Dielectric properties of polar-phthalocyanine monolayer systems with repulsive dipole interaction

Changes in the work function (WF) of phthalocyanine-graphite systems were investigated as functions of phthalocyanine coverage and the value of the molecular dipole moment by using ultraviolet photoelectron spectroscopy. The dipoles in the film were found to be perpendicular to the graphite surface, and the coverage dependence of the WF of each dipole-phthalocyanine-graphite system clearly exhibited a sudden increase before the monolayer formation depending on the value of the dipole moment. The results show that the dipole-dipole repulsive interaction impacts the growth and structure of monolayer systems with weak intermolecular and molecule-substrate electronic coupling. The electric dipole moment and polarizability of each phthalocyanine in a monolayer was estimated by analyzing the observed coverage dependence of the WF using the Topping model (nanoscale method). Furthermore, it was demonstrated that the dielectric constant obtained with the nanoscale method and that estimated using the Helmholtz equation (macroscopic method) were almost the same. This agreement substantiates the application of the macroscopic model to an organic monolayer that is not a continuum medium.