A STUDY OF THE CU3AU(110) SURFACE-STRUCTURE BY RHEED

The (110) surface of a Cu3Au single crystal (precise composition is Cu71.7Au28.3) has been studied by RHEED and Auger electron spectroscopy (AES) at a range of temperature in UHV. Surface compositions which result from different annealing times are measured by AES and compared with low energy ion scattering results. Stable 2 X 1 and 4 X 1 surface superstructures are observed. At temperatures lower than 190-degrees-C the surface exhibits the 4 X 1 structure, while between 190 and 374-degrees-C it has a 2 X 1 structure. We believe that these superstructures are formed by chemical ordering of the surface atoms. A tentative surface atomic model, in which the 2 X 1 structure occurs in the first layer and the 4 X 1 structure occurs in the second layer, is given. By using this model, some experimental observations can be better understood. Some possible evidence of a surface long period structure has also been observed and possible further experiments are discussed.