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Prof. Aart W. Kleijn
Director, Center of Interface Dynamics for Sustainability,
CDCST, CAEP, Chengdu, China |
Abstract: Almost all chemical reactions at surfaces proceed via the Langmuir-Hinschelwood mechanism. In such a reaction all reactants equilibrate to the surface before meeting by diffusion and reacting. By contrast, Eley-Rideal reactions are prompt reactions occurring on impact of an atom or molecule from the gas phase. In environments where hyperthermal reactive atoms are present such as on spacecraft, such Eley-Rideal type reactions can be expected. However, these have not yet been observed under well-defined conditions for heavy atoms such as nitrogen. Only for hydrogenic reactions Eley-Rideal reactions have been demonstrated under UHV conditions. In this work we present results of a systematic study into the importance of such reactions and report the first observations thereof. In the experiments an effusive beam of hyperthermal (5 eV) nitrogen atoms is aimed at a Ru(0001)-O(2x1) surface at an angle of 60 degrees from the surface normal. Upon N-atom impact hyperthermal (4 eV) NO is detected. The angular distribution is peaked in the forward direction with a peak at 30 degrees from the normal, indicating that part of the N-atom parallel momentum is conserved in the NO forming collision. These are strong signatures of a prompt surface reaction. To check the efficiency of the reaction, the time-of-flight spectra of the NO produced were measured for successive intervals. It became clear that fast NO was no longer produced, even though NO is still present in the back ground. From the decay of the NO production rate as a function of time the reactive cross section for the N+O=> NO reaction could be determined. It is about 2 Å2. Such a high cross section is another evidence for an Eley-Rideal reaction. Prompt reactions can be used to specifically remove adsorbates from surfaces. We will demonstrate that not only O-atoms but also N-atoms can be removed from surfaces. The N+N reaction is particularly efficient.
About the Speaker: Aart W. Kleijn (Kleyn used in Scientific Publications) received his bachelor degree in chemistry and mathematics at Leiden University in 1972, and master degree in physics with mathematics and geochemistry at the University of Amsterdam. He obtained his PhD in Physics at the same University in 1980, cum laude. He worked as Post Doctoral Fellow with IBM Research in 1980-1981. He was a member of the scientific staff of the FOM Institute for Atomic and Molecular Physics (AMOLF) in Amsterdam at several levels from 1981 until 1999. He became Professor of physics at the University of Amsterdam in 1988. In 1999 he joined the faculty of Leiden University as professor of chemistry. In 2003 he was appointed Director of the FOM Institute for Plasma Physics Rijnhuizen in Nieuwegein. In 2010 he joined the University of Amsterdam and was the Director of the van’t Hoff Institute for Molecular Sciences until 2014. In that year he was appointed founding director of the Center of Interface Dynamics for Sustainability in Chengdu, Sichuan, China. His current research interests are plasma-surface interaction and molecular processes at surfaces.
Date&Time: March 26, 2014 (Wednesday), 14:00 -15:00
Location: 606 Conference Room
