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Molecular junctions are nanomaterials made of one molecule, or a thin organic layer, sandwiched between two metallic electrodes.[1] These systems are now widely and intensively studied due to a high potential for nanoelectronic applications. If these devices can now be reliably made and characterized, this field of research is facing a clear issue: the modification of the molecular structure offers a poor control over the device characteristics. The basic idea of the design in Molecular Electronics is that the molecular level landscape in the junction will affect the electron transport, offering control over the current/voltage characteristics.[1-3] Driven by chemical intuition, the usual design of molecular junctions relies on electron donating or accepting building blocks. In this presentation, we show and explain that this approach which focuses on the isolated molecule properties provides a very limited or even erroneous picture as the contact of a molecule to two metal electrodes leads to a completely different entity. Using first principle DFT calculations, we demonstrate that the contact of an asymmetric organic layer to metal electrodes comes with the creation of spontaneous and very intense electric fields in the junction.[4] The origin of this field are the permanent dipole moments in the junction. The built-in field completely modifies the energy landscape in the junction. We argue that only a design that takes into account such large contact renormalization effects could finally lead to the control of the electronic structure of molecular junctions and then move the molecular electronics effort in the intelligent design era. [1] Aviram and Ratner, Chemical Physics Letters, “Molecular rectifiers”, 1974 [2] Van Dyck and Ratner, Nano Letters, 10.1021/nl504091v, 2015 [3] Van Dyck and Ratner, J. Phys. Chem. C, 10.1021/acs.jpcc.6b07855, 2017 [4] Van Dyck and Bergren, Accepted in Advanced Electronic Materials, “Large Built-in Fields Control the Electronic Properties of Nanoscale Molecular Devices with Dipolar Structures”, 2018 Figure 1 |
