Nanoscopic imaging of energy transfer from single plasmonic particles to semiconductor substrates via STEM/EELS

Localized surface plasmon resonances (LSPRs), the collective oscillations of conduction electrons in metallic nanoparticles, can produce intense near-fields at the resonance wavelengths. Plasmonic nanoparticles have been incorporated in the design of photovoltaic (PV) and photocatalytic devices, where they have been shown to enhance solar energy harvesting efficiency. Research has shown that the addition of plasmonic nanoparticles improves the efficiency of solar light harvesting via one or more of the following mechanisms1: (1) LSPR excitation leads to an increase in path length for incoming light via scattering, thereby increasing light absorption by the semiconductors; (2) energy transfer from the decay of an LSPR directly creates an electron-hole pair in the semiconductor, a process known as plasmon-induced resonant energy transfer (PIRET). Its efficiency relies on the overlap between the LSPR emission and the band gap absorption of the semiconductor2; (3) direct electron transfer (DET) from the nanoparticle to a semiconductor, in which an LSPR decays, through Landau damping, into a “hot” electron that may then scatter into the semiconductor if it has sufficient energy to overcome the Schottky barrier formed at the interface3. Mechanism (1) is only effective for photon energies above the band gap, while mechanism (2) and (3) involve photons with energies below or above the band gap, therefore, are of particular interest and importance. However, despite its importance, little is known about how PIRET and DET operate at the nanoscale, particularly at the level of a single nanoparticle.