Surface-Induced Order Observed on a Cu₃Au(001) Surface

Abstract

The possibility of surface effects on the first-order transition was first proposed by Lipowsky [1]. At temperatures away from the bulk transition, the surface can exhibit disordering (if approached from below the transition) or ordering (if approached from above the transition) phenomena. So far most experimental studies on surface-induced transition have been centered on the surfaces of a classical binary alloy, Cu₃ Au [2–4]. In the case of the Cu₃ Au (001) surface, previous LEED and x-ray studies [2,3] suggested that a surface-induced disorder took place below the bulk transition. These results also indicated that the surface transition observed was consistent with a critical wetting. Recently, we studied the surface of a 2% Au-rich Cu₃ Au sample (T_c ∼ 376 °C) and found a very strong surface segregation effect [5]. Such effect produces a segregated Cu₃ Au layer at the surface with its order-disorder temperature ∼ 390 °C (i.e., close to the bulk T_C). We therefore re-investigated a second crystal, of which the stoichiometry is Cu₃ Au to our experimental accuracy. In contrast to previous studies [2,3], our results showed a surface-induced order on this sample.