Electronic Structure Rearrangements as a Source of Negative Differential Resistance in Molecules
Y Simon-Manso, Carlos A. Gonzalez, V Mujica, Y Aray, M Ratner
A qualitative explanation for the experimentally observed negative differential resistance (NDR) in current-voltage characteristics of molecule-metal tunneling junctions is provided. The model is based in DFT calculations of the electronic structure of bridge molecules in a capacitor-like electric field that mimics the potential spatial profile of the junction. Our results show that a plausible mechanism for NDR behavior in planar molecular bridges, like the prototype molecule p-conjugated phenyl-ethylene oligomer 2 -amino-4,4 -di(ethynylphenyl)-5 -nitro-1-benzenethiolate, involves a substantial rearrangement of the charge density of the neutral bridge at a threshold voltage. This change in the polarization pattern of the molecule translates into an energy shift that makes a delocalized molecular orbital coincide with the Fermi energy of the metal contact. This event creates a conduction channel at the Fermi energy. A subsequent voltage increase causes an inversion of the molecular dipole moment and the closing of the conduction channel due to a misalignment with the metal Fermi level . Our results contradict previous explanations based on a reduction mechanism of the molecular bridge and stress the importance of both field and geometry optimization in the study of electrified interfaces. Furthermore, our calculations give a consistent interpretation of the relevant experimental information without invoking significant geometric changes, an unlikely event given the energetic barriers involved compared to the thermal energy.
Journal of the American Chemical Society
Charge Density Rearrangement, Density Functional Theory, Molecular Electronics, Negative Differential Resistance
, Gonzalez, C.
, Mujica, V.
, Aray, Y.
and Ratner, M.
Electronic Structure Rearrangements as a Source of Negative Differential Resistance in Molecules, Journal of the American Chemical Society
(Accessed September 30, 2023)