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An A.E.S. study of S.E.E. and electron beam effects at oxygen exposed aluminium surfaces

Adem, Ercam H

An A.E.S. study of S.E.E. and electron beam effects at oxygen exposed aluminium surfaces Thumbnail


Ercam H Adem


An AES technique has been used to Investigate oxygen adsorption at clean polycrystalline aluminium surfaces. The adsorption process was found to consist of two stages: chemisorption, reached within the first 50L of oxygen exposure, is followed by an oxidation stage where a surface A12O3 like oxide is formed. Saturation coverage is reached after 150L. From the adsorption profile, an initial sticking coefficient of ~- 0.02 has been
In electron beam effect experiments the surface was exposed to oxygen (0 - 1000L) and the surface irradiated with electron beams of energy 1500 eV and current densities of 10-3 - 10-4 A/cm2 for > 90 minutes. The predominant beam effect observed was decomposition of surface oxide, with subsequent desorption of oxygen via the Coulomb explosion mechanism proposed by Knotek and Feibelman. From the decay of AES peak-peak heights an effective total desorption cross-section of 5 x 10“^® cm^ has been estimated.
In SEE as studied by the total yield ? versus Ep method, for the very early stages of oxygen coverage (< 15 L) a previously unreported small minima in the development of has been observed. This has been interpreted as mainly due to a reduction in the plasmon decay contribution to SEE via single electron excitations from the conduction band, and to the attenuation of plasmon loss peaks as revealed in ELS. Recent theories and calculations on SEE by Chung and Everhart, and Rosier and Brauer have indicated this contribution to be very important.
With increased oxygen coverages (> 15L), SEE from the surface is enhanced for all Ep. This has been interpreted as due to the presence of monolayer thickness Al2O3 like oxide which modifies the electronic band structure of the surface resulting In Increased effective escape depth of secondary electrons.
An extensive critical review of previous literature on A1 surfaces covering adsorption, electron beam effects and SEE studies has also been given.


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