Atomistic simulations on the tensile debonding of an aluminum-silicon interface
In this paper we present Modified Embedded Atom Method (MEAM) simulations of the deformation and fracture characteristics of an incoherent interface between pure FCC aluminum and diamond cubic silicon. As a first approximation, the study only considers the normal tensile separation of a  interface with the principal crystallographic axis of the aluminum and the silicon aligned. The MEAM results show that the relaxed interface possesses a rippled structure, instead of a planar atomic interface, and such ripples act as local stress concentrators and initiation sites for interfacial failure. The stress-strain (traction-displacement) response of aluminum and silicon blocks attached at an interface depends on the distance from the interface that the boundary conditions are applied, i.e. the size of the atomic blocks, and the location of the measured opening displacement. Point vacancy defects near the interface are found to decrease the maximum normal tensile stress that the interface can support at a rate almost linearly proportional to the number fraction of the dispersed defects. A crack-like vacancy defect in the bulk aluminum or silicon must reach an area fraction (projected to the surface normal to the tensile axis) of about 50 or 30%, respectively, in order to shift the failure from the interface to the bulk materials. It is further demonstrated that the present results are consistent with continuum-based traction separation laws, provided that the opening displacement is measured near the physical boundary of the deforming cohesive zone (±10 angstroms from the boundary of the Al-Si interface). As the opening displacements are measured farther from the interface, the traction-displacement response approaches that of classical linear elastic fracture mechanics.
Gall, K; Horstemeyer, MF; Van Schilfgaarde, M; Baskes, MI
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