The initial stages of epitaxial growth of (111) Ag on (111) Cu

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Abstract
The initial stages of the structural accommodation of epitaxial (111) Ag films grown on (111) Cu by vacuum evaporation were investigated using in situ U.H.V.-RHEED techniques followed by TEM and TED carried out on the same specimens. Overgrowths with average thicknesses ranging from 1 to 20 Å were studied. It was shown that film growth proceeded by a flat, stepped island type mechanism rather than monolayer by monolayer, as had been thought previously. Misfit dislocations are present in the earliest stages of film growth, as expected on the basis of the relatively large natural misfit of 13% between Ag and Cu. Three different kinds of misfit dislocations were observed. Their Burgers vectors are of the following types. b I=a/2 〈110〉, b II = a/2 〈110〉, and b III=a/6 〈121〉. Only types II and III had Burgers vectors in the (111) interface plane. The spacings of these dislocations are at least an order of magnitude larger than predicted by the theory of Frank and van der Merwe. Their presence was interpreted in terms of Matthews’ theory of coincidence lattice misfit dislocations. The elastic strains in the Ag overgrowths also were measured and compared with the calculations of van der Merwe and Ball. Good agreement between theory and experiment suggests that the closely spaced perfect lattice misfit dislocations predicted by the theory of Frank and van der Merwe are actually present at the Ag-Cu interface (in addition to the observed coincidence lattice misfit dislocations). However, the former are not detectable because of lack of resolving power in the electron microscope and the overlapping of the extended strain fields that these dislocations would be expected to have.

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