PhD-student: Energy and charge transfer correlated to morphology in single hybrid nanosystems

Updated: 3 months ago
Deadline: 30 Jun 2021

The Hybrid Nanosystems group is looking for 2 PhD candidates for a project that aims to unravel the structure-property relationship in hybrid metal-semiconductor nanosystems on a level of individual particles. How does the 3D morphology influence the charge and energy transfer between the metal and the semiconductor components? Can we (locally) tune this interaction by external stimuli? Finding answers to these questions will pave the way towards achieving smart functionality and robustness for energy-harvesting and quantum-processing materials of the future.

Metal and semiconductor nanoparticles (NPs) are emerging as key materials for solar energy harvesting, photocatalysis and photonics. The distinct optical properties of metal NPs stem from the collective oscillation of electrons (plasmons) upon incoming electromagnetic radiation. This makes them strongly interact with visible and near-infrared light, resulting in intense local electromagnetic fields in the vicinity of plasmonic metal NPs. Semiconductor NPs such as quantum dots generate bound electron-hole pairs (excitons) upon absorption of light of an energy larger than the band gap. The latter is a function of size, shape and material and can be tuned from the UV to the infrared. The excited electron-hole pairs can either recombine resulting in photoluminescence, be harvested in photovoltaic applications or promote chemical reactions involving reduction-oxidation processes in photocatalysis.

When both NP types are brought in close vicinity, the charge carriers in the coupled system can interact with each other, potentially leading to charge and energy transfer. This exchange can be used to alter absorption and emission of light, and to enhance chemical reaction rates and photovoltaic efficiencies in such coupled systems. In this manner, existing properties can be enhanced and novel properties might emerge as a consequence of the interaction. The interplay between the different components is dictated by the exact morphology of the hybrid nanosystem, an effect that is masked by averaging over many NPs. To overcome this problem, the interaction between semiconductor and metal NPs needs to be studied on a single NP level by correlating structural and optical properties on the same nanosystem.

In this work, you will investigate the energy and charge transfer processes in hybrid nanosystems and measure the interaction between single metal, semiconductor and dielectric NPs. To reach that goal, you will build a single-particle scattering and (time-resolved) luminescence measurement setup. To correlate the optical properties of the NPs to their morphology, you will perform electron microscopy on the same nanoparticles. The challenge will be to determine not only the 2D but also the 3D arrangement of the coupled NPs. To this end, you will make use of electron tomography. The project will also include modifying the surface chemistry of NPs and applying external stimuli to alter the interaction in hybrid nanosystems. The end goal of the project is unravelling the physics of key interactions within the hybrid nanosystems and finding means for precisely controlling them.

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