An X-ray Study in High Vacuum of the Structure of Evaporated Copper Films

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Abstract
Films of metallic copper which have been deposited on a glass substrate at - 183°C in a high vacuum to a thickness of 2000 Å are shown to consist of aggregates of randomly oriented micro-crystallites of nominal size 40 Å, this dimension being reproducible and almost independent of the nature of the substrate at this temperature. If the films are annealed to room temperature in a vacuum which precludes the chemisorption of oxygen or other reactive gas, there is a large, rapid and irreversible increase in the nominal particle size to at least 400 Å. The chemisorption of a saturated monolayer of oxygen at - 183°C before the annealing takes place, however, almost completely prevents this re-crystallization and the particles grow to only 60 Å. The corresponding chemisorption of a smaller quantity of oxygen, sufficient only to give a small but appreciable fraction of a monolayer, inhibits the annealing process and can prolong it for several days. It does not, however, prevent the film from re-crystallizing to almost the same extent as in the complete absence of oxygen. These results are shown to be in qualitative agreement with resistivity and gas adsorption data for copper films, and their bearing on the problem of establishing a model for the structure and behaviour of evaporated metallic films is outlined. The experiments as a whole indicate that surface diffusion plays a leading part in the re-crystallization of the disordered films. Some further experiments on the effect of residual air on the structure of copper films deposited at room temperature are described, and the design of a low temperature high vacuum x-ray focusing camera, which was constructed entirely of glass and used for the above experiments, is also discussed.

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