Carbon and ice make
up a substantial proportion of our Universe. Recent space exploration has shown
that these two chemical species often coexist including on comets, asteroids
and in the interstellar medium. Here we prepare mixtures of C<sub>60</sub> fullerene
and H<sub>2</sub>O by vapor co-deposition at 90 K with molar C<sub>60</sub>:H<sub>2</sub>O
ratios ranging from 1:1254 to 1:5. The C<sub>60</sub> percolation threshold is
found between the 1:132 and 1:48 samples, corresponding to a transition from
matrix-isolated C<sub>60</sub> molecules to percolating C<sub>60</sub> domains
that confine the H<sub>2</sub>O. Below this threshold, the crystallization and
thermal desorption properties of H<sub>2</sub>O are not significantly affected
by the C<sub>60</sub>, whereas the crystallization temperature of H<sub>2</sub>O
is shifted towards higher temperatures for the C<sub>60</sub>-rich samples.
These C<sub>60</sub>-rich samples also display exotherms corresponding to the
crystallization of C<sub>60</sub> as the two components undergo phase
separation. More than 60 volume percent C<sub>60</sub> is required to significantly
affect the desorption properties of H<sub>2</sub>O. A thick blanket of C<sub>60</sub>
on top of pure amorphous ice is found to display large cracks due to water
desorption. These findings may help understand the recently observed unusual surface
features and the H<sub>2</sub>O weather cycle on the 67P/Churyumov–Gerasimenko
comet.
Amorphous Mixtures of Ice and C60 Fullerene