PROPERTIES OF PDCU(110) SINGLE-CRYSTAL ALLOY SURFACES - REVERSIBLE CHANGES OF DOMAIN SIZES

The composition of PdCu(110) single crystal alloy surfaces (bulk Pd/Cu = ? : ?) can be changed by sputtering and annealing at different tempe ratures. A survey of surface structures and compositions in equilibriu m shows the influence of Cu segregation. Samples with Cu/Pd ratios in the surface region (congruent to 4 layers) from 0.3 to 1.3 and with (? x 2) and (1 x 1) surface structures were prepared. Surfaces with simi lar to 100% Pd atoms and mixed compositions of Pd and Cu atoms (down t o similar to 70% Pd) at the top surface layer were investigated. Metho ds used for characterization were video low energy electron diffractio n for structure analysis, Auger electron spectroscopy for the surface region of similar to 4 layers depth and CO thermal desorption spectros copy for composition analysis of the top surface layer. Domain extents along [10] and [01] crystallographic directions, of surfaces with dif ferent compositions, changed reversibly when measured during sample he ating and cooling cycles. The change proceeds in a manner that depends on the sizes of domains, on the crystalline amount and on the amount of Cu in the surface region. The surface domains contain a small numbe r of lattice cells (similar to 9 to similar to 18) and a large amount of atoms in the disordered intercrystalline areas.