Berlin 2015 – scientific programme

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O: Fachverband Oberflächenphysik

O 43: Inorganic/Organic Interfaces: Electronic Properties I

O 43.3: Talk

Wednesday, March 18, 2015, 11:15–11:30, MA 005

Orbital tomography: beyond the plane wave final state approximation — •Peter Puschnig — University of Graz, Institute of Physics, Austria

In recent years it has been shown that the angle-resolved photoelectron cross section from organic molecular films can be accounted for by approximating the final state of the photoemission process by a plane wave. This simple approach, sometimes termed ''orbital tomography'', has led to a number of interesting applications for organic molecules adsorbed on metal surfaces, such as the unambiguous identification of molecular orbitals [1], the determination of molecular orientations [2], or even the reconstruction of real space molecular orbitals [3]. However, this technique has also been criticized since it relies on a crude approximation for the final state whose accuracy and range of validity has been questioned by many.

In this contribution, I will present theoretical results ranging from small molecules, such as benzene, up to extended two-dimensional structures, such as graphene. By comparing to available experimental data, I will identify the limitations of the plane wave approximation and discuss approaches to improve upon it. In particular, a simple modification to take into account the free mean path of photoelectrons and a modification of the final state which allows to account for shape resonances and scattering effects will be demonstrated.

[1] Puschnig et al., Phys. Rev. B 84, 235427 (2011)

[2] Puschnig et al., Science 326, 702-706 (2009)

[3] Lüftner et al., Proc. Nat. Acad. Sci. U. S. A. 111, 605-610 (2014).