In situ analysis of plasma-induced material modifications on nanoparticles for functional applications

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The goal of the project is to gain fundamental understanding of plasma-induced modifications of small (<<100 nm) nanoparticles (NPs). Their small size can lead to quantum confinement effects (changing electrical and optical properties), their high surface-to-volume ratio makes them ideal cost-effective candidates for catalytic applications, and their plasmon resonance can be utilized in plasmonic sensors. One of the important parameters is the state of their surface (oxidation, passivation, etc.), which influences very strongly their properties. Non-equilibrium plasmas are a known NP generation and treatment method with several unique properties such as narrow size distribution of generated NPs, selective heating, or effective surface modifications through plasma deposition, passivation, or etching. The processes playing a role in the plasma-NP interaction are, however, understood only qualitatively.The project goal will be pursued by applying in situ UV-Vis absorption spectroscopy to analyze the NP surface plasmon resonance and in situ FTIR absorption spectroscopy to analyze NP surface passivation and modification. The NPs will be generated in separate plasma sources mounted behind a shutter on a processing reactor, which will allow us to study the effects of different plasma conditions and plasma chemistries (oxidation, hydrogen passivation, or even deposition) on freshly-prepared NPs with well-defined size and properties. The in situ and additional ex situ characterization techniques will provide understanding of the fundamental plasma-NP interactions and allow fine-tuning of their properties.An important aspect is that we will not use the plasma as a "black box", but we will systematically study how various plasma components (ions, radicals, etc.) influence the induced changes on small metallic (Ag, Al, Ti) or semiconductor (Si) NPs. Careful analysis of plasma properties using a variety of plasma diagnostic techniques (e.g. Langmuir probe (LP), optical emission spectroscopy (OES), mass spectrometry (MS), etc.) is an essential part of this project. The planned research will strongly benefit from the combination of the complementary material expertise and plasma expertise of both PIs.Achieving the goal of this project will allow us to fully exploit the potential of NP plasma treatment in the generation of high-quality NPs. The targeted properties are, for example, excellent optical plasmonic behavior (metallic or TiN NPs for broadband metamaterial absorbers or plasmonic sensors) or excellent photoluminescence yield and short decay time (direct band gap behavior) of silicon NPs with envisaged application in silicon-based light sources or 3rd generation solar cells.