Electron beam dissociation of CO and CO2 on ZnS thin films

The effects of electron bombardment in 10−6 Torr CO or CO2 upon the surface composition of ZnS thin films was determined with Auger electron spectroscopy. The ZnS surface composition was stable in 1×10−9 Torr residual vacuum or for CO and CO2 exposures without electron bombardment. With electron bombardment and CO both present, C was deposited and S decreased, but no O accumulated on the surface. This was interpreted as an electron beam stimulated surface reaction in which CO was dissociated by the electron beam CO2 was reformed leaving C on the surface. For CO2, both C and O were increased on the surface while S was reduced. This was interpreted as a surface reaction involving dissociation of CO2 with reformation of COx leaving both C and O on the surface. The data suggest that the surface dissociation of CO2 did not occur when the sample temperature was increased from 30 °C to 150–200 °C. At 300 °C, S diffused from the ZnS substrate to the surface. The consequences of these reactions on ZnS cathodoluminescent phosphors are discussed.