Epitaxial growth of Cu on Ag(1 1 1) studied with angle-resolved photoemission spectroscopy

The growth of Cu on Ag(1 1 1) under varied growth conditions was investigated with angle-resolved photoemission spectra. The evolution of Cu/Ag(1 1 1) during annealing was characterized on monitoring its surface states. The surface morphology of a Cu film on Ag(1 1 1) depends on the temperature and the Cu coverage. Islands or crystalline films develop when Cu is deposited at ∼300 K. Defects in the Cu films penetrate deeply into the Ag(1 1 1) substrate and expose the Ag(1 1 1) surface. The deposition of Cu at a low temperature results in disordered films. On annealing, the films become ordered with defects. Our results show the segregation of Ag on the Cu surface, which occurs at 300 K and becomes accelerated significantly at ∼380 K. After being annealed above 430 K, all islands and films of Cu are fully covered with Ag, showing a (9 × 9) reconstruction. Our results indicate also that the segregation of Ag on the Cu surface occurs only after the Ag(1 1 1) surface is exposed, indicating that Ag atoms migrate to the Cu(1 1 1) surface, not through bulk Cu, but along the walls of the islands and the defects in the films.