Growth mechanisms of Pd nanofilms electrodeposited onto Au(111): an in situ grazing incidence X-ray diffraction study

Electrochemical deposition of ultra-thin Pd films onto Au(111) single crystals in a solution containing chloride was studied with in situ surface X-ray diffraction measurements. We report a detailed description of the growth mode, as well as film morphology and lattice parameters as a function of thickness, from 2 up to 10 monolayers (ML) as equivalent thickness. An almost ideal layer-by-layer pseudomorphic growth is observed up to two deposited ML. For higher thicknesses, it is followed by the growth of large 3D Pd bulk-like islands. They are about 20 +/- 5 ML high and similar to 220 angstrom in diameter for the Pd-4ML film and occupy only about 20% of the surface. Their height increases faster than their size with the Pd deposited amount. We could clearly show that chlorides do not play any role in inhibiting the three-dimensional growth of Pd/Au(111) films. We could also unequivocally correlate the features observed by electrochemical surface characterisation in an acidic medium with the detailed structure obtained by diffraction.