Electron-Stimulated Desorption of H⁺, H₂⁺, OH⁺, and H⁺(H₂O)_n from Water-Covered Zirconia Surfaces

Abstract

Electron beam induced production and desorption of H + , H 2 + , OH + , and H + (H 2 O) n has been studied from water-covered zirconia surfaces. The proton yield is strongly dependent upon the form of water present with large yields mainly from multilayers or clusters. The high proton kinetic energy distributions and the linear yield vs dose are indicative of proton formation and desorption by 2-hole and 2-hole, 1-electron final states. These localized states are produced either directly or via Auger decay pathways, and desorption occurs from the vacuum surface interface as a result of a Coulomb explosion. The proton yield increases from 80 to 150 K and then drops dramatically as the temperature exceeds 150 K. The increased yield is associated with structural and physical changes in the adsorbed water and longer excited-state lifetimes. The decreased yield is correlated with water desorption. Above 180 K, a small proton signal is observable which we associate with electron-stimulated dissociation of hydroxyl groups present on the zirconia surface. At temperatures above 225 K, this yield drops and gives rise to electron-stimulated desorption of OH + ions. H 2 + is also formed from adsorbed water and involves direct dissociative ionization channels. Some reactive scattering of energetic protons and 2-hole Coulomb interactions produce H 3 O + and other higher mass clusters such as H + (H 2 O) n , where n ) 2-8. Though this is a minor channel, it yields information concerning 2-hole screening distances.

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“…[37][38]53 Therefore, an increase in the flux of impinging electrons should be correlated with a linear enhance of the amount of desorbed ions. [37][38]53 Therefore, an increase in the flux of impinging electrons should be correlated with a linear enhance of the amount of desorbed ions.…”

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