Alloying and Structure of Ultrathin Gallium Films on the (111) and (110) Surfaces of Palladium

Growth, thermal stability, and structure of ultrathin gallium films on Pd(111) and Pd(110) are investigated by low-energy ion scattering and low-energy electron diffraction. Common to both surface orientations are growth of disordered Ga films at coverages of a few monolayers ( T = 150 K), onset of alloy formation at low temperatures ( T ≈ 200 K), and formation of a metastable, mostly disordered 1:1 surface alloy at temperatures around 400-500 K. At higher temperatures a Ga surface fraction of ∼0.3 is slightly stabilized on Pd(111), which we suggest to be related to the formation of Pd 2 Ga bulk-like films. While on Pd(110) only a Pd-up/Ga-down buckled surface was observed, an inversion of buckling was observed on Pd(111) upon heating. Similarities and differences to the related Zn/Pd system are discussed.