Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 36: Postersitzung (Elektronische Struktur, Grenzfl
äche fest-flüssig, Halbleiteroberfl
ächen und -grenzfl
ächen, Nanostrukturen, Oberfl
ächenreaktionen, Teilchen und Cluster, Struktur und Dynamik reiner Oberfl
ächen)
O 36.27: Poster
Montag, 7. März 2005, 15:00–18:00, Poster TU F
Surface conductance at metal-semiconductor transitions induced by alkali metal adsorption on Si(001) — •E.P. Rugeramigabo, A.A. Shklyaev, Liu Hong, V. Zielasek, and H. Pfnür — Universität Hannover, Institut für Festkörperphysik, Abteilung Oberflächen, Appelstr. 2, 30167 Hannover
Electrical transport in ultrathin Na and Cs layers on Si(001) has been studied combining macroscopic conductivity measurements with LEED, EELS, and measurements of the work function. EELS has previously identified metal-semiconductor transitions during alkali metal deposition on Si(001) at the occurence of first ordered structures in the submonolayer regime, while at room temperature (RT) only for Cs/Si(001) the transition back to a metallic surface was observed at saturation coverage. In fact we find that the conductance (σ) of the n-type substrate decreases during Na/Si(001) deposition when the first ordered adsorbate structure is observed by LEED, while for Cs/Si(001) a channel for electrical transport in surface states opens up at 0.5 ML coverage, leading to an increase of the surface conductance in the 10−5 Ω−1 range. Its dependence on temperature indicates that electrical transport is thermally activated. Upon Cs deposition at temperatures below 200 K a structural transition to a stable monolayer configuration is found to be related to the sudden onset of a metal-like conductance in the 10−3 Ω−1 range. While σ exhibits a similar onset during RT deposition beyond 0.5 ML, it decreases after finishing deposition, indicating the existence of a supersaturation Cs fraction during deposition and a relaxation of the Cs/Si(001) surface to a saturation coverage below 1ML.