Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 12: Symposium: Size-Selected Clusters at Surfaces I
(Invited Speakers: Karl-Heinz Meiwes-Broer, Heinz Hövel, Thorsten Bernhardt)
O 12.4: Vortrag
Montag, 25. Februar 2008, 15:15–15:30, MA 005
Mass-selected non-IPR fullerenes deposited on HOPG — •Daniel Löffler, Patrick Weis, Artur Böttcher, and Manfred M. Kappes — Institut für Physikalische Chemie, Universität Karlsruhe (TH), Germany
Cn layers, (48≤n≤68), have been created under ultra high vacuum conditions by low-energy deposition of mass-selected Cn+ clusters onto HOPG surfaces [1][2]. Cn+(48≤n≤68) ions originate from the electron-impact induced ionization and fragmentation of C60 and C70. The resulting Cn cages represent non-IPR building blocks (Isolated Pentagon Rule) and exhibit localized reaction centers (e.g. adjacent pentagons, 2AP, heptagonal rings, HP, squares). This property leads to the formation of covalent intercage bonds, -Cn-Cn-, which are responsible for the high thermal stability of the Cn solid films. The activation energy for desorption of Cn is considerably higher than the value found for related IPR cages. The intercage binding energies found for Cn+ (62≤n≤68) are lower than those found for the corresponding Cn+ (50≤n≤58) cages. This fact indicates that the strength of the Cn-Cn bonds results from the interplay between the cage curvature (pyramidal angle) and the mean number of non-IPR reaction centers per cage. The electronic structure of the valence band, as monitored by UPS (21.2eV), varies significantly with the cage size. The surface ionization potential and the width of the HOMO-LUMO gap dependent on the cage size and on the type of non-IPR sites terminating the cage.
[1] Böttcher et al., PCCP, 7 (2005) 2816
[2] D. Löffler et al., J. Chem. Phys. 125 (2006) 224705