
Abstract
The ordered overlayer structures formed by Cs adsorbed on a Ru(0001) surface were analyzed by use of low-energy electron diffraction (LEED). The phase diagram reflects the dominance of dipole-dipole repulsions between the adparticles and comprises quasiliquid configurations characterized by diffraction rings up to a coverage Θ=0.17, followed by a (2×2) structure with maximum intensity of the diffraction spots at Θ=0.23. Beyond Θ=0.25, a series of structures with rotated unit cells is identified which are followed by a (√3 × √3 )R30° structure around Θ=0.33 (≊completion of the first monolayer). In the (2×2) phase the Cs atoms are located in on-top sites with a Ru-Cs bond length of 3.25±0.08 Å, corresponding to a hard-sphere radius of 1.9 Å for the Cs atom. In the (√3 × √3 )R30° structure, on the other hand, the adatoms occupy threefold hollow hcp sites with Ru-Cs bond lengths of 3.52±0.02 Å, corresponding to a Cs hard-sphere radius of about 2.2 Å. The increase in bond length and effective radius of the adparticle is paralleled by the transition of the character of bonding from more ‘‘ionic’’ at Θ=0.25 (large dipole moment) to more ‘‘metallic’’ at Θ=0.33 (dipole moment reduced by about 30%). The associated change of the type of adsorption site (from on-top to hollow) is qualitatively rationalized by a model according to which inherently less favorable sites may become preferred due to improved effective screening of the dipole-dipole repulsion by the location of substrate atoms in the region between neighboring adatoms.
Item Type: | Journal article |
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Faculties: | Geosciences > Department of Earth and Environmental Sciences > Crystallography and Materials Science |
Subjects: | 500 Science > 550 Earth sciences and geology |
URN: | urn:nbn:de:bvb:19-epub-5821-6 |
Language: | English |
Item ID: | 5821 |
Date Deposited: | 25. Aug 2008, 15:32 |
Last Modified: | 04. Nov 2020, 12:48 |