  Highly conducting $SnO_{2}$ thin films were prepared by chemical spray
pyrolysis technique. One set of as-deposited films were annealed in air for 2 h
at 850$^{o}$C. These as-deposited and annealed films were irradiated using
$Au^{9+}$ ions with energy of 120 MeV at different fluences ranging from
$1\times10^{11}$ to $3\times10^{13}$ $ions/cm^{2}$. Electrical measurement
shows that as-deposited $SnO_{2}$ films are in conducting state with n = $3.164
\times 10^{20}$ $cm^{-3}$ and annealed $SnO_{2}$ films are in insulating state.
The amorphized latent tracks are created only above a certain threshold value
of $S_{e}$, which directly depends on the free electron concentration (n). The
electronic energy loss ($S_{e}$) of 120 MeV $Au^{9+}$ ions in $SnO_{2}$ is
greater than the threshold energy loss ($S_{eth}$) required for the latent
track formation in annealed $SnO_{2}$ thin film, but is less than $S_{eth}$
required for as-deposited $SnO_{2}$ film. Therefore, the latent tracks are
formed in the annealed $SnO_{2}$ film and not in the as-deposited $SnO_{2}$
film. Thermal spike model is used for the calculation of threshold energy loss
and radius of melted zone. The possible mechanism of the structural changes and
surface microstructure evolutions is briefly discussed in the light of ion's
energy relaxation processes and target's conductivity. The atomic force
microscopy (AFM) study of films shows that the morphologies of irradiated films
are linked with carrier concentration of target materials.
