Marcus Knapp

Heterogeneous oxidation catalysis on ruthenium: bridging the pressure and materials gaps and beyond

It is shown that both the materials and the pressure gaps can be bridged for ruthenium in heterogeneous oxidation catalysis using the oxidation of carbon monoxide as a model reaction. Polycrystalline catalysts, such as supported Ru catalysts and micrometer-sized Ru powder, were compared to single-crystalline ultrathin RuO2 films serving as model catalysts. The microscopic reaction steps on RuO2 were identified by a combined experimental and theoretical approach applying density functional theory. Steady-state CO oxidation and transient kinetic experiments such as temperature-programmed desorption were performed with polycrystalline catalysts and single-crystal surfaces and analyzed on the basis of a microkinetic model. Infrared spectroscopy turned out to be a valuable tool allowing us to identify adsorption sites and adsorbed species under reaction conditions both for practical catalysts and for the model catalyst over a wide temperature and pressure range. The close interplay of the experimental and theoretical surface science approach with the kinetic and spectroscopic research on catalysts applied in plug–flow reactors provides a synergistic strategy for improving the performance of Ru-based catalysts. The most active and stable state was identified with an ultrathin RuO2 shell coating a metallic Ru core. The microscopic processes causing the structural deactivation of Ru-based catalysts while oxidizing CO have been identified.

Long-term stability of Ru-based protection layers in extreme ultraviolet lithography: A surface science approach

Extreme ultraviolet lithography (EUVL) is a leading candidate for next-generation lithography for the semiconductor industry. This technology uses EUV light with a wavelength of 13.5nm (92.5eV) to be able to produce features as small as 20nm in size. The short wavelength of EUV means that reflective optics is needed for lithography in the form of Si–Mo multilayer stacks. However, surface contamination by water and hydrocarbons together with EUV light reduces unacceptably the mirror reflectivity with time. In this article, the authors review the material properties of two promising capping layer materials, Ru and RuO2, for protecting the EUVL mirrors against oxidation, carbon uptake, and the permeation of hydrogen and oxygen. Special emphasis is put on the surface properties of these potential cap layer systems. For both materials the microstructure, the morphology, and the stability under oxidizing and reducing environments are reviewed to promote the search for a successful candidate for a capping layer ...

Dynamic response of chlorine atoms on a RuO2(110) model catalyst surface

The dynamic behavior of surface accommodated chlorine atoms on RuO(2)(110) was studied by a variety of experimental methods including high resolution core level shift, thermal desorption-, and in situ infrared spectroscopy as well as in situ surface X-ray diffraction in combination with state-of-the-art density functional theory calculations. On the chlorinated RuO(2)(110) surface the undercoordinated oxygen atoms have been selectively replaced by chlorine. These strongly bound surface chlorine atoms shift from bridging to on-top sites when the sample is annealed in oxygen, while the reverse shift of Cl from on-top into bridge positions is observed during CO exposure; the vacant bridge position is then occupied by either chlorine or CO. For the CO oxidation reaction over chlorinated RuO(2)(110), the reactant induced site switching of chlorine causes a site-blocking of the catalytically active one-fold coordinatively unsaturated (1f-cus) Ru sites. This site blocking reduces the number of active sites and, even more important, on-top Cl blocks the free migration of the adsorbed reactants along the one-dimensional 1f-cus Ru rows, thus leading to a loss of catalytic activity.