A three-axis goniometer in an UHV molecular beam experiment

Dynamics of Gas-Surface Interactions

2013

General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. AbstractMolecular beam experiments with specially prepared beams allow the study of the interaction of very reactive species at surfaces. In the present case the focus is primarily on the interaction of N-atoms with surfaces. In this chapter questions that will be addressed include: -What is the scattering pattern and energy transfer of N-atoms at surfaces? -Can adsorption of N-atoms lead to a passive layer that is not reactive to incident N-atoms? -Conversely, can N-atoms remove N-atoms in an Eley-Rideal or hot atom reaction?-Does the electronic state of the atoms matter? -Can the interaction already be described by state-of-time art theory? The methods used will be introduced with examples of fast Ar scattering from Ag(111). Subsequently, the interaction of N-atoms with Ag(111) and Ru(0001) will be discussed in order to address the questions listed above. Some work with N 2 will also be shown. Keywords IntroductionThe fate of a chemical reaction is often determined by the availability of energy and the reactivity of the species involved. Energy, both translational and internal, can allow the reactants to overcome activation barriers and possible endoergicity of the reaction. The most probable path on the potential energy surface describing the reaction is thus governed by availability of energy. Working with excess translational energy limits reaction yields but allows exploration of the nature of the potential energy surfaces involved. Scattering experiments were built to carry out such studies both in gas-phase collisions and in atom/molecule surface collisions. In this chapter we focus on the latter case for experimental studies involving reactive atoms and molecules and we compare these results to similar studies with inert noble gas atoms for calibration.The importance of surface scattering experiments was already realized in the 1970's [1][2][3][4]. From the early work two regimes are identified and the corresponding terms thermal scattering and structure scattering were coined. In the first case the processes are dominated by an energy constraint and the thermal energy of the surface is an important parameter. In addition, parallel momentum conservation applies. In the second case the dynamics at the surf...

Section: Methodsmentioning

confidence: 99%

Scattering of Hyperthermal Effusive N and N2 Beams at Metal Surfaces

Gleeson

Ueta

Dynamics of Gas-Surface Interactions

2013

“…69 A quadrupole mass spectrometer ͑QMS͒ can be rotated around the sample to detect the particles leaving the surface in the TOF experiment. Combining the movements of the manipulator and the rotatable QMS gives accurate control ͑by computer͒ over the incidence and exit angles of particles in the scattering experiment.…”

Section: Methodsmentioning

confidence: 99%

O2 transient trapping-desorption at the Ag(111) surface

Raukema

Butler

The Journal of Chemical Physics

1997

Molecular beam scattering experiments of O2 from Ag(111) carried out at a surface temperature of 150 K, which is below the desorption temperature for the molecular chemisorption state, show three different scattering paths: physisorption followed by desorption, direct-inelastic scattering and transient trapping-desorption. The transient trapping-desorption process is attributed to transient adsorption of the molecule in a metastable O2δ− state at the surface. The translational desorption energy of the transiently trapped molecules is far above thermal, strongly dependent on the surface temperature and independent of the translational energy and angle of the incident oxygen molecule. A strongly peaked intensity distribution around the surface normal is observed for the desorption. The transient trapping probability shows a sharp increase above a threshold energy and a subsequent decrease with increasing incidence energy. It is accompanied by a strong broadening in the angular direct-inelastically scattered flux distribution. The possible origin of the metastable O2δ− state will be discussed.

“…[34][35][36] It consisted of a cascaded arc plasma source mounted in a threestage differentially pumped beam line connected to a UHV scattering chamber with a base pressure of 2×10 −10 mbar. This chamber contained the sample, supported on a three-axis goniometer, 37 an ion sputter gun, a residual gas analyzer, and a differentially pumped rotatable quadrupole mass spectrometer (QMS). Ar (gas purity 99.999%) plasma was generated in the cascaded arc source.…”

Section: Methodsmentioning

confidence: 99%

The interaction of hyperthermal argon atoms with CO-covered Ru(0001): Scattering and collision-induced desorption

Ueta

Gleeson

The Journal of Chemical Physics

2011

The interaction of hyperthermal argon atoms with CO-covered Ru(0001): Scattering and collision-induced desorption Ueta, H.; Gleeson, M.A.; Kleijn, A.W. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Hyperthermal Ar atoms were scattered under grazing incidence (θ i = 60 • ) from a CO-saturated Ru(0001) surface held at 180 K. Collision-induced desorption involving the ejection of fast CO (∼1 eV) occurs. The angularly resolved in-plane CO desorption distribution has a peak along the surface normal. However, the angular distribution varies with the fractional coverage of the surface. As the total CO coverage decreases, the instantaneous desorption maximum shifts to larger outgoing angles. The results are consistent with a CO desorption process that involves lateral interaction with neighboring molecules. Furthermore, the data indicate that the incident Ar cannot readily penetrate the saturated CO overlayer. Time-of-flight measurements of scattered Ar exhibit two componentsfast and slow. The slow component is most evident when scattering from the fully covered surface. The ratio and origin of these components vary with the CO coverage.