RELATION BETWEEN SOLUTION CHEMISTRY AND MORPHOLOGY OF SNO2-BASED THIN-FILMS DEPOSITED BY A PYROSOL PROCESS

The chemical nature of precursors and morphology (surface aspect and preferred orientations) for SnO2 films deposited by a pyrosol process are examined for starting solutions containing either SnCl4 or SnCl2 . 2H(2)O dissolved in methanol. A study by comparison shows that molecules formed from SnCl4 deposit more easily than polymer molecules produced from SnCl2 . 2H(2)O. The addition of HCl in this last solution modifies significantly the chemical nature of the molecule participating in film development as well as the growth rate. Electrical measurements of the solution resistivity as a function of HCl concentration show a minimum in the equivalent conductivity which is directly correlated with a maximum in the growth rate, This is explained by the association of SnCl2 and HCl to form neutral HSnCl3 molecules. A geometrical approach is then developed to describe the growth form of the film crystallites. For thin films deposited from SnCl2 . 2H(2)O, the crystallite faces consist of {101} corresponding to (110) preferred orientation. For SnCl,, the crystallites consist of {111} faces corresponding to a (200) preferred orientation. The presence of (101) and (301) twin planes is used to explain the observation of (301) (211) and (101) preferred orientations respectively. Lastly, the electrical and optical characteristics of the corresponding films are also reported.