Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 32: Surface or interface magnetism

O 32.5: Vortrag

Mittwoch, 25. März 2009, 11:30–11:45, SCH A315

Single electron capture versus double electron capture by slow He-ions above transition metal surfaces — •Christian Tusche and Jürgen Kirschner — MPI für Mikrostrukturphysik, D-06120 Halle, Germany

We studied the electron-capture by slow Helium ions (kinetic energy ≤ 30eV) scattered at epitaxial films of the transition metals Mn, Fe, and Ni, grown on a W(110) substrate. At a distance of 2-5Å above the surface, metastable He^** is formed by resonant transfer of electrons from the metal to the 2s or 2p shells of the projectile. The decay of He^** proceeds via the emission of a He-KLL Auger electron with an energy of ≈ 34.5eV or 36.0eV for a triplet or singlet term, respectively. In the experiment, either a beam of metastable He^*+ (2s), or doubly charged He⁺⁺ is used. In the former case, only one electron is transferred to the He ion, while He⁺⁺ captures two electrons.

Based on the assumption of two subsequent, but independent one-electron transitions Unipan et al. [1] related the population of singlet and triplet terms simply to the spin-polarization of the surface. In contrast, we observe largely different triplet contributions using He^*+ (2s) and He⁺⁺, that cannot be explained by a two-step process. Instead, we propose the simultaneous capture of two correlated electrons. Moreover, the triplet population, using double-capture, is particularly sensitive to minute modifications of the surface electronic structure, e.g., by adsorption of sub-monolayers of C and O.

[1] M. Unipan, A. Robin, R. Morgenstern and R. Hoekstra: Phys. Rev. Lett. 96, 177601 (2006)