Light–matter interactions that induce charge and energy transfer across interfaces form the foundation for photocatalysis^1,2, energy harvesting³ and photodetection⁴, among other technologies. One of the most common mechanisms associated with these processes relies on carrier injection. However, the exact role of the energy transport associated with this hot-electron injection remains unclear. Plasmon-assisted photocatalytic efficiencies can improve when intermediate insulation layers are used to inhibit the charge transfer^5,6 or when off-resonance excitations are employed⁷, which suggests that additional energy transport and thermal effects could play an explicit role even if the charge transfer is inhibited⁸. This provides an additional interfacial mechanism for the catalytic and plasmonic enhancement at interfaces that moves beyond the traditionally assumed physical charge injection^9,10,11,12. In this work, we report on a series of ultrafast plasmonic measurements that provide a direct measure of electronic distributions, both spatially and temporally, after the optical excitation of a metal/semiconductor heterostructure. We explicitly demonstrate that in cases of strong non-equilibrium, a novel energy transduction mechanism arises at the metal/semiconductor interface. We find that hot electrons in the metal contact transfer their energy to pre-existing free electrons in the semiconductor, without an equivalent spatiotemporal transfer of charge. Further, we demonstrate that this ballistic thermal injection mechanism can be utilized as a unique means to modulate plasmonic interactions. These experimental results are well-supported by both rigorous multilayer optical modelling and first-principle ab initio calculations.

引起界面上电荷和能量转移的光-物质相互作用形成了光催化^1,2，能量收集³和光检测⁴以及其他技术的基础。与这些过程相关的最常见的机制之一依赖于载流子注入。然而，与这种热电子注入有关的能量传输的确切作用仍不清楚。当使用中间绝缘层抑制电荷转移^5,6或使用非共振激发^7时，等离子辅助的光催化效率可以提高，这表明即使电荷转移，附加的能量传输和热效应也可以发挥显著作用被抑制⁸。这为界面上的催化和等离子体增强提供了额外的界面机制，超越了传统上假定的物理电荷注入^9,10,11,12。在这项工作中，我们报告了一系列超快等离激元测量，这些测量在金属/半导体异质结构的光激发之后，提供了空间和时间上电子分布的直接测量。我们明确证明，在强非平衡情况下，金属/半导体界面处会出现一种新型的能量转换机制。我们发现，金属接触中的热电子将其能量转移到半导体中预先存在的自由电子，而没有等效的时空电荷转移。此外，我们证明了这种弹道热注射机制可以用作调节等离激元相互作用的独特手段。这些实验结果得到严格的多层光学建模和第一原理从头算的支持。