Studies of Alloy Surfaces by Low-Energy Ion Scattering

Abstract

Low energy ion scattering (LEIS) techniques have been used to study the initial interaction of oxygen with Ni₃Al(100) and Ni₃Al(110), and the structure of Cu/Ru(0001). Dosing Ni₃Al(100) and Ni₃Al(110) surfaces with oxygen at a low pressure of 2 × l0⁻⁷ mB at 700°C resulted in the formation of an aluminium oxide. This oxide A10_x film was examined by measuring the azimuthal angle dependence of the scattered ion yield at fixed scattering angle under different coverages of oxygen. The results indicated that oxygen adsorption was accompanied by significant changes in the surface composition and that oxide growth proceeded by the formation of island, with the oxide layer disordered with respect to the underlying single crystal substrate. Using 1 keV Li⁺ ion scattering on Cu/Ru(0001), it was found that Cu grew layer-by-layer for the first two layers. Experimental results obtained by analysing the incident angle dependence associated with shadowing of Ru by Cu confirmed that the first overlayer Cu was in a normal registry position, i.e. there was a continuation of the hep stacking sequence. The second layer Cu atoms have also been determined to be at the fee sites by analysing the shadowing critical angles for the second layer Cu focusing onto the first layer Cu atoms in the [1O$\bar 1$ O] azimuth.