Electrical and optical property enhancement in multilayered sol-gel-deposited SnO2 films

When prepared by the sol-gel dip-coating technique, doped tin oxide films need several superimposed layers to reach the expected low sheet resistance. In this paper we show that successive depositions increase the uniformity and homogeneity of multi-layered sol-gel tin oxide alms. The final thickness is always found to be lower than a multiple of the initial first layer thickness, indicating that densification occurs. A strong improvement of physical properties is jointly observed in this multilayered configuration. All parameters (atomic density, refractive index, electrical resistivity, optical transmission and reflectivity) evolve towards bulk material values. This is explained by the fact that the sol, in which is dipped the substrate, fills in the pores or cracks remaining in the previously deposited layers. The quality of the sol-gel tin oxide stacked deposits obtained in such a way is evidenced by the M-line spectroscopy experiments presented in this paper. It is shown that multilayered coatings are able to guide light over some millimetres.