Abstract
It is known that the electrical conductance of single molecules can be controlled in a deterministic manner by chemically varying their anchor groups to external electrodes. Here, by employing synthetic methodologies to vary the terminal anchor groups around aromatic anthracene cores, and by forming self-assembled monolayers (SAMs) of the resulting molecules, we demonstrate that this method of control can be translated into cross-plane SAM-on-gold molecular films. The cross-plane conductance of SAMs formed from anthracene-based molecules with four different combinations of anchors are measured to differ by a factor of approximately 3 in agreement with theoretical predictions. We also demonstrate that the Seebeck coefficient of such films can be boosted by more than an order of magnitude by an appropriate choice of anchor groups and that both positive and negative Seebeck coefficients can be realised. This demonstration that the thermoelectric properties of SAMs are controlled by their anchor groups represents a critical step towards functional ultra-thin-film devices for future molecular-scale electronics.
Highlights
All publication charges for this article have been paid for by the Royal Society of Chemistry
As highlighted in recent reviews,[18,19,20,21] Seebeck coefficients of single molecules can be controlled by varying the anchor groups,[22,23,24] which bind them to external electrodes; Seebeck coefficients of single molecules with thiol anchor groups are found to be positive, while those with pyridyl anchor groups are measured to be negative, with room-temperature magnitudes, which are typically a few tens of mV KÀ1 at room temperature
A recent study[25] shows nearly 2 orders of magnitude higher thermopowers than this value, the power generated by a single molecule is not yet sufficient to be of technological interest and there is a need to demonstrate that this single-molecule tunability can be scaled up into thin lms formed from self-assembled molecular arrays (SAMs).[26]
Summary
All publication charges for this article have been paid for by the Royal Society of Chemistry. By employing synthetic methodologies to vary the terminal anchor groups around aromatic anthracene cores, and by forming self-assembled monolayers (SAMs) of the resulting molecules, we demonstrate that this method of control can be translated into cross-plane SAM-on-gold molecular films. We demonstrate that the Seebeck coefficient of such films can be boosted by more than an order of magnitude by an appropriate choice of anchor groups and that both positive and negative Seebeck coefficients can be realised. This demonstration that the thermoelectric properties of SAMs are controlled by their anchor groups represents a critical step towards functional ultra-thin-film devices for future molecular-scale electronics. A recent study[25] shows nearly 2 orders of magnitude higher thermopowers than this value, the power generated by a single molecule is not yet sufficient to be of technological interest and there is a need to demonstrate that this single-molecule tunability can be scaled up into thin lms formed from self-assembled molecular arrays (SAMs).[26]
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