Sauerstoffadsorption an freien und deponierten Clustern

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2005
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Gynz-Rekowski, Felix von
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Oxygen Adsorption on free and deposited Clusters
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Abstract
For many catalytic processes the adsorption and activation of oxygen is of major importance. Nano-particles (cluster) essentially differ in there properties from the well-known macroscopic environment. For example: metal cluster can act as semiconductors or even insulators.

In the context of this work the chemisorption of oxygen on metal (Cu, Pd) and semiconductor clustern (Si) is studied. By means of anion photoelectron spectroscopy (PES) it could be shown that oxygen dissociates on small copper cluster anions. However, molecular oxygen forms an activated hyperoxide species on clusters consisting of 6 to 10 copper atoms.

On small (1-3 atoms) palladium cluster anions oxygen adsorbs dissociatively. With increasing cluster size the influence of oxygen bonding on the forming conduction band of the palladium cluster is fading. However, a definite answer on the chemisorption of oxygen on the larger palladium clusters is not possible up to this point.

Stable clusters can be used as building blocks for new cluster materials. An example is the Fullerit, a solid state formed of C60 clusters. In the present work, "magic" Si7-clusters on surfaces were examined, in particularly the suitability of these cluster as components of a new solid body. The clusters are produced in a magnetron sputter gun, separated and soft landed onto different surfaces.

By means of X-ray electron spectroscopy (XPS) first indications are found, which point to the fact that Si7 on surfaces is very stable in relation to chemical reactions and not likely to merge with neighboring clusters. In contrast, deposited silicon clusters with 8 or 9 silicon atoms exhibit a high reactivity towards oxygen. Results which point in the same direction are obtained by Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS). In addition theoretical simulation are carried out.
Summary in another language
Die Aufnahme und Aktivierung von Sauerstoff ist für viele katalytische Prozesse von Bedeutung. Nanopartikel (Cluster) unterscheiden sich in ihren Eigenschaften essentiell von der uns bekannten makroskopischen Umgebung. So zum Beispiel können Cluster aus Metallatomen durchaus halbleitend oder sogar Isolatoren sein. Im Rahmen dieser Arbeit wurde die Chemisorption von Sauerstoff an Metall- (Cu, Pd) und Halbleiterclustern (Si) untersucht.

Mittels Anionen-Photoelektronenspektroskopie (PES) konnte an freien Cluster-Anionen gezeigt werden, dass Sauerstoff an kleine Kupfer-Clusternanionen dissoziiert, wo hingegen molekularer Sauerstoff an Clustern mit 6 bis 10 Kupferatomen aktiviert als Hyperoxid bindet. Ebenso dissoziiert Sauerstoff an kleinen Palladium-Clusternanionen (1-3 Atome). Mit steigender Clustergröße verliert sich der Einfluss des Sauerstoffs auf das entstehende Leitungsband der Palladium-Cluster. Über die Art der Bindung ist jedoch keine endgültige Aussage möglich.

Stabile Cluster können als Bausteine für neue Clustermaterialien verwendet werden. Ein Beispiel ist das Fullerit, ein Festkörper aus C60 Clustern. In der vorliegenden Arbeit wurden die Eigenschaften von "magischen" Si7-Clustern auf Oberflächen untersucht, speziell die Eignung dieses Clusters als Baustein für einen neuen Festkörper. Dazu wurden die Cluster in einer Magnetronsputterquelle erzeugt und durch weiches Landen auf unterschiedlichen Oberflächen abgeschieden.

Mittels der Röntgenphotoemission (XPS) konnten erste Indizien gefunden werden, die darauf hindeuten, dass Si7 auf der Oberfläche sowohl gegenüber chemischen Reaktionen als auch gegenüber Verschmelzen sehr stabil ist. Deponierte Cluster mit 8 beziehungsweise 9 Siliziumatomen zeigen ein davon sehr deutlich abweichendes Verhalten. Indizien, die in die gleiche Richtung weisen, konnten auch mittels Auger-Elektronenspektroskopie (AES) und hochaufgelöster Elektronenenergieverlustspektroskopie (HREELS) gefunden werden. Zur Erhärtung dieser These tragen theoretische Simulationsrechnungen bei.
Subject (DDC)
530 Physics
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Chemisorption,Nanokatalyse,Clustermaterial,chemisorption,nanocatalysis,cluster material
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ISO 690GYNZ-REKOWSKI, Felix von, 2005. Sauerstoffadsorption an freien und deponierten Clustern [Dissertation]. Konstanz: University of Konstanz
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@phdthesis{GynzRekowski2005Sauer-4950,
  year={2005},
  title={Sauerstoffadsorption an freien und deponierten Clustern},
  author={Gynz-Rekowski, Felix von},
  address={Konstanz},
  school={Universität Konstanz}
}
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