Semiconductor-metal hybrid nanostructures are interesting materials for photocatalysis. Their tunable properties offer a highly controllable platform to design light-induced charge separation, a key to their function in photocatalytic water splitting. Hydrogen evolution quantum yields are influenced by factors as size, shape, material and morphology of the system, additionally the surface coating or the metal domain size play a dominant role.
In this paper we present a study on a well-defined model system of Au-tipped CdS nanorods. We use transient absorption spectroscopy to get insights into the charge carrier dynamics after photoexcitation of the bandgap of CdS nanorods. The study of charge transfer processes combined with the hydrogen evolution efficiency unravels the effects of surface coating and the gold tip size on the photocatalytic efficiency. Differences in efficiency with various surface ligands are primarily ascribed to the effects of surface passivation. Surface trapping of charge carriers is competing with effective charge separation, a prerequisite for photocatalysis, leading to the observed lower hydrogen production quantum yields. Interestingly, non-monotonic hydrogen evolution efficiency with size of the gold tip is observed, resulting in an optimal metal domain size for the most efficient photocatalysis. These results are explained by the sizedependent interplay of the metal domain charging and the relative band-alignments. Taken together our findings are of major importance for the potential application of hybrid nanoparticles as photocatalysts.
Multiple excitations in quantum dots core/shell heterostructures are studied via quasi continuous wave multiexciton
spectroscopy method. For ZnTe/CdSe core/shell quantum dots, a transfer from attractive to repulsive biexciton binding
energy is detected as the shell thickness increases, indicating a transfer from quasi type-I to type-II regimes. For
CdSe/CdS seeded nanorods, a transfer from binding to repulsive behavior is detected for the biexciton, accompanied by
significant reduction in oscillator strength of the triexciton transition as core diameters decreases below 2.8nm,
indicating a transition of the electronic excited states from type-I localization in the core to a quasi type-II delocalization
along the entire rod as the core diameter decreases. However, as rods dimensions are decreased, a transfer from repulsive
to binding biexciton energy occurs, demonstrating a change of the system from a quasi type-II to quasi-type-I behavior.
A new material platform is described that enables inclusion of nanocrystalline quantum dots into a polymer. This technology is compatible with semiconductor processing and may enable integration of active materials into current waveguide technologies. We describe the steps preformed to fabricate a waveguide chip that contains IR-emitting quantum dots. Optical tests demonstrate guiding and preservation of the quantum dots optical properties through the processing steps. Time resolved optical measurements indicate presence of gain in the InAs quantum dot impregnated polymer.