Surface Structure and Dynamics by Helium Atom Scattering
Anton Tamtögl
Institute of Experimental Physics, Graz University of Technology
16:00 - 17:00 Tuesday 08 June 2010 TU Graz, Seminarraum PH011150

Helium atom scattering (HAS) provides a gentle and uniquely sensitive probe of surface structure and dynamics. Using helium atoms to probe a surface is truly non-destructive to the sample and a completely inert investigation method. After having set up a new helium atom scattering apparatus and carrying out calibration measurements on LiF(001) our first measurements are concentrated on Bi(111).

Bismuth has attracted renewed interest only recently due to its vast differences between surface and bulk properties. Thus it was shown that the Bi(111) surface is a much better metal than the bulk due to the presence of metallic surface states. Oscillations of the Nernst coefficient in bismuth have been reported and its strong spin-orbit interaction is a promising property of Bi surfaces and interfaces with respect to applications in spintronics.

As opposed to the electronic structure nothing is known about the surface phonons on Bi(111) so far. Thereby HAS experiments are of particular interest on Bi surfaces since the phonon energies are too low to be accessible for other scattering techniques such as electron scattering. We have used elastic and inelastic scattering of helium atoms to study the Bi(111) surface which allows us to give the first report on phonon creation and annihilation events on this surface. Elastic HAS experiments reveal large diffraction peaks corresponding to a large surface charge density corrugation. This is surprising since the reported metallic character of the Bi(111) surface would imply a nearly flat corrugation. The observed surface corrugation and the phonon dispersion may both point to the important role of the strong covalent bonds at the surface.