Treatment of polymers by plasma immersion ion implantation for space applications

Kapton samples were implanted with aluminum in order to create a metal oxide layer for protection against atomic oxygen degradation in space environment. Three different approaches were used. First, an aluminum plasma was created by vacuum arc discharge in a magnetic field, and samples were implanted by plasma immersion. Although sample charging problems prevented implantation at significant depths, an ion mixing layer was formed, as shown by X-ray Photoelectron Spectroscopy (XPS) depth profile analysis, giving superior adhesion of the aluminum film to the substrate. In a second approach, a 20-nm aluminum film was deposited on a Kapton sample by electron beam, followed by nitrogen plasma immersion ion implantation. Rutherford Backscattering Spectroscopy (RBS) analysis did not show significant recoil implantation of aluminum, and the process resulted in a cracked film, possibly due to the formation of a stressed aluminum nitride layer. In a third approach, direct aluminum implantation by plasma immersion was made without a confining magnetic field. Charging problems are minimized in this low-density plasma, but an increase of a factor of 10 in treatment time was not enough to compensate the much lower dose implanted per pulse. This was revealed by oxygen degradation tests made by submitting the treated samples to RE oxygen plasmas and measuring the mass loss. The sample implanted in magnetically confined plasmas conserved its transparency and had negligible mass loss. Unconfined plasmas also resulted in a degradation protection layer but only in small patches of the substrate since the low dose and possibly a misalignment resulted in poor uniformity. Thermal transients followed by adhesion tests showed that direct implantation gives the necessary adhesion of the protective layer in order to withstand the harsh space environment.