Andreas Hohenau

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.

Light field distributions on sample surfaces are mapped by detecting the photocurrents locally induced in a monolayer of colloidal perovskite‐capped PbS quantum dots with a conductive scanning force microsope. The signal levels depend on the illuminating light irradiance according to a power law and the spatial resolution is found to be bias‐dependent in the range of 30–100 nm. We image, first, the Airy intensity pattern of a tightly focused laser beam and, second, the light field distribution in a plasmonic nanoparticle array. With isotropic light absorption and the option of tailoring quantum dots for specific charge generation and transport properties, quantum dots can provide a reliable and generic current read‐out scheme for light field imaging, detection, and sensing.

Photoconductive atomic force microscopy quantitatively probes monolayers of PbS/perovskite quantum dots with a contact area of 1–3 dots in stable and reproducible acquisition conditions for I / V curves and photocurrent maps.

We investigated the optoelectronic properties of lead sulphide (PbS) quantum dot films in lithographically tailored gold nanogap electrodes. In particular, we aimed at the correlated measurement of photoconductivity and luminescence as a tool to characterize the charge dynamics from exciton generation to carrier extraction and recombination. Combining these measurements in an optical microscope with laser scanning excitation enabled, as well, the spatially resolved observation of the involved effects.

We investigate the photoconductivity properties of lead sulphide (PbS) quantum dot ensembles in lithographically tailored gold electrodes with smallest gaps of 15 nm. We demonstrate that quantum dots are reliable nanoscale light/current converters and correlate the measured photocurrents to the quantum dot number, the gap voltage and light irradiance. For the latter, we find a photocurrent power law dependence with an exponent of 2/3. Furthermore, we probe the role of plasmonic effects in the gold electrodes and image by scanning photocurrent microscopy the spatial dependence of photocurrent generation.

Nanometric gaps in plasmonic structures can lead to huge optical near elds and, related, to strongly enhanced interaction of molecules and light. Nanocavities formed by sphere-on-lm or cube-on-lm systems were recently established as promising sys- tems eventually reaching the strong coupling regime. However, such structures are limited with respect of being bound to a surface and by having no means of adjusting the resonance wavelength to the requirements of arbitrary analytes, independent of the gap width. We suggest and investigate in this paper silver-gold compound nanocuboid dimers in colloidal solution as potential structures to mitigate both limitations. We ana- lyze the dimers' plasmonic properties by a combination of optical spectroscopy, electron energy loss spectroscopy and numerical simulations, focusing on the longitudinal dimer geometry and the dominant light-coupled plasmon mode. We then calculate optical eld enhancements under light and electron excitation to assess the cuboid dimer's potential in sensing and spectroscopy applications.

We show that the plasmon modes of vertically stacked Ag–SiO2–Ag nanodisks can be understood and classified as hybridized surface and edge modes. We describe their universal dispersion relations and demonstrate that coupling-induced spectral shifts are significantly stronger for surface modes than for edge modes. The experimental data correspond well to numerical simulations. In addition, we estimate optical intensity enhancements of the stacked nanodisks in the range of 1000.