The favourable Cu-substrate interactions on the 25% Co-doped surface, along with minimal surface rearrangements due to the lack of possible Co-Co interactions in the surface layer, make it a promising candidate for a combined barrier/liner material -we see migration of only a small number of Cu atoms into a second layer during the relaxation and the aiMD at 500 K, indicating that it should inhibit formation of 3D islands. Meanwhile, 25% W doping does not improve the binding energy of Cu compared to TaN, but it improves the Cu-substrate interaction significantly compared to the other W-doped TaN surfaces. This leads to 2D Cu structures, however the inferior adhesion of Cu and the wire-like structures formed may not be favourable for the manufacturing process.