Lateral Conduction Model for Intermolecular Interaction of Self-Assembled Monolayers

We investigated binary-component self-assembled monolayers (SAMs) and fabricated small domains of a conjugated molecule in preassembled n -alkanethiol SAM films using an implantation technique. We measured the height of the domains by scanning tunneling microscopy and found that, when the size is smaller than ∼5 nm, the observed height of the conjugated molecular domains depends on their lateral size. This size dependence of the domain height indicates that the vertical conductance of the domains should depend on the domain size (number of molecules). When many molecules are interacting, the molecular orbitals are affected, which should cause changes in the electron tunneling and conductance. The degree of the intermolecular interaction was estimated by introducing an effective conductance between the molecules using a classical model similar to a resistor network.