Dresden 2006 – wissenschaftliches Programm

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O: Oberflächenphysik

O 5: Electronic structure I

O 5.7: Vortrag

Montag, 27. März 2006, 12:45–13:00, WIL A317

STM study of subsurface impurities in noble metals — •A. Weismann, M. Wenderoth, N. Quaas, and R. G. Ulbrich — Universität Göttingen, IV. Physikalisches

Isolated subsurface Co-atoms embedded in noble metals (Cu, Ag) were prepared under UHV-conditions by codeposition of host metal and impurity compound from two e-beam evaporators. Surface charge density oscillations in the vicinity of these impurities were investigated by low temperature Scanning Tunnelling Microscopy and Spectroscopy at 8K. While isotropic surface-state Friedel-oscillations around surface impurities were studied extensively in the past decade, bulk charge density oscillations have not been reported in this context. Here we show that interesting effects arise from the anisotropy of the host metals band-structure. Most prominent is the effect of electron focussing: the out-scattered wave is not a spherical wave as in the isotropic case but shows a preferential propagation in certain directions. This shapes the observed LDOS-pattern decisively. In this study we concentrate on the energy dependency of these bulk state interference patterns. We quantitatively compare the observed STM and STS data to calculations. For this we used the electrons retarded Greensfunction of the host material to describe the propagation process and calculated the surface LDOS by considering interference processes between an incoming and a scattered wave.