Phase diagram and critical behavior of the adsorption system O/Ru(001): Comparison with lattice-gas models

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Piercy, P.; De'Bell, K.; Pfnür, H.: Phase diagram and critical behavior of the adsorption system O/Ru(001): Comparison with lattice-gas models. In: Physical Review B 45 (1992), Nr. 4, 1869. DOI: https://doi.org/10.1103/PhysRevB.45.1869

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Abstract: 
The chemisorption of oxygen on the Ru(001) surface shows ordered p(2×2) and p(1×2) phases at coverages of 1/4 and 1/2 monolayer, respectively, that are observed to undergo apparently continuous transitions to a disordered state upon heating. We present here details of the experimental determination of the O/Ru phase diagram, lattice-gas models that describe it, and some (but not all) of the observed critical behavior. Monte Carlo simulations based on a phenomenological Hamiltonian describing pairwise interactions between adatoms are used to calculate the phase boundaries and (effective) critical exponents. Restricting adsorption of oxygen atoms to the triangular lattice of the hcp-type hollow sites as seen experimentally, repulsive first- and second-nearest-neighbor interactions are sufficient to describe the observed phase diagram at coverages Θ<0.4 and the four-state Pott’s-class critical exponents at Θ=1/4, but fail to describe the higher coverage region. This model is then generalized to allow oxygen adsorption on both hcp- and fcc-type hollow sites, with a difference in binding energy of 0.52 eV between the two types of sites. At higher coverages, repulsive interactions within the adsorbate lead to a spillover of up to 12% of adatoms onto the sites of higher energy, markedly reducing the transition temperature at Θ=1/2, in agreement with the experimental results on O/Ru(001). However, effective critical exponents computed for this model are near four-state Pott’s values at Θ=1/2, in contrast to the experimental data and suggestive of crossover behavior involving (2×2)-honeycomb and p(2×1) ground states.
License of this version: Es gilt deutsches Urheberrecht. Das Dokument darf zum eigenen Gebrauch kostenfrei genutzt, aber nicht im Internet bereitgestellt oder an Außenstehende weitergegeben werden.
Document Type: article
Publishing status: publishedVersion
Issue Date: 1992
Appears in Collections:Fakultät für Mathematik und Physik

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1 image of flag of Germany Germany 42 55.26%
2 image of flag of United States United States 12 15.79%
3 image of flag of China China 6 7.89%
4 image of flag of No geo information available No geo information available 2 2.63%
5 image of flag of France France 2 2.63%
6 image of flag of Brazil Brazil 2 2.63%
7 image of flag of Indonesia Indonesia 1 1.32%
8 image of flag of Hungary Hungary 1 1.32%
9 image of flag of United Kingdom United Kingdom 1 1.32%
10 image of flag of Canada Canada 1 1.32%
    other countries 6 7.89%

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