Morphological differences between Bi, Ag and Sb nano-particles and how they affect the percolation of current through nano-particle networks

Abstract

Nano-particles of Bi, Ag and Sb have been produced in an inert gas aggregation source and deposited between lithographically defined electrical contacts on SiN. The morphology of these films have been examined by atomic force microscopy and scanning electron microscopy. The Bi nano-particles stick well to the SiN substrate and take on a flattened dome shape. The Ag nano-particles also stick well to the SiN surface; however they retain a more spherical shape. Whereas, many of the Sb nano-particles bounce off the SiN surface with only a small fraction of the Sb nano-particles aggregating at defects resulting in a non-random distribution of the clusters. These nano-scale differences in the film morphology influence the viability of applying percolation theory to in situ macroscopic measurements of the film conductivity, during the deposition process. For Bi and Ag nano-particles the increase in conductivity follows a power law. The power law exponent, t, was found to be 1.27 ±0.13 and 1.40 ±0.14, for Bi and Ag respectively, in agreement with theoretical predictions of t ≈1.3 for 2D random continuum percolation networks. Sb cluster networks do not follow this model and due to the majority of the Sb clusters bouncing off the surface. Differences in the current onset times and final conductance values of the films are also discussed.