Palladium nanocrystals on Al2O3:: Structure and adhesion energy

We have investigated the structure and morphology of nanosized palladium clusters supported by a thin Al2O3 film on NiAl(110) using scanning tunneling microscopy. Well-ordered clusters with a diameter above approximate to 40 Angstrom. were imaged with atomic resolution, allowing a crystallographic identification of the cluster facets. A new method to obtain quantitative information on the work of adhesion (adhesion energy) of metal clusters deposited on oxides is introduced. For Pd on Al2O3 we obtain a value of W-adh = 2.8 +/- 0.2 J/m(2). This result is at variance with values recently derived on the basis of ab initio density-functional theory.