Large-Amplitude, High-Frequency Single-Molecule Switch

Abstract

We use a scanning tunneling microscope to form and electrically interrogate metal - molecule - metal junctions. To form such junctions, molecules must be functionalised with suitable contact groups (e.g. thiols, thioethers, 4-pyridyls, amines) at each extremity. We show here that 2-(methylthio)thiophene units not only act as contact groups, but can reversibly switch between a monodentate configuration (MeS-only) and a bidentate configuration (MeS- and thienyl S) upon junction compression; as the junction is compressed the electrical conductance increases greatly with the increased molecule-contact interaction. This means that such molecules show a large-amplitude mechanical switching behavior; we also show that this is reversible and that switching can occur at a rate of at least 10 kHz. Control molecules with MeSC6H5 contact groups do not show this behavior. This, together with detailed theoretical and transport calculations on the compressed and extended molecular junctions, supports our contention that it is the thienyl S that is involved in the switching mechanism. <br>

Tuning the thermoelectrical properties of anthracene-based self-assembled monolayers

“…S29 and S30, † since the sign of the Seebeck coefficient is determined by the slope of the transmission coefficient near the Fermi energy, this switching from HOMO to LUMO-dominated transport causes the sign of Seebeck coefficient to change. LUMO-dominate transport was also predicted for the thioether-terminated molecules in ref. 41 , and measured experimentally for the longest molecule in ref.…”

Single-Molecule Junction Origami

“…We can rule out any contributions from variations in the molecule-electrode interface as a mechanism for the observed switching phenomena, as we have already demonstrated that thioanisole contacts do not change binding configuration upon junction compression. [20] Similarly, we can discount an interpretation of our results based on the formation of shorter junctions through Au-carbonyl contacts, as no interactions between a (di)ketone and gold electrodes (e.g. in measurements of molecular wires containing fluorenones, [30] anthraquinones [31] or diketopyrrolopyrroles [32] ) have been reported.…”

“…Junctions were fabricated and characterised using the STM-BJ technique, [1] using a modified Keysight 5500 STM. Further details on the equipment used, the data acquisition process and its analysis are available in our previous publications on the subject [19,20] and in the SI.…”

“…[12][13][14][15][16][17] As the stacking configuration is unfolded, conductance is predicted to drop by orders of magnitude, as tunnelling through a saturated propyl chain is very inefficient. Such a device would represent a new class of molecular electronic devices responsive to mechanical stimuli, complementing the existing range that exploits changes in the electrodemolecule interface, [18][19][20][21][22][23][24] stereoelectronic configuration switching, [25] and stretching-dependent quantum interference effects [12,26] as the molecular junction is compressed and relaxed. Intrigued by these phenomena, we designed molecule 1 to have two phenyl rings spaced by a diketone chain.…”

“…The molecule is therefore allowed to assemble in the gap in its thermodynamically favoured anti state, and it is then mechanically folded into the syn conformation by compressing the junction. More information on the piezo-modulation experiments can be found in our previous publications on the subject [19,20] and details are provided in the SI. Under a modulation amplitude of 0.4 nm the junctions could be cycled reliably from the high-to the low-conformation, with excellent repeatability (Figure 2d).…”