  Percolation phenomena are investigated and discussed in three kinds of
nanostructures: first two are nanocrystalline silicon-based systems, Si
nanodots embedded in amorphous SiO2 matrix and porous silicon formed by an
oxidized nanowire network, and the third consisting of a multi-walled carbon
nanotube network embedded in amorphous SiN. The current-voltage characteristics
measured on first two systems present voltage percolation thresholds with the
same shape - a saturation plateau region of the current, followed by an abrupt
increase. The current-voltage and conductance-voltage curves measured on
multi-walled carbon nanotube network embedded in amorphous SiN present
non-periodic and temperature independent oscillations. These oscillations are
interpreted as voltage percolation thresholds.
