Stabilizing single metal adatoms at room temperature: Pd on C- and O-covered V(1 0 0)

The initial stages of Pd thin film growth on clean and C- and O-precovered V(1 0 0) surfaces at room temperature (RT) and 200 °C have been studied by means of scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). In the presence of C and O, the adsorption of Pd atoms in the clean four-fold hollow sites of the V surface is strongly preferred. Upon deposition of Pd in the submonolayer range, it was possible to stabilize single Pd adatoms and small clusters at RT. Annealing such a surface at 200 °C leads to the formation of rectangular Pd islands (size ≈40×40 Å2) and to the compression of the initial C and O adlayer in the areas between the Pd. For higher Pd coverages we found that oxygen acts as an anti-surfactant, shifting the onset of second layer growth dramatically. The reason for the change of the growth mode of Pd on V(1 0 0) from Stranski–Krastanov to a Volmer–Weber-type growth in the presence of oxygen can be found in a higher free energy of the film/substrate interface compared to the clean surface.