Towards a better characterization of molecular transistors
March 5, 2018
An international team of researchers proposes a new method that uses magnetic fields to distinguish between molecular junctions with and without electronic interactions.
Molecular junctions are nanoscale electronic devices consisting of two metallic electrodes and a molecule sandwiched between them. The molecule acts as a bridge for the electrical charges that flow between the electrodes. These systems have applications in the design of more efficient electronic devices, as their small size would imply a greater number of integrated components as compared with conventional transistors. However, the electronic transport mechanism in molecular junctions must first be well understood. This study has proposed and verified a method that determines whether conduction electrons suffer strong repulsive interactions within the molecule.
One of the peculiarities of molecular junctions are the quantum phenomena that appear due to their small size. One of the most prominent quantum effects is the discretization of energy levels within the molecule. When the molecule couples to metal contacts, the separation between energy levels changes strongly in relation to the situation where the molecule is free. On the other hand, electrons feel the Coulomb repulsion inside the molecule. This repulsion can be screened by the attached contacts. Therefore, it is essential to find out whether or not a molecular junction is subject to electronic interactions, since they ultimately determine the electrical properties measured in the laboratory.
A research work involving scientists from USA, Singapore, China and the Institute of
Interdisciplinary Physics and Complex Systems IFISC (UIB-CSIC) has appeared in a high-impact
journal where the authors report a new method to quantify the importance of
electrostatic interactions in molecular transistors. The proposed methodology is based on
the molecule's response to a magnetic field. This response is shown to be different
depending on whether Coulomb interactions are weak or strong. In the case of a molecule
exhibiting strong Coulomb interactions, the magnetic field shifts the molecular energy
levels. On the other hand, molecular junctions with negligible Coulomb interactions show
energy levels that split with increasing magnetic field. This differing response makes it possible to determine whether a molecular transistor is influenced by electronic
interactions. The measurements were performed using ferrocene molecular compounds
and good agreement between theory and experiment was found. Thereby, this work may
represent a significant advance in the precise characterization of molecular transistors.
Miguel A. Sierra, David Sanchez, Alvar R. Garrigues, Enrique del Barco, Lejia Wang, Christian A.
Nijhuis. Nanoscale. DOI: 10.1039/c7nr05739c
