Monitoring Charge Transfer Dynamics of Surface Trapped Holes in ZnO Surface Utilized for Ethanol Oxidation Using Heterodyne Transient Grating Spectroscopic Techniques

We observed the responses of the ZnO thin film by the near-field heterodyne transient grating (NF-HD-TG) technique to investigate the photoexcited charge carrier dynamics taking place at the ZnO/ethanol interface. We successfully assigned the observed components to the recombination of the surface trapped electrons and the charge transfer of the surface trapped holes utilized for ethanol oxidation, respectively. In addition, by employing the charge carrier-selective heterodyne transient grating (CS-HD-TG) technique, we successfully determined the energetic position of the hole trap state existing in the ZnO surface, responsible for the charge transfer.