Energetics and interdiffusion at the Cu/Ru(0001) interface: density functional calculations.

Density functional theory calculations were performed on the energetics of an adatom and adlayer of Cu on a Ru(0001) slab and on the interdiffusion of Cu or Ru at the interface of Cu/Ru(0001) slab. The total energy calculations showed the equal possibilities of both pseudomorphic hcp- and fcc-adlayers of Cu on the Ru(0001) slab. The formation energies of mono-vacancy at the Cu/Ru(0001) interface and the barrier energies of the vacancy-mediated interdiffusion were calculated. The formation energies of mono-vacancy at the Cu/Ru(0001) interface were determined to be 1.31 eV for Cu atom and 1.83 eV for Ru atom, respectively. The diffusion of Ru atom into the vacancy of Cu across the Cu/Ru(0001) interface required energy increase of 0.98 eV, and the barrier energy was substantially high, 1.80 eV. On the other hand, the diffusion of Cu atom into the vacancy of Ru across the Ru/Cu(0001) interface was favored with the energy reduction of 0.35 eV. However, under this most favorable situation, the barrier energy is 0.52 eV. The calculation results imply that, as far as energetics is concerned, the diffusion of both Cu and Ru atoms via the vacancy-mediated diffusion mechanism at the Cu/Ru(0001) interface seems rather restricted unless considerable thermal activation is provided.