Metastable structures of Dy layers adsorbed on Mo(112) and their transformations |
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Authors: | A Fedorus V Koval A Naumovets H Pfnür |
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Institution: | Institute of Physics, Natl. Academy of Sciences of Ukraine, Prospect Nauki 46, UA-03039, Kyiv-39, Ukraine, UA Institut für Festk?rperphysik, Universit?t Hannover, Appelstrasse 2, 30167 Hannover, Germany, DE
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Abstract: | Ordering of dysprosium on Mo(112) up to 1.5 monolayers has been investigated by LEED and work function analysis after adsorption
at 100 K and annealing between 200 and 1000 K. At low annealing temperatures (< 350-600 K) ordered structures are found, which
are changed or even destroyed irreversibly by annealing steps to higher temperatures. At coverages, θ, up to 0.3 monolayer
a (6×1) not strictly commensurate chain structure is seen, which coexists up to θ = 0.58 with a one-dimensionally incommensurate
c( 1.56×2) structure. At higher coverages up to the physical monolayer at θ≈ 0.77, incommensurate ( n×2) followed by oblique ( n×1) structures are seen with n continuously variable with coverage. The second layer forms a p (1.33×1) structure. Annealing to higher temperatures causes
irreversible structural transitions with strongly coverage dependent properties. Up to θ = 0.58, only a glass-like disordered
phase is formed, which cannot be ordered again. In contrast, the rectangular incommensurate structures between 0.58 < θ <
0.68 remain unchanged upon annealing, whereas the structures at higher coverages and those of the second layer are transformed
into commensurate (s×1) structures with integer s. Geometrical models are presented for the non-annealed structures and possible origins for the two-dimensional concentration
dependent vitrification of the Dy layers are discussed.
Received 15 June 2001 |
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Keywords: | PACS 68 55 -a Thin film structure and morphology – 64 70 Pf Glass transitions – 61 14 Hg Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED) |
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