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Deposition dynamics and chemical properties of size-selected Ir clusters on TiO2

Summary: Deposition dynamics and chemical properties of size-selected
Ir clusters on TiO2
Masato Aizawa, Sungsik Lee, Scott L. Anderson *
Department of Chemistry, University of Utah, 315 S. 1400 E. RM 2020, Salt Lake City, UT 84112-0850, USA
Received 2 April 2003; accepted for publication 19 June 2003
We report a study of Irn/TiO2 samples prepared by size and energy-selected deposition of Irş
n (n ¼ 1, 2, 5, 10, 15) on
rutile TiO2(1 1 0) at room temperatures. The Ir clusters are found to be formally in the zero oxidation state, and there
are no significant shifts in Ir 4f binding energy with cluster size. Over a wide range of impact energies, both Ir XPS
intensity and peak position are constant, indicating constant sticking coefficient, and no impact-driven redox chemistry.
Low energy ion scattering spectroscopy (ISS) suggests that the deposited Ir clusters remain largely intact, neither
fragmenting nor agglomerating, and retaining 3-D structures for the larger sizes. For impact energies above 10 eV/
atom, comparison of ISS and XPS data show that the Ir clusters are penetrating into the TiO2 surface, with the extent of
penetration increasing with both per atom energy and cluster size. Temperature programmed desorption (TPD) of CO
is used to further characterize the deposited Irn. This system shows pronounced substrate-mediated adsorption (SMA)
in low CO exposures, with strong dependence on cluster size. ISS and sputtering experiments indicate that CO adsorbed
via SMA is bound differently than CO adsorbed in high dose experiments. In experiments with sequential C16
O and


Source: Anderson, Scott L. - Department of Chemistry, University of Utah


Collections: Energy Storage, Conversion and Utilization; Materials Science; Chemistry