Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 40: Particles and Clusters I

O 40.5: Talk

Wednesday, March 28, 2007, 16:45–17:00, H38

The local tunnelling conductance on cobalt clusters at semiconductor surfaces — •Kristian Sell, Armin Kleibert, Viola von Oeynhausen, and Karl-Heinz Meiwes-Broer — Institut für Physik, Universität Rostock, Universitätsplatz 3, 18051 Rostock

We present scanning tunnelling spectroscopy (STS) and microscopy (STM) measurements on isolated cobalt nanoparticles with diameters ranging from 2 to 12 nm after in-situ deposition on Ge(001). The mass-filtered clusters have been deposited under soft-landing conditions (E_kin/atom < 0.5eV) using an arc cluster ion source (ACIS).

In the present range of particle sizes the tip folding plays a great role. With the help of a "blind reconstruction method" it is possible to approximate the shape of the tip [1]. After a respective deconvolution of the STM images facetted particles become visible. According to their equilibrium shape - being a truncated octahedron in the case of fcc cobalt - hexagonal and quadrangular facets appear in the images [2]. STS is sensitive to occupied and unoccupied states near the Fermi level and reveals the existence of distinct states in the tunnelling conductivity of the substrate as well as on the clusters. Thus, the richly structured density of states of the germanium surface serves as STM/STS condition test [3]. The tunnelling conductivity measured on the cobalt nanoparticles Ge(001) will be discussed in detail.

[1] J.S. Villarrubia, J. Vac. Sci. Technol. B 14, 1518 (1996), [2] M. Jamet, Phys. Rev. Lett. 86, 4676 (2001), [3] K.-L. Jonas, Appl. Phys. A 82, 131-137 (2006)