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Dislocation Emission at Surfaces

Published online by Cambridge University Press:  21 February 2011

G. E. Beltz  and
L. B. Freund
G. E. Beltz
Affiliation:
Department of Mechanical and Environmental Engineering, University of California, Santa Barbara, CA 93106
L. B. Freund
Affiliation:
Division of Engineering, Brown University, Providence, RI 02912
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Abstract

An exact expression for the elastic energy associated with a semicircular shear dislocation loop emanating from a free surface, such as that of a stressed thin film, is derived (within continuum dislocation theory) and compared with earlier approximations. The energy required to activate a semicircular dislocation loop into its unstable “saddle-point” configuration is then re-calculated, based on the modified expression for the self-energy. It is found that the shear stress necessary to emit a loop, as a function of temperature, is almost 50% less than earlier estimates. The effects of ledges on the surface, as well as loop geometry, are discussed. The principal drawback to this type of calculation is pointed out, namely, that the critical radius of an incipient dislocation loop can be on the order of one atomic spacing, which is too small for a continuum theory to be valid.

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Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 356: Symposium B2 – Thin Films: Stresses and Mechanical Properties V , 1994 , 93
Copyright
Copyright © Materials Research Society 1995

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