Dresden 2003 – wissenschaftliches Programm
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O: Oberflächenphysik
O 20: Halbleiteroberfl
ächen und -grenzfl
ächen
O 20.8: Vortrag
Dienstag, 25. März 2003, 16:45–17:00, FOE/ANOR
Adsorbate chains of sodium on Ge(100) — •H. Pfnür1, W. Ernst1, C. Tegenkamp1, K.L. Jonas2, V. von Oeynhausen2, and K.H. Meiwes-Broer2 — 1Institut für Festkörperphysik, Universität Hannover, Appelstr. 2, D-30167 Hannover — 2Fachbereich Physik, Universität Rostock, Universitätsplatz 3, D-18055 Rostock
The adsorption of sodium on Ge(100) has been investigated in the submonolayer regime by means of STM, LEED and electron spectroscopies (XPS,UPS). Upon deposition at room temperature p(4×1) (metastable) and p(2×1) superstructures are formed, similar to the system Na/Si(100). They correspond to coverages,Θ, of 0.25 and 0.5 monolayers, respectively. Annealing and simultaneous thermal desorption of Na leads to a p(3×2) structure with Θ = 1/6 after an incommensurate state has been passed. The formation of this structure requires a rearrangement of substrate atoms which can be deduced from the modification of Ge step morphology. Further reduction of coverage results in adsorbate chains parallel to the Ge dimer rows with a distance of four, six or eight lattice constants between neighbouring chains. The lateral coupling between them is strongly anisotropic. Na chains are embedded into the surface between adjacent unoccupied dimers rows, i.e. the substrate dimers are replaced by the adsorbate. Therefore the chain structure as well as the (3×2) differ from the bare substrate with respect to the density of Ge atoms in the first layer which leads to a one–dimensional height modulation of the surface. As will also be demonstrated, Na rearranges the substrate steps of vicinal Ge(100), forming single-domain surfaces.