The lateral distribution of submonolayer Pd deposited at room temperature on the surface of a polycrystalline Ni sample has been studied with scanning photoelectron microscopy (SPEM). The Ni sample consisted of differently oriented crystal grains, as evidenced by low-energy electron microscopy and micro-low-energy electron diffraction measurements and by SPEM Ni $3p$ maps showing surface topography. The elemental contrast of the SPEM Pd $3d$ images have revealed that the different grains of the polycrystalline surface show different activity, resulting in differences in the local Pd concentrations. The chemical state of Pd was well described by the Pd ${3d}_{5/2}$ spectra. They consisted of two components interpreted in terms of adsorbed Pd species (Pd ${3d}_{5/2}$ binding energy of 336.0 eV) and Pd embedded in the Ni a surface lattice, forming surface ${\mathrm{Pd}}_x{\mathrm{Ni}}_y$ alloy (Pd ${3d}_{5/2}$ binding energy at 335.5 eV). Chemical imaging in terms of these Pd ${3d}_{5/2}$ components confirmed that the ability of Pd to alloy or form clusters also depends on the individual structure of the grains on the polycrystalline Ni surface.

• Received 31 May 2002

DOI:https://doi.org/10.1103/PhysRevB.67.045411