Project

Photoemission; Electron mean free path; Angle-resolved photoemission; X-ray photoelectron diffraction; Electronic structure; Atomic / crystallographic structure; Oxides; Low dimensional systems; Layered materials; Molecules; Minerals

Lead
Lay summary
For the microscopic understanding of new materials, the photoemission experiment is unique in its possibility to probe the energy and momentum distribution of electrons responsible for various unexpected and interesting properties of materials. It also offers to probe the local atomic/crystallographic structure via photoelectron diffraction. However, photoemission is intrinsically surface sensitive due to the limited mean free path of escaping photoelectrons and, in cases, it may be doubtful to "practice" bulk physics based on photoemission results. Therefore, this project is concerned with enhancing the bulk sensitivity of the photoemission experiment in order to probe true bulk or interface properties with respect to the atomic/crystallographic and electronic properties. We intend to concentrate our activities on topics a), b) and c) described below. a) Oxide based materials / heterostructures and multilayers: These are emerging materials with both, very high potential for applications and a desperate need for better understanding the physics behind the rich phenomenology. Photoemission experiments are very promising to significantly increase insight, provided we can render them more bulk sensitive. b) Low dimensional systems, layered compounds: These are materials where we search for a better understanding of phenomena like the formation of charge density waves, superconductivity, quasi-particles and electron correlations, based on models made for the bulk material. However experimental information obtained from photoemission mostly stems from the surface. Again it is desirable to collect the same detailed information relevant for the bulk.c) Further areas of interest, molecules and minerals: Here we search to apply photoemission experiments to materials relevant in a cross disciplinary context. These range from molecular systems where photoemission may determine the valence of an element to minerals where the behavior of particular constituents or ingredients is of strong interest.

Direct link to Lay Summary

Last update: 21.02.2013

Number	Title	Start	Funding scheme

On the 1.1.2009 the group of P. Aebi has been transferred from Neuchâtel (NE) to Fribourg in order to re-group condensed matter research activities of the "Mittelland" in Fribourg and therefore to create critical mass and synergy. Prerequisites are now excellent for common research projects in the field of materials with novel electronic properties. It is the aim of this R’Equip project to "profit" from this transfer to improve and update the existing photoemission experiment stemming from 1988 (ESCA spectrometer, taken from L. Schlapbach, UniFR) and 1994 (Scienta spectrometer, taken from Y. Baer, UniNE).Presently at UniFR, in the group of Ch. Bernhard, sophisticated facilities to produce new materials are available (i.e. pulsed laser deposition) as well as diverse techniques to analyze them. The group of B. Grobety has electron microscopy and X-ray diffraction techniques for detailed characterization. With the condensed matter theory group of D. Baeriswyl, a local collaboration is possible for theoretical understanding of these complex materials. Furthermore, photoemission is also of interest for the chemistry groups of K. Fromm and M. Albrecht (photoemission experiments have already been done in NE for these groups).However, photoemission experiments (which are unique in giving direct access to the energy and momentum distribution of electrons responsible for the electronic properties) are intrinsically surface sensitive due to the limited mean free path of the escaping electrons. Therefore, in order to probe the true bulk properties, the worldwide efforts to render photoemission experiments more bulk sensitive have to be followed. Both, lower and higher photon energies will increase the inelastic mean free path of escaping electrons thereby rendering the experiment more bulk sensitive. With this R’Equip project we intend to implement the necessary extension in both directions because two different types of information are gained, i.e., on the electronic and atomic structure with low- and high-energy photons, respectively. We intend to concentrate our activities on topics a), b) and c) described below. a) Oxide based materials / heterostructures and multilayers: These are emerging materials with both, very high potential for applications and a desperate need for better understanding the physics behind the rich phenomenology. Photoemission experiments are very promising to significantly increase insight, provided we can render them more bulk sensitive. b) Low dimensional systems, layered compounds: These are materials where we search for a better understanding of phenomena like the formation of charge density waves, superconductivity, quasi-particles and electron correlations, based on models made for the bulk material. However experimental information often obtained from photoemission mostly stems from the surface. Again it is desirable to collect the same detailed information relevant for the bulk.c) Further areas of interest, molecules and minerals: Here we search to apply photoemission experiments to materials relevant in a cross disciplinary context. These range from molecular systems where photoemission may determine the valence of an element to minerals where the behavior of particular constituents or ingredients is of strong interest.