Diffusion barriers for Ag and Cu adatoms on the terraces and step edges on Cu(100) and Ag(100): An ab initio study

We present the results of density-functional-theory-based calculations for the activation energies for the diffusion of adatoms (Cu or Ag) on Cu(100) and Ag(100) with and without steps. We find that only for Cu on Ag(100), exchange is the dominant mechanism for the diffusion on terraces. On the other hand, for diffusion at step edges, exchange is the dominant mechanism except for Ag on Cu(100). This result also indicates that incorporation of Cu atoms into the step edges of Ag(100) costs only 330 meV, while the energy cost for Ag incorporation into Cu(100) step edge is much higher (about 700 meV). We find the hierarchy of Ehrlich-Schwoebel barriers to be: 170 meV for Ag on Cu(100); 60 meV for Cu on Cu(100); 20 meV for Ag on Ag(100), and -30 meV (-270 meV) for Cu on Ag(100). These barriers point to a striking difference in the growth modes for Ag layers on Cu(100) and Cu layers on Ag(100).