Palladium Nanocrystals onAl2O3: Structure and Adhesion Energy

Abstract

We have investigated the structure and morphology of nanosized palladium clusters supported by a thin ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ film on NiAl(110) using scanning tunneling microscopy. Well-ordered clusters with a diameter above $\ensuremath{\approx}40\AA{}$ 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 ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ we obtain a value of ${W}_{\mathrm{adh}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.8\ifmmode\pm\else\textpm\fi{}0.2\mathrm{J}/{\mathrm{m}}^{2}$. This result is at variance with values recently derived on the basis of ab initio density-functional theory.