AVS 60th International Symposium and Exhibition
    Surface Science Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA12
NO Formation in Eley-Rideal Reactions with Hyperthermal N Atoms

Thursday, October 31, 2013, 5:40 pm, Room 202 A

Session: Surface Dynamics and Non-adiabatic Processes
Presenter: A.W. Kleyn, University of Amsterdam, Netherlands
Authors: T. Zaharia, Materials innovation institute (M2i), Netherlands
A.W. Kleyn, University of Amsterdam, Netherlands
M.A. Gleeson, FOM Institute DIFFER, Netherlands
Correspondent: Click to Email
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 nitrogen atoms is aimed at a Ru(0001)-O(2x1) surface at an angle of 60 degrees from the surface normal. Measurements of the angular distribution for Argon scattering under the same conditions have revealed that this surface is atomically flat and uncorrugated. 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.