Abstract
Self-assembled monolayers of alkanethiols on gold are often used as a benchmark for molecular junctions, particularly as a reference for length-dependence. However, their thermopower decreases with molecular length and is bifurcated. While the bifurcation can be explained by the presence of gateway states, the length-dependence directly contradicts theoretical predictions. We reproduced both experimentally using conical tips of eutectic Ga-In (EGaIn) to form junctions. We then show that this unusual length-dependence arrises from the direction of the applied thermal gradient; when the gold substrate is cooled instead of heated, thermopower increases with length monotonically as predicted by theory. This unprecedented relationship between length-dependence and direction of thermal gradient persists over a very large range of absolute temperature. We therefore ascribe it to shifts in level-alignment induced by the electric field in the leads, which is present experimentally, neglected in theoretical modeling and is determined by the direction of the thermal gradient.
Original language | English |
---|---|
Article number | d4tc03895a |
Pages (from-to) | 1272-1280 |
Number of pages | 9 |
Journal | Journal of Materials Chemistry C |
Volume | 13 |
Issue number | 3 |
Early online date | 15-Nov-2024 |
DOIs | |
Publication status | Published - 21-Jan-2025 |