A single atom change turns insulating saturated wires into molecular conductors.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 34103489.
- Also identified by DOI 10.1038/s41467-021-23528-8 and PMC identifier 8187423.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
We present an efficient strategy to modulate tunnelling in molecular junctions by changing the tunnelling decay coefficient, β, by terminal-atom substitution which avoids altering the molecular backbone. By varying X = H, F, Cl, Br, I in junctions with S(CH<sub>2</sub>)<sub>(10-18)</sub>X, current densities (J) increase >4 orders of magnitude, creating molecular conductors via reduction of β from 0.75 to 0.25 Å<sup>-1</sup>. Impedance measurements show tripled dielectric constants (ε<sub>r</sub>) with X = I, reduced HOMO-LUMO gaps and tunnelling-barrier heights, and 5-times reduced contact resistance. These effects alone cannot explain the large change in β. Density-functional theory shows highly localized, X-dependent potential drops at the S(CH<sub>2</sub>)<sub>n</sub>X//electrode interface that modifies the tunnelling barrier shape. Commonly-used tunnelling models neglect localized potential drops and changes in ε<sub>r</sub>. Here, we demonstrate experimentally that [Formula: see text], suggesting highly-polarizable terminal-atoms act as charge traps and highlighting the need for new charge transport models that account for dielectric effects in molecular tunnelling junctions.