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Hydrogen-induced mitigation of O on Ru(1010): a density-functional study
1Institute of Physics of National Academy of Sciences of Ukraine, Prospect Nauki 46, Kiev 03028, Ukraine. yakov@iop.kiev.ua
Physical Chemistry Chemical Physics : PCCP
|October 22, 2009
Summary
Atomic hydrogen spontaneously hydrogenates adsorbed oxygen on ruthenium surfaces, forming hydroxyl radicals. Heating to 320-330 K in molecular hydrogen efficiently removes oxygen, crucial for EUV optics.
Area of Science:
- Surface Science and Catalysis
- Materials Science for Extreme Ultraviolet (EUV) Optics
Background:
- Understanding the interaction of hydrogen and oxygen on ruthenium surfaces is critical for applications like extreme ultraviolet (EUV) lithography.
- Previous studies indicate challenges in completely removing oxygen from ruthenium capping layers on Si/Mo mirrors.
Purpose of the Study:
- To investigate the reaction pathways of hydrogen with adsorbed oxygen on a Ru(1010) surface.
- To elucidate the mechanisms hindering complete oxygen removal from ruthenium layers used in EUV optics.
Main Methods:
- Density-functional calculations were employed to model the reaction energetics and mechanisms.
- Kinetic Monte Carlo simulations were used to simulate the surface reactions over time.
- Comparison with experimental data was performed to validate the simulation results.
Main Results:
- Molecular hydrogen does not react with adsorbed oxygen; only atomic hydrogen is reactive.
- Atomic hydrogen reacts with adsorbed oxygen to form hydroxyl (OH) molecules.
- Subsequent reactions can lead to water formation and desorption, or hydrogen molecule (H2) formation and desorption, with H2 formation hindering complete oxygen removal at 300 K.
- The calculated activation barrier for H + OH reaction (0.92 eV) and water desorption temperature (~320 K) align with experimental observations.
- A higher temperature H2 desorption peak (~350 K) indicates that between 320-330 K, H atoms preferentially react with OH.
Conclusions:
- Simulations predict that heating the ruthenium surface to 320-330 K in a molecular hydrogen atmosphere is an effective method for removing chemisorbed oxygen.
- This finding offers a potential solution for improving the stability and performance of Ru capping layers in EUV optics.
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