The energy transfer dynamics at gold/NaCl aq (00.5 M) interfaces was investigated using our recently developed surface plasmon resonance transient reflecting grating (SPR-TRG) method. We focused on two exponential decays in the SPR-TRG signals. The two decays correspond to the relaxation of hot electrons and interfacial heat transfer, respectively. The intensity of each decay changes systematically with increases in the concentration of NaCl, i.e., the former becomes smaller and the latter becomes larger. Considering the relation between the intensity and the dynamics, we concluded that there is some interaction between the hot electrons and the adsorbate on the interface and that the following temperature rise in gold after relaxation of the hot electrons becomes large. This conclusion shows that an ultrafast energy transfer processes by hot electrons exists, and that the process is hindered by the adsorbate. Finally, we discuss the ultrafast energy transfer in relation to the hot electrons and adsorbate on a molecular scale.
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