Coverage dependent adsorption sites in the K/Cu(100) system: A crystal truncation rod analysis

H. L. Meyerheim, I. K. Robinson, V. Jahns, P. J. Eng and W. Moritz

Abstract

The analysis of the intensity along the diffraction rods normal to the crystal surface (crystal truncation rods) has been used to analyse the adsorption sites of potassium atoms adsorbed at T = 330 K on atomically clean Cu(100) under ultra high vacuum conditions. At potassium coverages below about Θ = 0.18 ML (1 ML = 1.53 × 1015 atoms cm−2), where no ordered adsorbate superstructure forms, the potassium atoms are adsorbed in the fourfold hollow sites of the Cu(100) substrate at d1 = 2.1(4) Å above the first Cu layer corresponding to an effective potassium radius of reff = 1.5(3) Å which is close to the ionic radius of 1.33 Å. Within about 1 –2% the substrate interlayer spacings, d12 and d23 are not affected.

At high coverage (Θ ≈ 0.30 ML) where an ordered incommensurate overlayer forms, the adsorption site is partially on-top. These results are in correspondence with the model of alkalimetal adsorption on metals supposing extensive charge transfer from potassium to the substrate at low coverage.

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Zeitschrift für Kristallographie – Crystalline Materials offers a place for researchers to present results of their crystallographic studies. The journal includes theoretical as well as experimental research. It publishes Original Papers, Letters and Review Articles in manifold areas of crystallography.

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