Thermally Activated D₂ Emission upon Decomposition of Thin Deuterofullerene Films on Au(111)

We have studied the formation and thermal properties of thin, deuterofullerene-containing films on Au(111) under ultrahigh vacuum conditions. The films were prepared in situ by exposure of predeposited C₆₀ layers to a flux of atomic deuterium. With increasing deuterium dose, a D + C₆₀ → C₆₀D_<i>x</i> reaction front propagates through the fullerene film toward the gold surface. Heating the resulting deuterofullerene-containing films to >600 K leads to desorption of predominantly C₆₀ and C₆₀D_<i>x</i>. Interestingly, some D₂ is also evolved while a significant fraction of the carbon initially deposited is left on the surface as nondesorbable residue. This is in contrast to analogous deuterofullerene-containing films prepared on graphite, which sublime completely but do not measurably evolve D₂, suggesting that the gold surface can act as a catalyst for D₂ formation. To explore this further, we have systematically studied (i) the thermal properties of C₆₀/Au­(111) reference films, (ii) the reaction of C₆₀/Au­(111) films with D atoms, and (iii) the heating-induced degradation of deuterofullerene-containing films on Au(111). In particular, we have recorded temperature-resolved mass spectra of the desorbing species (sublimation maps) as well as performed ultraviolet photoionization spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning tunneling microscopy measurements of the surfaces at various stages of study. We infer that heating deuterofullerene-containing films generates mobile deuterium atoms which can recombine to form molecular deuterium either at the gold surface or on fullerene oligomers in direct contact with it

Thermal Decomposition of the Fullerene Precursor C₆₀H₂₁F₉ Deposited on Graphite

Specially fluorinated polycyclic aromatic hydrocarbons (F-PAHs) are of interest as precursors for transition metal catalyzed CVD growth of chiral-index pure single-walled carbon nanotubes as well as for the rational synthesis of fullerenes. Laser desorption/ionization of a prototypical F-PAH has recently been shown to lead to C₆₀ via a sequence of regioselective intramolecular cyclodehydrofluorination steps: C₆₀H₂₁F₉ → C₆₀H₂₀F₈ + HF → C₆₀H₁₉F₇ + HF ... → C₆₀ (Kabdulov et al. <i>Chem.–Eur. J.</i> <b>2013</b>, <i>19</i>, 17262). We have studied the thermal stability of solid C₆₀H₂₁F₉ films on graphite under UHV conditions toward exploring the extent to which such intramolecular dehydrofluorination can also occur on a hot chemically inert surface and to what extent intermolecular interactions influence such transformation processes. C₆₀H₂₁F₉ films were probed in situ by ultraviolet photoionization, X-ray ionization, Raman spectroscopy, and thermal desorption mass spectrometry, as well as by ex situ atomic force microscopy. Heating multilayer films results first in C₆₀H₂₁F₉ emission from the bulk (peaked at ∼630 K) followed at higher temperatures by desorption from the interface region (in the range 750–850 K). Sublimation from the interface region is also associated with some on-surface cyclo-dehydrofluorination as indicated by C₆₀H_{21–<i>n</i>}F_9–<i>n</i>, <i>n</i> = 1, 2, 3 emission. C₆₀ was not observed in the desorbed material suggesting that complete cage closure cannot be achieved on HOPG. Furthermore, C₆₀H₂₁F₉ deposits cannot be fully removed from HOPG. Instead, competing on-surface polycondensation of reactive intermediates yields a fluorinated carbon phase, which remains stable up to at least ∼1000 K. To complement these studies we have also used mass selective ion beam soft-landing to probe the desorption properties of monodispersed films consisting of mass-selected C₆₀H_{21–<i>n</i>}F_9–<i>n</i> fragments, <i>n</i> = 1, 2