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

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