Surface structure and metal epitaxy: impact collision ion scattering spectroscopy studies on Au–Ni(111)

Abstract

The growth mode of multi-layers of Au atoms on Ni(111) has been investigated over a wide temperature range from 170 K through 680 K by using time-of-flight-type impact collision ion scattering spectroscopy. We found that only two different types of epitaxial growth exist: Au[11 2 ̄ ]‖ Ni[11 2 ̄ ] (normal mode) and Au[ 1 ̄ 1 ̄ 2]‖ Ni[11 2 ̄ ] (reverse mode) at substrate temperatures over 300 K. Moreover, the relative amounts of these two growth modes show an observed oscillatory dependence on the growth temperature during Au deposition. Measurements for Au deposition at 500 and 625 K show that first-layer Ni atoms were shifted and localized in defined areas in which the stacking changed abruptly from ABC to ABA (hcp-sites). However, for deposition at 170 K this shift was not observed and the Au layer is close to a simple overlayer structure. Surface alloying of the Au–Ni system was confirmed for deposition at elevated temperatures in which Au atoms displace first-layer Ni atoms, with an outward displacement of 0.3 Å with respect to first-layer Ni atoms at both 500 and 625 K.