Mechanisms of plasmon induced charge separation and recombination at gold nanoparticle supported on different size TiO_2 film systems

摘要

Study of plasmon-induced charge transfer mechanism in gold-TiO_2 system is crucial and promising in the solar cell application. To investigate charge separation and recombination dynamics in gold/TiO2 nanoparticle systems, we used ultrafast visible-pump/IR-probe femtosecond transient absorption spectroscopy method. In our experimental study, anatase TiO_2 with different particle size 9 nm and 20 nm were chosen as electron acceptors. Plasmon-induced electron transfer from the gold nanoparticle to the conduction band of TiO_2 was studied by optical excitation of the surface plasmon band of gold nanoparticle at 550 nm. The transient absorption kinetics were studied by probing at 3440 nm to observe intraband free electron adsorption in TiO_2. In our experimental results, electron injection was found to be completed within the apparatus time resolution (240 fs), the charge recombination decay within 1.5 ns was nonexponential. And when laser power changed from 0.5 μJ to 1.9 μJ, the recombination decay didn't depend on the excitation intensity. It is interesting that we found the measured back electron transfer kinetics up to 1.5 ns were strongly dependent on the particle size of TiO_2. The plasmon-induced charge transfer mechanisms will be discussed.