Electrical conductivity and Young's modulus of flexible nanocomposites made by metal ion implantation of Polydimethylsiloxane: the relationship between nanostructure and macroscopic properties

The mechanical and electrical properties of nanocomposites created by gold and titanium implantation into Polydimethysiloxane (PDMS) are reported for doses from 1015 at/cm2 to 5x1016 at/cm2, and for ion energies of 2.5 keV, 5 keV and 10 keV. TEM cross-section micrographs allowed detailed microstructural analysis of the implanted layers. Gold ions penetrate up to 30 nm and form crystalline nanoparticles whose size increases with ion dose and energy. Titanium forms a nearly homogeneous amorphous composite with the PDMS up to 18 nm thick. Using TEM micrographs, the metal volume fraction of the composite was accurately determined, allowing both electrical conductivity and the Young’s modulus to be plotted vs. the volume fraction, enabling quantitative use of percolation theory for nanocomposites less than 30 nm in thickness. This allows linking the composite’s Young’s modulus and conductivity directly to the implantation parameters and volume fraction. Electrical and mechanical properties were measured on the same nanocomposite samples, and different percolation thresholds and exponents were found, showing that while percolation explains very well both conduction and stiffness of the composite, the interaction between metal nanoparticles occurs differently for determining mechanical and electrical properties.