Interfacial strain evolution and abnormal Poisson's ratios in Al nuclei for the Al/TiB2 heterostructure

The interfacial lattice mismatch and local elastic strains of Al/TiB2 heterostructures are quantitatively investigated by aberration-corrected transmission electron microscopy. Both in-plane atomic expansion and out-ofplane compression of Al layers stacked on (0001)TiB2 are uncovered and favor the further extension of deformed Al layers for realizing a successfully heterogeneous nucleation. These lattice strains can persist up to several Al atomic layers from the topmost (0001) surface of TiB2. Based on the compressive and expansive elastic strain relation, we estimate the Poisson's ratio in Al nuclei and find that large mismatch strains lead to abnormal changes in the Poisson's ratio. This study reveals the effect of lattice mismatch on the heterogeneous nucleation of Al on TiB2 and may have important implications in understanding the heterogeneous nucleation of Al.