ADSORPTION AND DESORPTION OF OXYGEN AND NITROGEN ON PDCU(110) SINGLE-CRYSTAL ALLOY SURFACES

LEED, AES and TDS were used to study the chemisorption of oxygen and n itrogen on specially prepared Pd-rich alloy surfaces. Cu/Pd ratios of less-than-or-equal-to 0.4 were determined by AES for a four-layer surf ace region (SR); the top layer (TL) composition was approximately 100% Pd, obtained by CO TDS as characterisation method. This enabled the a verage ratio of Cu/Pd in the next three subsurface layers (3SSL) to be evaluated. Oxygen and nitrogen were adsorbed at 115 K and TDS were ob tained for temperatures up to approximately 500 K. Oxygen desorption f rom the alloy surfaces showed one peak at 144 K. The TDS saturated at approximately 9 L. Different types of adsorbate structures were obtain ed depending on the Cu/Pd (SR) ratio and the lattice type (fcc or bcc) . Oxygen adsorption on the (1 x 1) clean,surface developed two structu res, depending on the ratio of the Cu/Pd (SR). For values less-than-or -equal-to 0.1, a c(2 x 4) structure appeared at room temperature (RT), while a reconstructed (1 x 2) pattern appeared at 120 K for a Cu/Pd ( SR) of approximately 0.4. Nitrogen adsorption on surfaces with a Cu/Pd (SR) of less-than-or-equal-to 0.1 showed only a (1 x 1) surface struc ture. TDS of nitrogen with one maximum at 130 K saturated at approxima tely 1 L.