Low-Temperature Properties of Evaporated Lead Films

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Abstract
Leadfilms have been deposited onto room‐temperature substrates having low thermal expansion coefficients and the residual mechanical stresses present in these films have been determined as a function of film thickness and film purity. At room temperature no measurable stress (<5×107 dyn/cm2) was present in any film. At 78° and 4.2°K the stress σ was given by σ=α+β/d, where α is a constant dependent on temperature and d is the film thickness. A model involving surface pinning of dislocations predicts an equation of this form, but the experimental values for the stress were found to be appreciably larger than values calculated on the basis of bulk data. The experimental values were substantiated by superconducting critical temperature measurements on films of various thicknesses. Localized crystalline growth was observed in leadfilms after cooling to 4°K. The film material around these micron‐size crystals exhibiting five‐ and sixfold rotational symmetry was thinned to the point that physical holes were evident in the thinner films. In addition, with repeated temperature cycling, extensive cross slip was observed.

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