Quantum-Dot-Based Scanning Probe d-Band Hole Spectroscopy of Plasmonic Nanoparticles

Despite intense research efforts, quantitative energy-resolved measurements on hot carriers generated due to plasmon decay in metal nanoparticles are rare. This concerns in particular excitations below the Fermi level, i.e., holes. Here, we use a metallized scanning probe tip to measure photocurrents from plasmonic gold nanoparticles through a monolayer of colloidal lead sulfide quantum dots. Separating out current contributions from quantum dot excitons and thermionic emission, we achieve quantitative measurements on the hole excitation quantum efficiency in the gold nanoparticles in the 1.9-2.6 eV energy range. Therefore, we combine systematic experimental bias and wavelength variations and a comparison with the case of aluminum with extensive modeling. The detection scheme can be extended to electron currents and other energy ranges by simply using quantum dots with different energy levels.