Berlin 2008 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 12: Thin Film Characterisation: Structure Analyse and Composition (XRD, TEM, XPS, SIMS, RBS, ...)

DS 12.7: Vortrag

Dienstag, 26. Februar 2008, 13:15–13:30, H 2013

Thermal Stability of Cs Fullerides — •Daniel Löffler, Patrick Weis, Sharali Malik, Artur Böttcher, and Manfred Kappes — Institut für Physikalische Chemie, Universität Karlsruhe, 76131 Karlsruhe, Germany

Thermal stability of solid Cs fullerides fabricated under ultra high vacuum conditions has been investigated by means of thermal desorption spectroscopy, ultraviolet photoelectron spectroscopy and secondary electron microscopy. The incorporation of Cs atoms proceeds by the formation of Cs_xC₆₀ grains. The stability of Cs_xC₆₀ depends on the doping degree x, 1≤x≤6. Weakly doped phases, Cs_x<4C₆₀, decompose in three channels manifested by C₆₀ sublimation peaks, α at 570 K, β at 660-720 K and γ at 820-900 K. Channel α reveals the sublimation of C₆₀ molecules from sample regions not involved in the formation of fulleride grains. Sublimation channel β represents thermal desorption of C₆₀ molecules terminating Cs_xC₆₀ grains, x=1-3. The latter result from the phase segregation nC₆₀^m− ←→ C₆₀ + mC₆₀ⁿ⁻, m=2,3, n=m+1 as activated during heating the sample [1]. The binding energy of C₆₀ cages to the grain surface has been found to vary slightly with x in the range from 1.75 eV up to 1.95 eV. Saturated Cs_xC₆₀, 4≤x≤6, phases decompose only via channel γ by sublimation of Cs_xC₆₀ cages.

[1] G. Klupp et al., Phys. Rev. B, 74 (2006) 195402