Ion-scattering analysis of copper films oxidized in 18O

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Abstract
Thirty-six copper films, 200 Å thick, were deposited in vacuum onto Pt, Au, and glass substrates and oxidized to CuO0.67 in 16O2 or in 98% pure 18O2. Depth profiles of the copper oxide films were obtained using ion scattering spectrometry. For 90° scattering of 3He ions, the peak separation between 16O and 18O was 0.030 in E/E0, in agreement with the value expected from the binary collision theory. The intensity distribution of the scattered ions from oxygen is Gaussian with σ of 0.0094 E/E0. The 3.2 σ separation of the peaks permitted measurement of different 18–16 O ratios of oxides grown in varying concentrations of 16O2 and 18O2. Within experimental error, the sum of the peak heights of 18O and 16O is equal to that for pure 16CuO0.67. This result, together with a measured Cu/O peak height ratio of 16.4±1.0 for the 36 films suggests isotopic labeling could be used for studying (initial) oxidation mechanisms for copper oxide. As an example, depth profiles of polypropylene coated onto 18CuO0.67 films are presented before and after oxidative degradation of the polymer in 16O2. The profile data are in agreement with a model of reduction of the oxide by the polymer and partial reoxidation of the copper formed by 16O2.
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