Degradation of ZnS field-emission display phosphors during electron-beam bombardment

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Abstract
Phosphor thin films of ZnS:Mn on Si(100) have been subject to electron bombardment (0.6–4 keV) over a range of pressures from 1×10−6 to 5×10−8 Torr. Various gases including hydrogen, oxygen, and water vapor were introduced into the ambient during bombardment, to assess their effects on the phosphor surface. Auger electron spectroscopy data indicate that electron bombardment in the presence of O2 and H2O caused depletion of sulfur and accumulation of oxygen on the surface. Hydrogen also caused depletion of sulfur. Removal of sulfur was shown to be consistent with electron-beam dissociation of molecular species to atomic hydrogen and/or oxygen, followed by a surface reaction to form high vapor pressure sulfur compounds (e.g., SOx and H2S). In the case of oxygen and water vapor, ZnS was converted to ZnO or ZnSO4. These changes in surface chemistry reduced the intensity of cathodoluminescence from ZnS-based phosphors. The mechanisms leading to loss of CL intensity are discussed.

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