SURFACE-STRUCTURE OF STEPPED NIAL(111) BY LOW-ENERGY LI+ ION-SCATTERING

Previous LEED and ISS studies have indicated that there are equal amounts of Ni and Al terminated domains on the (111) surface of the strongly ordered NiAl alloy. However, a study of the energy dependent broadening of LEED beams diffracted from a stepped NiAl(111) surface indicates that there is a preference for double step heights suggesting that high step density may impose termination in only one type of domain. We have now measured the angle dependence of Li+ scattering from stepped NiAl(111) surface cut 1.7° from the (111) orientation. Scattering along the [121] and [211] azimuths permit conditions where only the first layer or where a sum of first and second layer scattering is observed. By analysis of the Ni and Al intensities from first and second layers and comparison with previous ion scattering results on NiAl(110), it is found that the equilibrium stepped surface terminates with roughly equal amounts of both types of domains. The angle dependence of the ion scattering confirms the bulk terminated surface structure with first layer relaxation. The incidence angle associated with the onset of second layer scattering from Ni and Al can be used to determine the first inter-layer spacing for each type of domain independently. The measured spacings confirm previous LEED results for the low index surface that the first layer spacing differs in magnitude for the two different terminations. © 1990.