Ag/Cu(111) surface structure and metal epitaxy by impact-collision ion-scattering spectroscopy and scanning tunneling microscopy

Abstract

We have investigated the growth of 3 monolayers (ML) of Ag on Cu(111) for substrate temperatures from 170 through 640 K by using time of flight-impact collision ion scattering spectroscopy (TOF-ICISS). Also, scanning tunneling microscopy (STM) topographs were taken after the deposition of 0.8 ML of Ag atoms at room temperature (RT). We observed that for deposition of Ag at substrate temperatures above 300 K, two different types of epitaxial growth exist: $\mathrm{Ag}[112\ifmmode\bar\else\textasciimacron\fi{}]\ensuremath{\parallel}\mathrm{Cu}[112\ifmmode\bar\else\textasciimacron\fi{}]$ (type-n) and $\mathrm{Ag}[\overline{11}2]\ensuremath{\parallel}\mathrm{Cu}[112\ifmmode\bar\else\textasciimacron\fi{}]$ (type-r). The growth modes of the Ag thin films on Cu(111) surfaces depend strongly on the temperature during deposition with the Ag(111) planes having a preferred orientation of either type-n growth mode or type-r growth mode as a function of the Cu substrate temperature. A part of the first-layer Cu atoms (20% of the surface) is displaced at low Ag coverage, where the stacking changes abruptly from fcc to hcp sites because of the Ag atom deposition at 603 K. The STM image of the Ag coverage of 0.8 ML showed a periodic array of triangular misfit dislocation loops at the deposition temperature of RT. The triangular shape in a localized region where the stacking {Ag---Cu (A)---Cu (B)---Cu (C)} is replaced by {Ag---Cu (C)---Cu (B)---Cu (C)} in the first substrate plane. At 603 K, surface alloying of the Ag--Cu system was confirmed for Ag coverage below 0.15 ML. The experimental results concerning Ag/Cu(111) show many similarities to those in the previous study of Au/Ni(111). This would suggest that observed oscillations in the growth mode, dependent on the substrate temperature during deposition, may be a general phenomenon on solid surfaces, in cases of large misfit since it has now been seen for both Au/Ni(111) and Ag/Cu(111) systems. Furthermore, Cu atoms deposited on the Ag/Cu(111) system form islands with the same orientation of Ag(111) planes. The Cu atoms undergo surface diffusion at room temperature in the direction of type-n domains for both type-r and type-n modes Ag substrates.