State resolved transient charge transfer in rutile TiO2: applications of light sources in Artemis, Central Laser Facility

In the Artemis facility of Central Laser Facility, time-resolved pump-probe photoemission spectroscopy has been used to study the dynamics of charge carrier recombination and trapping on hydroxylated rutile TiO2(110). By choosing proper pump energies to enable excitations of the defect states and the valence band respectively, we study different recombination processes in TiO2. We observed a very fast retrap of electrons into the polaronic defect states within 45±10 fs after excitation of IR pump pulses. Under the UV excitation that enables band gap transitions, a long lifetime component beyond 1 ps can be identified from the decay of hot electrons at the bottom of the conduction band and the refilling of the band gap states, which points to a band gap state mediated recombination process.We are presently in the process of upgrading our beamline to include a 100-kHz laser system with HHG. With a high repetition rate, we expect to reduce the space charge effect. The data collection efficiency will be significantly enhanced. In the second part of the talk, I will present designs of the new laboratory, experimental capabilities and specifications of the laser systems and beam lines.