Epitaxial metastable cubic TaN (B1-NaCl) thin films were grown on Si (001) substrates using an ultra-thin TiN (B1-NaCl) seed layer, as thin as similar to 1 nm. The TiN/TaN stacks were deposited by pulsed laser deposition and kept below 25 nm, with the TiN thickness systematically reduced from 15 nm to similar to 1 nm. Detailed microstructural studies including X-ray diffraction, transmission electron microscopy (TEM) and high-resolution TEM, and, preliminary Cu diffusion experiments all suggest that, the TiN seed layer thickness (similar to 1 nm-15 nm) has little or no obvious effects on the overall microstructure and the diffusion barrier properties of the TaN/TiN stacks. Published by Elsevier B.V.