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Method for Obtaining Very Large Elastic Strains in Thin Films

IP.com Disclosure Number: IPCOM000088971D
Original Publication Date: 1977-Aug-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Matthews, JW: AUTHOR

Abstract

Large "biaxial strains" can be obtained by depositing thin films epitaxially onto suitable substrates. (Strictly speaking these are not "biaxial strains" but strains produced by a "biaxial stress".) For example, if palladium is deposited onto gold at room temperature, the initial palladium layer is strained by almost 5% to match the gold substrate. Although this strain is very large the thickness at which the palladium begins to relax its strain is very small (about 5Angstroms).

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Method for Obtaining Very Large Elastic Strains in Thin Films

Large "biaxial strains" can be obtained by depositing thin films epitaxially onto suitable substrates. (Strictly speaking these are not "biaxial strains" but strains produced by a "biaxial stress".) For example, if palladium is deposited onto gold at room temperature, the initial palladium layer is strained by almost 5% to match the gold substrate. Although this strain is very large the thickness at which the palladium begins to relax its strain is very small (about 5Angstroms).

One way of increasing the upper limit to the elastic strain, or to increase the thickness to which a particular strain can be retained, is to sandwich the film 10 between two crystals 12 and 14, as shown in Fig. 1. The effect of sandwiching is to double the maximum attainable strain. Also, if the thickness at which a single film on a substrate begins to relax its elastic (misfit) strain is h(c), then the thickness at which a sandwiched film will begin to relax is 2h(c).

If the sandwiched film 10, described above, is replaced by a multilayer layer sandwich of material 101 and 102 (Fig. 2), and the materials used are chosen so that the lattice parameter of the substrate matches that of the sandwich taken as a whole, then one would expect a misfit of up to 20% to be accommodated by elastic strain. This does not mean that a strain of 20% is attainable in a single layer. It means that the strain changes from +10% in layer 101 to -10...