SURFACE PHASE TRANSITION AND KINETICS OF Cu3Au (111)

Overview & Synopsis

Using glancing angle x-ray scattering techniques we have investigated the order-disorder transition of Cu3Au close to a (111) surface. The 5000Å thick Cu3Au film was grown epitaxially on a sapphire (11[MATH]0) substrate with a Nb buffer layer. The experiments were made as a function of both temperature and angle of incidence, the latter determining the penetration depth. Upon approaching the disordering temperature, radial scans of the (1[MATH]0) superstructure reflection exhibit non-classical line shapes consisting of a superposition of two Gaussian components. This profile indicates that close to the surface small disordered clusters may coexist with larger ordered domains, which is much different from the bulk behavior. In addition, quenching experiments from above to various temperatures below the ordering temperature showed that the bulk orders before the surface does and that the development of a single or double component line shape depends on whether the quench is deep or shallow.