  A race is held between ten species of organic gas molecules on a graphene
substrate driven by thermal gradients via molecular dynamics. Fast conduction
of the molecules is observed with selectivity for aromatic compounds. This
selectivity stems from the fact that the planar structure of the aromatic
molecule helps keep a shorter distance to the substrate, which is the key to
the driving force at the gas-solid interface. The drift velocity monotonically
increases with decreasing molecule density, with no ballistic transport
observable even for a single molecule. A non-linear regime is discovered for
the conduction of benzene molecules under large thermal gradients. At low
temperature, molecules formed aggregation and move collectively along specific
path in the graphene substrate.
