Adhesion of metal on metal.: The Pt on Co case

The adhesion of Pt overlayers in pseudomorphic epitaxy on hcp Co(0001) and fcc Co(100) was investigated with first-principles calculations. This was compared to the adhesion of the Pt surface layers on Pt(I 11) and Pt(100). We show that adhesion can be analyzed by taking into account the interplay between the chemical and structural properties at the interface. The free Pt planes with the bulk Pt-Pt distance are submitted to tensile stress which can be relaxed by 6.6% and 9.1% contraction for the (111) and (100) symmetries respectively. This results in equilibrium interatomic distances which are not far from that of the Co substrate, Consequently the stress energy in a pseudomorphic Pt monolayer on a Cc substrate is lower than the stress energy of pure Pt(111) or Pt(100) surfaces. However, this is at the expense of the Pt chemical reactivity towards the Co substrate. This is in agreement with the general dependence between chemical reactivity and stress of a metal surface. (C) 2001 Elsevier Science B.V. All rights reserved.