Integrating plasmonic nanoparticles with semiconductor substrates introduces strong optical resonances that extend and enhance the spectrum of photocatalytic and photovoltaic activity. The effect of plasmonic resonances has been variously attributed to the field nanoconfinement, plasmon–exciton coupling, hot electron transfer, and so on, based on action spectra of enhanced photoactivity. It remains unclear, however, whether energized carriers in the substrate are generated by the transfer of plasmonically generated hot electrons from the metal, as broadly believed, or directly by dephasing of the plasmonic field at the interface. Here, we demonstrate the importance of the direct plasmonic coupling across the chemical interface for hot electron generation at a prototypical Ag nanocluster/TiO₂ heterojunction by direct probing of the coherence and hot electron dynamics with two-photon photoemission spectroscopy. Energy, time and material distributions of excitations in the Ag nanocluster/TiO₂ heterojunction indicate that dielectric coupling with the substrate renormalizes the plasmon resonance of the Ag nanoparticle, and its dephasing directly generates hot electrons in TiO₂ on a <10 fs timescale.

将等离激元纳米颗粒与半导体衬底结合在一起会产生强大的光学共振，从而扩展并增强光催化和光伏活性的光谱。基于增强的光活性的作用谱，等离子体共振的影响被不同地归因于场纳米限制，等离子体激子耦合，热电子转移等。然而，尚不清楚衬底中受激的载流子是由金属产生的等离激元产生的热电子转移产生的，还是如人们普遍认为的那样，还是直接由界面处的等离激元场的移相产生的。在这里，我们证明了在典型的Ag纳米团簇/ TiO ₂上通过化学界面进行直接等离激元耦合对于产生热电子的重要性通过使用双光子光发射光谱直接探测相干性和热电子动力学来实现异质结。Ag纳米团簇/ TiO ₂异质结中激发的能量，时间和材料分布表明，与基板的介电耦合使Ag纳米粒子的等离子体激元重新规范化，并且其相移在<10 fs的时间尺度上直接在TiO _2中产生热电子。