Strain sensitivity in ion-implanted polymers
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Strain sensitivity in ion-implanted polymers Giovanni Di Girolamo1, Marcello Massaro1, Emanuela Piscopiello1, Emanuela Pesce1 Ciro Esposito1, Leander Tapfer1 and Marco Vittori Antisari2 1
ENEA, Dept. Adv. Phys. Technol. and New Materials (FIM), Brindisi Research Center, Strada Statale “Appia” km 713, 72100 Brindisi, Italy 2 ENEA, Dept. Adv. Phys. Technol. and New Materials (FIM), Casaccia Research Center, Via Anguillarese 301, 00123 Rome, Italy ABSTRACT Ion implantation process was used to fabricate ultra-thin conducting films in inert polymers and to tailor the surface electrical properties for strain gauge applications. To this aim, polycarbonate substrates were irradiated at room temperature with low energy Cu+ ions of 60 keV at 1 µA/cm2 and with doses ranging from 1x1016 to 1x1017 ions/cm2. XRD and TEM measurements on the nanocomposite surfaces demonstrated the spontaneous precipitation of Cu nanocrystals at 1x1016 ions/cm2 fluence. These nanocrystals were located at about 50 nm - 80 nm below the polymer surface in accordance with TRIM calculations. Optical absorption spectra exhibited a surface plasmon resonance (SPR) at 2 eV, in accordance with the formation of Cu nanoparticles. For doses of 5x1016 ions/cm2 the formation of a continuous nanocrystalline Cu subsurface film occurred and a well pronounced SPR peak was observed. Otherwise, for higher doses (1x1017 ions/cm2) a damaged and structurally disordered film was obtained and the SPR peak was smeared out. Electrical conductivity measurements clearly indicated a reduced electrical resistance for the samples implanted with a doses up to 5x1016 ions/cm2, whereas higher doses (1x1017 ions/cm2) resulted detrimental for the electrical properties, probably due to the radiation induced damage. The dependence of electrical resistance from surface load was evaluated during compression tests up to 3 MPa. A significant linear variation of the electrical resistance with the surface load was found and could be related to the changes in the spatial distribution of nanoparticles inside the copper film.
INTRODUCTION Polymer-based composites are very attractive materials for the realization of high response pressure, strain and mechanical devices. These transducers are particularly suitable for in-service monitoring and diagnostics of the structural stability and mechanical strain of components in aeronautics, aerospace and automotive. At this purpose, metallic ion implantation is a promising technology to modify the surface properties of insulating polymers [1]. Previous works have demonstrated that low energy Cu- ion implantation in polymers may provide the precipitation of metal nanoparticles below their surface [2,3,4]. It has been also reported that low energy Co+ ion irradiation of viscous polymers may be optimized for synthesis of a metallic dispersion or a quasi-continuous film into the polymer surface layer [5]. Since both high energy and current density produce significant thermal effects on the exposed polymer surface, the final structure would resu
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