Münster 1999 – wissenschaftliches Programm
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O: Oberflächenphysik
O 5: Methodisches (Experiment und Theorie) (I)
O 5.1: Vortrag
Montag, 22. März 1999, 11:15–11:30, S2
Theory of STM imaging of CO adsorbed on transition metal surfaces — •D. Drakova1 and G. Doyen2 — 1University of Sofia, J. Bourchier 1, Sofia 1164, Bulgaria — 2LM-Universität München, Sophienstr. 11, D-80333 München, FRG
The theoretical models of CO adsorption on Cu and Pt single crystal surfaces reveal similar binding mechanisms, though the energies of adsorption differ significantly [1,2]. In the local density of states concept for explaning STM imaging, one would expect adsorbed CO molecules to appear as protrusions in the STM images independent of the nature of the transition metal surface. This is the case with CO/Pt(111) [3], however, CO adsorbed on Cu(111) and Cu(110) is imaged as indentation in STM experiments using clean transition metal tips [4]. We suggest a solution of this problem taking into account that in STM the system is in an excited electronic state. The dynamic relaxation processes on the CO molecule and in the metal are included. In the excited state, created by by the tunnel current, the interaction of the 2π CO-derived states with localized affinity-like metal orbitals on the lattice sites of Cu(111) leads to attenuation of the density of states of the combined system at the Fermi level and, hence, to the imaging of CO as an indentation. This effect is less pronounced in the case of CO adsorbed on Pt(111) because of the different nature of the affinity orbitals on Pt(111).
[1] G. Castro and G. Doyen, Surf. Sci. 307-309, 384 (1994).
[2] D. Drakova and G. Doyen, Surface Sci. 226, 263 (1990).
[3] J.A. Stroscio and D.M. Eigler, Science, 254, 1319 (1991).
[4] L. Bartels et al., Appl. Phys. Lett. 71, 213 (1997); B.G. Briner et al. Science, 278, 1189 (1997); M. Doering et al., Faraday Discuss. 105, 163 (1996).