Lecture
Van Marum Colloquium: Surface chemistry studies for plasma applications
- Date
- Tuesday 11 June 2024
- Time
- Location
-
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden - Room
- CE.0.18
Abstract
Plasmas contain highly reactive species such as radicals and ions, creating a challenging environment for materials. Plasma-activated species often experience a lower barrier for interactions at surfaces, making them interesting for plasma-enhanced catalytic reactions and for plasma-assisted cleaning of surfaces, for example preventing the buildup of carbon and oxidation during exposure to ionizing radiation and electrons. Understanding the mechanisms that govern the evolution of surfaces exposed to plasmas is, however, demanding. Surfaces in plasma interact with a “zoo” of different reactive species with individual energy distributions, calling for the reduction of complexity and the application of in situ characterization methods. In the Materials and Surface Science group at ARCNL, we connect in situ spectroscopy of surfaces to plasma applications, aiming to understand surface processes driven by the reactive environments of plasma applications.
The surfaces of many catalytically active metals have been widely studied in the past, often in the form of simplified model systems. The oxidation of the Ru(0001) surface is an example, for which, despite decades of study, understanding of the intermediate oxide between the first monolayer of oxygen and bulk-like RuO2 remains elusive. Using in situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), we uncover a two-step oxidation process and its characteristic dependence on oxygen pressure and surface roughness. In collaboration with density functional theory experts, we explain this finding by introducing Ru vacancies to the previously predicted structural model. This modified structural model connects well to striking differences observed in NAP-XPS studies of the interaction of different Ru oxides with silane (SiH4), a common etch product in hydrogen plasmas. A more advanced level of in situ XPS allows for the study of surfaces during exposure to plasma activated species. For the example of Ru surfaces exposed to plasma-activated N2 and N2-H2 mixtures, we show the formation of (hydrogenated) nitrogen-metal bonds at the surface and a temperature-dependent concentration of ammonia and N2Hn species in residual gas analysis.