ORDERING AT THE SURFACE OF CU85PD15(110)

We have investigated ordering at the (110) surface of Cu85Pd15 using s canning tunnelling microscopy (STM) and reflectance anisotropy spectro scopy (RAS). The surface is found to adopt the L1(2) structure of Cu3P d, with double atomic height steps and the exclusive existence of a te rmination by rows of atoms believed to be Cu. These rows are revealed to be imperfectly ordered on a scale to which previous diffraction exp eriments would have been insensitive. RAS revealed the presence of a f eature at about 2 eV similar to that observed on the surface of pure C u(110), which we attribute to the rows of Cu atoms on the Cu85Pd15(110 ) surface. The intensity of the RAS feature was lower than that found for the Cu(110) surface, though it developed with annealing, implying that it may be used to monitor the disorder in the Cu rows observed by STM.