Layer-by-layer surfactant-induced growth of Ag on Cu(1 1 1): an impact collision ion scattering spectroscopy and scanning tunnelling microscopy study

We have investigated the structure of Ag/Sb/Cu(1 1 1) surfaces by using time-of-flight impact collision ion scattering spectroscopy. Also, scanning tunneling microscopy measurements were used in studies of the topmost layers of thin film heteroepitaxy systems at room temperature. It was found that on a surface pre-covered with a 0.2 and 0.4 ML of deposited Sb, the (1) Ag(1 1 1)[1 1 2̄]//Cu(1 1 1)[1 1 2̄] versus (2) Ag(1 1 1) [1̄ 1̄ 2]//Cu(1 1 1)[1 1 2̄] modes of Ag layers become 50% versus 50%. These ratios are much different from deposition of Ag on clean Cu(1 1 1) surfaces. Furthermore, for 0.4 ML of Sb pre-covered Cu(1 1 1), the outermost first-layer of Ag atoms shift from fcc- to hcp-sites (only the top layer of Ag atoms occupies hcp-sites). In addition, for this case, a Ag(1 1 1)(√3×√3)R30°-Sb surface forms on top of the first Ag layer. For both 0.2 and 0.4 ML coverages, Sb atoms are transported to the next growing Ag layer during subsequent Ag deposition. Sb atoms displace up to 1/3 of the first-layer of Ag atoms and are incorporated into first-layer Ag atom sites with an outward displacement of 0.2 Å with respect to Ag atoms in the first layer. With a pre-coverage of Sb atoms, Ag(1 1 1) planes prefer to grow as type (2) mode between 300 and 633 K. This growth behavior of Ag(1 1 1) planes is different from that shown previously without Sb pre-coverage on Cu(1 1 1).