Effect of ion implant dose on the mechanical properties of polyethersulfone films

Films of poly(ether sulfone) have been implanted with 50-keV As' in the dos e range of, 10(15) to 10(17) ions/cm(2). Nanoindentation tests were then co nducted on these films using a conical diamond tip with a 90 degrees includ ed angle, applying loads from 10 muN to 2 mN. The modulus and hardness were evaluated from the load-displacement data using the elastic unloading [J. Mater. Res. 7, 1564 (1992)] and the clastic-plastic unloading [J. Mater. Re s. 13, 421 (1998)] models. The latter approach gave more reliable values fo r the mechanical properties since it is not as sensitive to creep-in effect s. The implanted film showed as much as a twofold increase in hardness comp ared to the unimplanted polymer. However, the films with the highest dose d id not exhibit the maximum values or the mechanical properties. Hardness an d modulus values increased with increasing implantation dose up to 1 x 10(1 7) ions/cm(2) but dropped at higher doses, presumably due to a combination of sputtering of material and surface roughening. The dose dependence of th e mechanical properties is observed to have the same trend as are reported for the electrical properties.