MODIFICATION BY PLASMA EXPOSURE OF PHYSICAL CHARACTERISTICS OF THIN FILMS OBTAINED FROM TIN TETRACHLORIDE SOLUTION
Keywords:
thin films of tin dioxide, sol-gel method, plasma exposure, tin tetrachlorideAbstract
In this paper, the change in the physical characteristics of thin films obtained from a solution of tin tetrachloride after treatment with hydrogen and oxygen plasmas, is studied. Processing by hydrogen plasma of a glow discharge leads to a decrease in the transparency of the film by 3-15%, while treatment with oxygen plasma leads to only a slight (1-5%) decrease of the transparency. A noticeable decrease in the transparency of the film after treatment with hydrogen plasma is explained by the formation of opaque SnO compounds, which increase the absorption coefficient from 2.5·103 to 5.91·103 cm-1 and which affect the electrical characteristics of the film.Processing in oxygen plasma does not involve the formation of SnO, and a slight change in the transparency of the film is associated with the destructive effect of plasma on the structure of SnO2 crystallites.
Treatment in an oxygen plasma leads to a decrease in the size of SnO2 crystallites. It is assumed that this is due to the destructive action of massive oxygen ions of the plasma on the structure of the crystallites. The observed increase in the film density with a proportional decrease in its thickness is explained by the filling of intercrystalline voids with SnO2 clusters. It has been established that the treatment in hydrogen plasma of tin dioxide films synthesized by the sol-gel method leads to an increase in the size of SnO2 crystallites. It is suggested that the increase is caused by the segregating action of light hydrogen ions in the plasma, which leads to the rearrangement and integration of crystallites as it occurs in isothermal annealing. Reduction of the film thickness by 10% while maintaining the film density is explained by the formation and desorption of H2O molecules. This leads to the appearance of a large number of oxygen vacancies, the formation of SnO molecules on the surface of the SnO2 crystallites, and, as a consequence, to a decrease in the stoichiometry and transparence of the film.It was obtained that, after processing in plasma, the absolute values of the resistance of the SnO2 film synthesized by the sol-gel method and the slope of the temperature dependence curve depend significantly on the type of plasma-forming gas. It is assumed that the type of plasma- forming gas (H2 or O2) affects the concentration of oxygen vacancies in the film.
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