Adsorption and desorption of oxygen and nitrogen on PdCu(110) single crystal alloy surfaces

Abstract

LEED, AES and TDS were used to study the chemisorption of oxygen and nitrogen on specially prepared Pd-rich alloy surfaces. Cu Pd ratios of ⩽ 0.4 were determined by AES for a four-layer surface region (SR); the top layer (TL) composition was ~ 100% Pd, obtained by CO TDS as characterisation method. This enabled the average 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 obtained for temperatures up to ~ 500 K. Oxygen desorption from the alloy surfaces showed one peak at 144 K. The TDS saturated at ~ 9 L. Different types of adsorbate structures were obtained depending on the Cu Pd (SR) ratio and the lattice type (fcc or bcc). Oxygen adsorption on the (1 × 1) clean surface developed two structures, depending on the ratio of the Cu Pd (SR). For values ⩽ 0.1, a c(2 × 4) structure appeared at room temperature (RT), while a reconstructed (1 × 2) pattern appeared at 120 K for a Cu Pd (SR) of ~ 0.4. Nitrogen adsorption on surfaces with a Cu Pd (SR) of ⩽ 0.1 showed only a (1 × 1) surface structure. TDS of nitrogen with one maximum at 130 K saturated at ~ 1 L.