Electrostatic force microscopy characterization of trioctylphosphine oxide self-assembled monolayers on graphite

We have studied the self-assembling behavior of trioctylphosphine oxide (TOPO) on a highly oriented pyrolytic graphite surface. TOPO forms stripe-like structures in registry with the underlying graphite lattice. Using electrostatic force microscopy, we have also measured the charge, dipole, and dielectric constant of these monolayer films. The crystalline stripe phase has a net positive charge of about 2 x 10(-5) electron charge per TOPO molecule. The surface dipole due to adsorption is extremely small; this result implies that the dipole moment of TOPO is oriented parallel to the surface. Perfect image charges are not formed inside the graphite.