Percolation transition in the gas-induced conductance of nanograin metal oxide films with defects

We use Monte-Carlo Simulations to study the conductance switching generated by gas-induced electron trapping/-releasing in films of sintered metal oxide nanoparticles by using a site-bond percolation model. We explore the possibilities of gas sensors based on these mechanisms. In our study, we model films of different thicknesses where the conductance values of the grains (sites) and of the contacts (bonds) between these grains depend on the surface density Nr of adsorbed gas molecules from the ambient atmosphere. Below a critical density Nr=Nr,c, the system is insulating due to the interruption of current flow, either through the connecting bonds or through the grain interior. This leads to two competing critical gas covering thresholds Nr,c(bond) and Nr,c(site), respectively, that separate the insulating from the conducting phase. For Nr,c(site)>Nr,c(bond), the characteristic curve of monodisperse sensors shows a noticeable jump from zero to a finite conductance at Nr=Nr,c(site), while for polydisperse ...