We extend our previous development of electron transport through one-dimensional (1D) molecular junctions to two-dimensional (2D) monolayers. Our methodology calculates the tunneling current through a single molecule that is embedded in an infinite 2D monolayer of such molecules self-assembled on gold and covered on top also with gold. In this way, the intermolecular interactions that take place between neighboring molecules are fully accounted for within the accuracy of the density-functional theory. As application examples, we study monolayers of nitro substituted oligo phenylene-ethynylene (nitroOPE) dithiol molecules. Monolayers with the packing density observed experimentally are compared against others with lower density, in which the intermolecular interactions are negligible. Additionally, two different adsorption sites (hollow and atop) are considered for the nitroOPE. The results show that the effect of the intermolecular interactions on the tunneling current depends heavily on the adsorption site of the molecule. Hollow-site-adsorbed monolayers undergo a dramatic reduction in current due to the intermolecular interactions, whereas the change in atop-site-adsorbed monolayers is minimal.

• Received 27 May 2008

DOI:https://doi.org/10.1103/PhysRevB.78.155421