TiO₂ surfaces

Dr. E. Backus

Metaloxide surfaces have lately received a lot of attention owing to their relevance for e.g. catalysis, water splitting, and solar cells. In Mainz we study water on TiO2 surfaces with time-resolved techniques. In this way we can learn about the reorientation dynamics of water on the surface, which provides information about the binding of water to the oxide. Subsequently we will try to split water with a laser pulse and look at the reaction products and the dynamics of the reaction. Moreover, we can adsorb dye molecules on the surface, excite them and study the subsequent electron dynamics.

In this project we will use the technique time-resolved sum-frequency generation spectroscopy. This technique is forbidden in centrosymmetric media and therefore very suitable to study interfaces. For the reorientation dynamics we label a particular vibration by an infrared pump pulse. At a certain time afterwards we probe the vibrations at the surface by exciting with a weak infrared beam and this excitation is subsequently upconverted with a visible beam. The sum-frequency emission gives us then the infrared spectrum. Changing the time between the pump and the probe pulses will give dynamical information.
Water splitting can be initiated by a visible pump pulse. Subsequently we probe the reaction with an infrared and visible probe pulse to generate the sum-frequency light. Also the dye molecules will be studied with this scheme.

Ellen H. G. Backus, Andreas Eichler, Aart W. Kleyn, Mischa Bonn, Science 310 (2005) 1790

Cho-Shuen Hsieh, R. Kramer Campen, Ana Celia Vila Verde, Peter Bolhuis, Han-Kwang Nienhuys, and Mischa Bonn, Phys. Rev. Lett. 107 (2011) 116102