Low-energy electron diffraction observations of the thermal evolution of 0.5–3.0 ML Pt/Ni(111)

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Abstract
The near-surface geometric structure of the system 0.5–3.0 ML Pt/Ni(111) has been monitored with low-energy electron diffraction (LEED) as a function of annealing treatment. In this coverage range a variety of structures are documented. Evidence is presented for commensurate submonolayer Pt (despite the large misfit) and incommensurate (but aligned) second and third layer Pt, at low temperatures. The second and third layers of Pt yield (111)-type LEED patterns but with spacing at an intermediate value between Ni(111) and Pt(111). In a very narrow range of coverage and annealing treatment (1.5–2 ML PT and 673–773 K) a hexagonal satellite appears around each primary beam. These satellites are interpreted as evidence for partially rotated incommensurate second layer Pt domains. Annealing at 873 K or above of even the thickest deposits (3 ML) produces diffraction spots indistinguishable from Ni(111). Structural evidence is correlated with the thermal evolution of the surface electronic structure in the same system (using photoemission for local and macroscopic work function measurements). The photoemission results complement the LEED information and together they provide evidence for complex diffusional rearrangements even at low temperatures in this system.

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