Field ion microscopy of platinum adatoms deposited on a thin Al2O3 film on NiAl(110)

Aiming to contribute to a characterisation of the surface diffusion and clustering of individual metal adatoms on a well-characterised oxide film the feasibility of FIM investigations is demonstrated for the catalytically relevant system Pt/Al2O3/NiAl(110). A thin aluminium oxide film was grown on a [110] oriented NiAl field emitter through dissociative oxygen adsorption followed by heating cycles. The film was characterised using FEM, FES and neon FIM. Field desorption sequences revealed that the film prepared on NiAl(110)was approximately two layers thick. Below 80 K the film was stable at field-strengths applied for neon FIM. The presence of an ordered structure was suggested by FEM and FIM pattern. FIM of Pt adatoms was achieved at 79 K and below best image field strength using neon as the imaging gas. From preliminary displacement observations the surface diffusion activation energy of individual Pt adatoms was estimated and ranges between 0.4 and 0.5 eV. After three heating cycles to a maximum temperature of 230 K an ordered arrangement of Pt adatoms was noticed in the vicinity of a presumable point defect. (C) 1999 Elsevier Science B.V. All rights reserved.