AVS 47th International Symposium
    Material Characterization Tuesday Sessions
       Session MC-TuM

Paper MC-TuM7
Quantification of the Changes in the Air-formed Oxide/Hydroxide Film at the Surface of Aluminium on Exposure to Ambient Conditions

Tuesday, October 3, 2000, 10:20 am, Room 207

Session: Real World Surface Analysis
Presenter: M.R. Alexander, UMIST, UK
Authors: M.R. Alexander, UMIST, UK
G.E. Thompson, UMIST, UK
G. Beamson, RUSTI, CLRC, UK
A.J. Roberts, Kratos Analytical, UK
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The performance of coated and bonded Al is dependent on its surface chemistry. XPS is a powerful tool for characterising of the surface air-formed film. It is apparent that agreement exists in the literature on the method to calculate the oxide thickness from the clearly resolved metal and oxide components of the XPS Al2p core level.@footnote 1@ However, there is no consensus on the approach for fitting the unresolved oxide and hydroxide components of the O1s, indeed some suggest that it is not advisable.@footnote 2@ Recently, a method based on defining the separation between the O1s and Al2p components has been developed using an oxyhydroxide standard.@footnote 3@ Here, the film formed at the surface of magnetron sputtered Al is characterised. Importantly, this sample allows reliable definition of the age of the surface film and control of the alloying elements. Curve fitting of the O1s and Al2p core levels from samples after a range of atmospheric exposure times revealed the gradual formation of hydroxide ions in the surface film, an increase in its thickness and the adsorption of adventitious hydrocarbon. Interestingly, it was determined that atmospheric moisture influences strongly the hydroxyl concentration and the rate of film growth. Changes in the wetting of the surface were measured through the water contact angle, which increased from about 10° to 80° over a 24-h period. This was assigned to the formation of a continuous overlayer of hydrophobic adventitious hydrocarbon onto the hydrophilic oxide/hydroxide surface film. Characterisation of this "ageing" of the Al surface forms the basis for an investigation into the effectiveness of plasma cleaning and the atmospheric stability the resultant surface. @FootnoteText@ @footnote 1@ B Strohmeier Surf. Interface Anal. 15 51 (1990). @footnote 2@ PMA Sherwood Surf. Sci. Spect. 5 (1) 1 (1998). @footnote 3@ MR Alexander, GE Thompson and G Beamson, Surf. Interface Anal., 29 (7) in press (2000).