted layer show a patch-type contrast with distinguishable bright and dark regions. Electron energy loss spectroscopy (EELS) was used to show that the bright regions had a higher carbon concentration, as compared with the dark regions. The carbon-rich regions had an average size of approximately 40 nm. The pristine material showed a fairly featureless contrast with occasional local patchy regions. These were determined to be due to local thickness variations. The triple implantation improved the hardness of pristine Tefzel by over 66 times. The structure of the carbon-rich regions appears to be clusters of sp² bonded C atoms with sp³ sites present and hydrogen preferentially bonded in the sp³ C configuration. It was speculated that the carbon-rich regions could be harder than the surrounding regions, but this could not be resolved due to the small size of the regions.