Professor Majed CHERGUI wins an ERC Advanced Grant
Majed CHERGUI: Charge carrier Dynamics in Metal Oxides
Transition metal (TM) oxides (e.g., TiO2, ZnO, NiO) are large gap insulators that have emerged as highly attractive materials over the past two decades for applications in photocatalysis, solar energy conversion, etc. These applications rely on the generation of charge carriers, their evolution and their eventual trapping at defects or via coupling to photons. Despite the huge interest for such materials, the very nature of the elementary electronic excitations (Frenkel, Wannier or charge transfer exciton) is still not established, nor is the way these excitations evolve after being created: excitonic polarons, charged polarons or free charges. Finally, the electron-hole recombination is also not clearly established because of issues related to defects and trapping.
Over the last decade, Professor Chergui’s group achieved a number of breakthroughs on chemical systems and on materials, using element-selective spectroscopies: namely, ultrafast X-ray absorption and emission. His ERC project aims at pushing further these efforts by implementing novel ultrafast core-level spectroscopies: time-resolved resonant inelastic scattering (TR-RIXS) and time-resolved Angle-resolved photoemission spectroscopy (TR-ARPES), which both can probe the electrons and the holes. The former will exploit the unprecedented brilliance of X-ray Free-electron-lasers. The second will use the high harmonic generation (HHG) source of ultrashort extreme UV (10-100 eV) pulses newly developed by Chergui’s group. While both methods will be implemented for the study of single crystals with a controllable degree of doping (Oxygen vacancies), TR-RIXS will also be implemented on nanoparticles and mesoporous films that are commonly used in functional devices. This combination of hitherto unused cutting-edge technologies on metal oxides will deliver a new degree of insight into the dynamics, trapping and decay of charge carriers in these materials.