A channeling study of lead submonolayers deposited onto Cu(100)

• Published in: Surface science 1996-09, Vol.365 (2), p.285-296
• Main Authors: Robert, S., Cohen, C., L'Hoir, A., Moulin, J., Schmaus, D., Barthes-Labrousse, M.G.
• Format: Article
• Language: English
• Subjects: Adsorption; Applied sciences; Channeling; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Lead; Metals. Metallurgy; Physics; Solid surfaces and solid-solid interfaces; Submonolayer; Surface relaxation; Surface structure; Surface structure and topography; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(96)00717-0

We have studied the location of Pb atoms on Cu(100) at submonolayer coverages using a few hundred keV He + ion beams in channeling experiments under single- and double-alignment geometry. Different shadowing effects of Pb on Cu are experimentally observed according to the structure of the deposit, which was evidenced by LEED (in particular the c(5√2 × √2)R45° and c(2 × 2) structures). These effects disappear around the melting temperature of the structures. For a Pb coverage of θ ≈ 0.5, when a c(2 × 2) structure is formed, the distance d Pb between the Pb plane and the first (100) Cu plane, measured under double alignment geometry (channeling along [100], blocking along [110] 45° off the normal to the surface), is d Pb = 2.05 ± 0.05 A ̊ . We also find that the Pb atoms induce a static disorder in the first Cu surface plane. This disorder may be described by isotropic Gaussian displacements of Cu atoms, with a one-dimensional projected RMS deviation u d of around 0.12 Å. It depends little on the Pb structure: in particular, there is no specific disordering in the alloyed state corresponding to low Pb coverages. From this observation, we deduce that for low coverage, the Pb atoms lie about 1 Å above the first Cu plane.