Growth and sintering of Pd clusters on α-Al2O3(0001) -: art. no. 064712

The growth and sintering of Pd nanoparticles on alpha-Al2O3 (0001) have been studied by noncontact atomic force microscopy (NC-AFM), low-energy ion scattering spectroscopy (LEIS), temperature-programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). This is the first study of metal nanoparticles on a well-defined oxide surface where both NC-AFM and LEIS are used for characterization. These prove to be a powerful combination in assessing particle dimensions. The clean alumina surface showed atomically flat, 200-700 nm wide terraces. The sharp step edges are straight (within our resolution) for lengths of >300 nm and have heights in multiples of 0.2 nm. The Pd grows initially as two-dimensional (2D) islands at 300 K, with the transition to 3D particle growth at 0.25 ML (ML=monolayers). Upon heating at 1 K/s, the Pd starts to sinter below 400 K, and sinters at a nearly constant rate with increasing temperature, covering similar to50% less of the alumina surface by similar to1000 K, with a doubling in particle diameter and an eightfold decrease in particle number density. By,1000 K, the number density was similar to9x10(11)/cm(2) for 0.8 ML of Pd, with an average diameter of 5 nm and an average thickness of 1 nm. (C) 2005 American Institute of Physics.