Circular Dichroism in Photoemission from Non-Magnetic Materials

Abstract

Circular dichroism in the angular distribution (CDAD) of photoelectrons is a unique feature appearing if the emission is excited by circularly polarised Synchrotron Radiation. It was first predicted to appear in emission from oriented molecules. Therefore, first experiments on adsorbed molecules have been done in restricted geometries. Later it was found in experiments that the solid surface itself implies the break of symmetry that is needed to observe CDAD in emission from non-magnetic materials. The CDAD in emission from adsorbates or surfaces is a direct consequence of photoelectron diffraction. The distribution of the CDAD in the hemisphere above the sample can be interpreted as hologram. It will be shown how this type of dichroic hologram can be used to reconstruct the real space distribution of the atoms in a solid, or in an adsorbate - substrate system. Different elements can be identified in compounds or alloys due to the elemental sensitivity of X-ray photoemission. As further application it will be shown how CDAD can be used in photoemission microscopy as a contrast giving mechanism.