Photoemission from Pd/Ti and Ti/Pd interfaces: dispersed metal-metal support interaction

Abstract

We present new XPS, UPS and XAES results of dispersed Ti on Pd and Pd on Ti at room temperature. Both metal evaporation and photoemission experiments were performed in a UHV system at background pressure lower then 10−10 Torr. The concentration of deposited metal for both Pd and Ti varies from 1 × 1014 atom cm−2 up to 3 × 1016 atom cm−2. Within this range of concentrations Pd 3d core lines shift by 1.2eV towards higher binding energy monotonously with decreasing cluster size; the width of Pd core lines remains constant within the accuracy of the binding energy measurements, i.e. ±0.1eV. No shift of core levels of Ti substrate and no significant change of their widths were observed. On the other hand, in the case of Ti evaporation onto a Pd sheet the substrate 3d core levels split into two lines; one remaining at the Pd clean substrate position and the other is shifted by 1.2eV for all concentrations of deposited Ti. The Ti 2p binding energy of the dispersed Ti increases monotonously from the value corresponding to the highest coverage to the one for the lowest coverage by 1.3eV. We conclude that evaporation of Ti on a Pd surface results in the formation of bimetallic islands, which is in contrast with the results of Pd dispersed on a Ti surface, where weak bonds between Pd and Ti atoms in the interface were interpreted.