Nonlinear conduction in platinum nanoparticle films

Platinum (deca)nanoparticles with a size between (25-150) nm have been deposited on a SiO₂/Si substrate by laser ablation. Roughly estimated, the particle distribution deviates from lognormal distribution at larger particle size. Electrical measurements on nanoparticle films with different surface coverage revealed that the films start conducting at a given percolation threshold. As expected, ohmic I-V characteristics were found in all investigated structures. However, below a voltage threshold, a transition from linear to pronounced nonlinear behaviour was observed in the samples with a higher surface coverage. A tunneling mechanism between the metal islands partially embedded into the substrate is proposed as a source of nonlinearity. This indicates an interaction between the nanoparticle film and the substrate, a conjecture strongly supported by the observation of some Pt₃Si lines in the X-ray diffractogram. Other possible causes of nonlinear conduction mechanisms are heuristically discussed.