  Despite the common expectation that conjugated organic molecules on metals
tend to adsorb in a flat-lying wetting layer, several recent studies have found
strong indications for coverage-dependent transitions to upright-standing
phases, which exhibit notably different physical properties. In this work, we
argue that from an energetic perspective, thermodynamically stable
upright-standing phases may be more common than hitherto thought. However, for
kinetic reasons this phase may often not be observed experimentally. Indeed,
using first principles kinetic Monte Carlo simulations, we find that the
structure with lower molecular density is (almost) always formed first,
reminiscent of Ostwalds rule of stages. The phase transitions to the
thermodynamically stable upright-standing phase are likely to be kinetically
hindered under conditions typically used in surface science (gas phase
adsorption at low flux). This provides a possible explanation why they are
commonly not observed. Investigating both the role of the growth conditions and
the energetics of the interface, we find that the time for the phase transition
is determined mostly by the deposition rate and, thus, mostly independent of
the nature of the molecule.
