Surface modification and nanoparticle formation by negative ion implantation of polymers

Negative ion implantation has been applied to fabricate metal nanocomposites of metals and polymers which are promising for nonlinear electronic, optical and biomedical applications. We have studied nanoparticle formation processes of Ag and their effects on surface properties of polymers, in comparison with those of Cu. Polycarbonate (PC) substrates were irradiated by negative Ag and Cu ions of 60 keV to various doses up to 3 × 1017 ions/cm2. Optical absorption spectra of the irradiated PC were measured in the range from 0.5 to 4.5 eV. Surface- and nanoparticle morphology of the PC were studied by AFM and cross-sectional TEM. Depth profiles of implant concentrations were evaluated by RBS. A surface-plasmon-resonance peak of Ag around 2 eV appears in the optical spectra of PC implanted to a dose of 1 × 1017 ions/cm2, whereas their defect absorption is not significant. The TEM and RBS measurements show that well-defined implantation is capable at this fairly low energy, though surface recession takes place because of ion sputtering. The structure of PC is stable enough for formation of Ag nanocomposites. Depth distribution of Ag nanoparticles significantly shifts towards the surface, differently from the case of Cu nanoparticles. Negative ion implantation provides nanoparticle formation for surface modification of polymers, with understanding the ion-induced precipitation processes in the polymers.