Structural study of monolayer cobalt phthalocyanine adsorbed on graphite

TL;DR

This study investigates the microscopic arrangement and ordering of cobalt phthalocyanine molecules on graphite, revealing how coverage affects molecular orientation and chain formation, supported by experimental STM data and theoretical modeling.

Contribution

It provides new insights into the molecular arrangement and phase behavior of cobalt phthalocyanine on graphite, combining high-resolution microscopy with potential energy calculations.

Findings

Single molecules align with substrate lattice directions at low coverage

Molecules form chains at slightly higher coverage

Two distinct monolayer phases identified and modeled

Abstract

We present microscopic investigations on the two-dimensional arrangement of cobalt phthalocyanine molecules on a graphite (HOPG) substrate in the low coverage regime. The initial growth and ordering of molecular layers is revealed in high resolution scanning tunneling microscopy (STM). On low coverages single molecules orient mostly along one of the substrate lattice directions, while they form chains at slightly higher coverage. Structures with two different unit cells can be found from the first monolayer on. A theoretical model based on potential energy calculations is presented, which relates the two phases to the driving ordering forces.