Reducing gas-sensing performance of Ce-doped SnO2 thin films through a cosputtering method

SnO2 thin films doped with various concentrations of Ce were grown by cosputtering Sn and Ce metallic targets in an Ar/O-2 mixed atmosphere. The cerium concentrations in the SnO2 films were varied from 1.2 to 4.5 at% by varying the Ce sputtering power during thin-film growth. Surface morphology analysis revealed that the surface roughness of the Ce-doped SnO2 thin films increased with an increase in cerium concentration. X-ray diffraction and transmission electron microscopy analysis results indicated that the Ce-doped SnO2 thin films were highly crystalline. Furthermore, Ce ions in the SnO2 thin films had mixed valence states; moreover, the oxygen vacancy density increased with an increase in Ce concentration. An increased Ce concentration in the SnO2 thin films engendered the roughening of the Ce-doped SnO2 film surface and increased the concentration of Ce4+ ions and oxygen vacancy number near the film surface. These factors are advantageous for enabling the adsorption of a relatively large number of oxygen ions on the film surface; therefore, increased ethanol vapor sensing responses of Ce-doped SnO2 thin films with an increase in Ce concentration were observed in this study.