The unique versatility of the electronic structures of organic molecules can be potentially utilized to engineer single-molecular electronic devices with specific functionalities. Here, we report on how the electronic structures and the transport properties of molecular junctions containing a $\pi$-conjugated terephthalic acid molecule in a scanning tunneling microscopy (STM) configuration can be tuned by modifying their chemical composition at a single-atom level. More specifically, this strategy implies (i) to change the molecular core through a chemical functionalization process and (ii) to modify the chemical nature of the STM-tip-apex atom. In this respect, our first-principles calculations of the electronic structures and the corresponding electron transport reveal that by the insertion and increase of the number of N atoms in the six-membered benzenelike aromatic ring, the electron transmission at the Fermi level increases. However, the calculated electron transmission at the Fermi level does not depend significantly on the specific position of the N atom in the aromatic ring. Nevertheless, when the tip-apex atom is changed from Cu to W, the electron transmission of the molecular junction significantly changes in an energy range above the Fermi level.

• Received 4 June 2013

DOI:https://doi.org/10.1103/PhysRevB.88.125436