Article,
The structure of Pt-aggregates on a supported thin aluminum oxide film in comparison with unsupported alumina: a transmission electron microscopy study
Surf. Sci., 391 (1-3): 27 - 36 (1997)
DOI: DOI: 10.1016/S0039-6028(97)00449-4
Abstract
Platinum has been deposited from the vapor onto a sample consisting
of a thin aluminum oxide film grown on a NiAl(110) substrate wedge.
At the tip of the wedge small gamma-alumina crystallites are formed
which have also been platinum decorated. The size distribution of
the Pt aggregates on the thin aluminum oxide film is almost identical
to the one found for the support-free alumina crystallites. It is
also identical to the size distribution observed with STM under UHV
conditions in earlier experiments Th. Bertrams et al., Surf. Sci.
331-333 (1995) 1515. The present structural analysis reveals that
after Pt decoration the structure of the substrate remains unchanged.
The Pt forms flat, epitaxial islands on both substrates. The nearest
neighbor distances within the platinum aggregates have been determined
for the supported oxide as a function of particle size. For large
particles with radii greater than 20 � the nearest neighbor distance
of bulk Pt is observed. In the case of the smallest particles with
radii close to 10 � a contraction of up to 10% is detected. The contraction
of the interatomic distance appears not to be isotropic. The observed
Moir� patterns comply with the assumption that the substrate lattice
underneath the Pt aggregates does not change.
