Thermally
Activated D<sub>2</sub> Emission upon Decomposition
of Thin Deuterofullerene Films on Au(111)
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Abstract
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 C<sub>60</sub> layers
to a flux of atomic deuterium. With increasing deuterium dose, a D
+ C<sub>60</sub> → C<sub>60</sub>D<sub><i>x</i></sub> 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 C<sub>60</sub> and
C<sub>60</sub>D<sub><i>x</i></sub>. Interestingly, some
D<sub>2</sub> 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 D<sub>2</sub>, suggesting that the gold surface can act as
a catalyst for D<sub>2</sub> formation. To explore this further, we
have systematically studied (i) the thermal properties of C<sub>60</sub>/Au(111) reference films, (ii) the reaction of C<sub>60</sub>/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