AVS 52nd International Symposium
    Applied Surface Science Thursday Sessions
       Session AS+TF-ThA

Paper AS+TF-ThA1
C@sub n@ (50@<=@n<60) Films on HOPG

Thursday, November 3, 2005, 2:00 pm, Room 206

Session: Thin Film Characterization II
Presenter: A. Böttcher, Universität Karlsruhe, Germany
Authors: A. Böttcher, Universität Karlsruhe, Germany
P. Weis, Universität Karlsruhe, Germany
S.-S. Jester, Universität Karlsruhe, Germany
D. Löffler, Universität Karlsruhe, Germany
M.M. Kappes, Universität Karlsruhe, Germany
Correspondent: Click to Email
Novel solid materials have been grown under ultra high vacuum conditions by gentle deposition of C@sub n@@super +@ (50@<=@n<60) on HOPG surfaces (kinetic energy typically < 0.1 eV/atom). C@sub n@@super +@ ions resulting from the electron-impact induced ionization/dissociation of C@sub 60@ are driven by a system of electrostatic lenses through a mass spectrometer towards the HOPG substrate where an appropriate retarding potential assures their soft-landing. This setup enables to achieve deposition rates in the range of 10@super 12@ ion/s. AFM images reveal that the C@sub n@ films grow according to the Volmer-Weber scenario, i.e. the surface is initially dominated by 2D fractal islands, which in later deposition stages become 3D dendritic pyramids. This behavior stems from the aggregation of C@sub n@ cages, which is driven by reactive sites as formed by adjacent pentagons (or heptagons) on individual cages. The resulting covalent bonds are responsible for the unusually high thermal stability of the C@sub n@ films. Thermal desorption spectra of C@sub 58@ reveal activation energies around 2.2 eV, which are considerably higher than the sublimation enthalpy of C@sub 60@ films. AFM images taken after completing the desorption exhibit a network of highly polymerized cages, which remains stable even at temperatures around 1300 K. Recent DFT calculations as well as UPS-measurements support the aggregation scenario of C@sub n@ cages. Well recognizable features in the valence-band spectra allow identification of the band gap as well as contributions from C@sub n@-C@sub n@ bonds.