Heteroepitaxial integration of metallic nanowires: transition from coherent to defectiveinterfaces via molecular dynamics

Abstract

We use molecular dynamics to characterize the epitaxial integration of axially heterogeneousface-centered cubic (fcc) metallic nanowires. In order to isolate the effect of lattice mismatch we focus onPt/Pt* wireswhere Pt* differs from Pt only in its lattice parameter. We characterize the critical lattice mismatchbeyond which coherent interfaces are unable to withstand the interfacial stress and defectsare introduced. We studied wires of various radii, lengths, and orientations (, and ). We find that one-dimensional structures can withstand a very large lattice mismatchwith defect-free interfaces (over 10% for wires with small radius), much larger than possible in planar geometries (thin films). Oursimulations show that the critical lattice mismatch increases with decreasingradius; this increase is very rapid for radii below about 3 nm. Surprisingly, in thissmall radius regime the critical mismatch increases with increasing wire length;this behavior is the opposite of what occurs in thin films and what we observefor wires with larger radii. We find that the critical mismatch shows a strongdependence on the orientation of the wires associated with the resolved shear stress onavailable slip systems caused by the shear present along the intersection between theinterfacial plane and the free surface, where plastic deformation nucleates. We alsoperformed a detailed characterization of the dislocations that are introducedto release the interfacial strain as a function of geometry and orientation; ouranalysis reveals a novel interfacial relaxation mechanism in wires involving interfacial dislocations of screw character.