Scanning tunneling microscopy study of growth of Pt nanoclusters on thin film Al2O3/NiAl(100)

Dehydrogenation of Cyclohexene on Platinum Nanoclusters on a Thin Film of Al2O3/NiAl(100)

“…Morphologies and size distributions of the Pt clusters manifested by STM are similar to those observed earlier [19]. Randomly distributed Pt nanoclusters, with a mean diameter of 2.25 nm and height of 0.4 nm (standard deviation 0.5 nm for the diameter distribution and 0.15 nm for the height distribution), are seen to grow on a crystalline Al 2 O 3 surface at any temperature in a range 300-600 K and at any coverage less than the coalescence level.…”

“…Randomly distributed Pt nanoclusters, with a mean diameter of 2.25 nm and height of 0.4 nm (standard deviation 0.5 nm for the diameter distribution and 0.15 nm for the height distribution), are seen to grow on a crystalline Al 2 O 3 surface at any temperature in a range 300-600 K and at any coverage less than the coalescence level. The proportion of large clusters is enhanced at a large coverage, up to 2 ML, or growth temperature, up to 600 K, whereas the size of most clusters remained about the mean [19]. The inset of Fig.…”

“…Both BE and FWHM results thus indicate that Pt at a small coverage is more reactive for the hydrocarbon decomposition. As the cluster size and morphology vary insignificantly with the coverage [19], the variability of the reactivity might arise not solely from the variation of the cluster morphology: the reactivity might involve the oxide support. A comprehensive answer to this question requires further investigation.…”

“…All experiments were conducted in UHV chambers with base vacuum better than 1 · 10 -9 torr. The deposition of Pt and the growth of a h-Al 2 O 3 thin film on NiAl(100) were performed as described previously [19][20][21][22]; the only difference is that the Al 2 O 3 thin film on NiAl(100) was not subjected to protracted annealing post oxidation, thus preventing NiAl facets becoming exposed on the surface [21,22].…”

“…The Pt clusters were formed by vapor deposition; their morphologies and crystallinity were characterized with a scanning-tunneling microscope (STM) and reflection high-energy electron diffraction (RHEED), respectively [19,20] [20]. We investigated the temperature dependence of the cyclohexene dehydrogenation by increasing the sample temperature in a stepwise manner and recording a photoelectron spectrum from the reaction mixture on the surface at each temperature step.…”