Diffusion in evaporated films of magnesium-aluminium

VACUUM deposition can easily produce metal films of uniform thickness. When two such metal films are deposited, one over the other, and the resultant double layer film is annealed , diffusion will occur at the common interface, resulting in the formation of either
a solid solution or intermetallic compounds or both.
The presence of the diffusion layers can be confirmed
by electron -diffraction or X-ray diffraction or deduced from other measurements , such as electrical resistance
or adhesion ( Weaver and Hill, 1959).
These methods can give only a qualitative picture
and cannot normally give the rate of growth of the diff-usion layer and hence the diffusion coefficient of the
system . Techniques used for determining diffusion coefficients in bulk diffusion couples are inapplicable
to the study in evaporated thin films, since it is imp-ossible to section them, and the quantity of material available is not sufficient for chemical analysis. In thin films it is much more convenient to measure the
time required for one film to be completely penetrated
by atoms of the other metal. This can be done simply by measuring the variation of reflectivity with time and
this technique has been used by Schopper (1955)2 for
study of diffusion of lead into gold and by Weaver and Browne (1962, 1963, 1968 ) for study of diffusion in evaporated film of gold-aluminium , gold-lead and silver-aluminium.