Scale-Up of Room-Temperature Constructive Quantum Interference from Single Molecules to Self-Assembled Molecular-Electronic Films.

Xintai Wang,Lesley F Cohen,Tim Albrecht,Nicholas J Long,Ali Ismael,Luke A Wilkinson,Oleg V Kolosov,Benjamin J Robinson,Colin J Lambert,Iain M Grace,Andrew J P White,Troy L R Bennett,Joseph Hamill

doi:10.1021/jacs.9b13578

Abstract

The realization of self-assembled molecular-electronic films, whose room-temperature transport properties are controlled by quantum interference (QI), is an essential step in the scale-up of QI effects from single molecules to parallel arrays of molecules. Recently, the effect of destructive QI (DQI) on the electrical conductance of self-assembled monolayers (SAMs) has been investigated. Here, through a combined experimental and theoretical investigation, we demonstrate chemical control of different forms of constructive QI (CQI) in cross-plane transport through SAMs and assess its influence on cross-plane thermoelectricity in SAMs. It is known that the electrical conductance of single molecules can be controlled in a deterministic manner, by chemically varying their connectivity to external electrodes. Here, by employing synthetic methodologies to vary the connectivity of terminal anchor groups around aromatic anthracene cores, and by forming SAMs of the resulting molecules, we clearly demonstrate that this signature of CQI can be translated into SAM-on-gold molecular films. We show that the conductance of vertical molecular junctions formed from anthracene-based molecules with two different connectivities differ by a factor of approximately 16, in agreement with theoretical predictions for their conductance ratio based on CQI effects within the core. We also demonstrate that for molecules with thioether anchor groups, the Seebeck coefficient of such films is connectivity dependent and with an appropriate choice of connectivity can be boosted by ∼50%. This demonstration of QI and its influence on thermoelectricity in SAMs represents a critical step toward functional ultra-thin-film devices for future thermoelectric and molecular-scale electronics applications.

Highlights

Molecular electronic devices have the potential to deliver logic gates, sensors, memories, and thermoelectric energy harvesters with ultra-low power requirements and sub-10-nm device footprints.[1−4] Single-molecule electronic junctions[5−12] and self-assembled monolayers (SAMs)[13−15] have been investigated intensively over the past few years, because their room-temperature electrical conductance has been shown to be controlled by destructive quantum interference (DQI).[16−20] More recently the effect of quantum interference (QI) on the Seebeck coefficient of single molecules has been studied.[21−26] Figure 1A illustrates an example where a room-temperature constructive quantum interference (CQI) effect would be expected from an anthracene molecular core
Our aim is to create SAMs from these compounds, demonstrate that these single-molecule signatures of CQI can be translated into SAM-based devices, and assess the effect of CQI on their Seebeck coefficients
We find that the electrical conductances of SAMs formed from 1 and 3 are significantly higher than those of SAMs formed from 2 and 4

Summary

Corresponding Authors

Long − Department of Chemistry, Imperial College London, MSRH, White City, London W12 0BZ, U.K.; orcid.org/0000-0002-8298-938X; Email: n.long@ imperial.ac.uk. Xintai Wang − Physics Department, Lancaster University, Lancaster LA1 4YB, U.K.; The Blackett Laboratory, Imperial College London, London SW7 2AZ, U.K. Troy L. R. Bennett − Department of Chemistry, Imperial College London, MSRH, White City, London W12 0BZ, U.K. Ali Ismael − Physics Department, Lancaster University, Lancaster LA1 4YB, U.K.; Department of Physics, College of Education for Pure Science, Tikrit University, Tikrit, Iraq. Wilkinson − Department of Chemistry, Imperial College London, MSRH, White City, London W12 0BZ, U.K.; orcid.org/0000-0002-8550-3226. P. White − Department of Chemistry, Imperial College London, MSRH, White City, London W12 0BZ, U.K. Iain M. Kolosov − Physics Department, Lancaster University, Lancaster LA1 4YB, U.K.; orcid.org/0000-0003-32789643. Tim Albrecht − Department of Chemistry, Birmingham University, Edgbaston, Birmingham B15 2TT, U.K.; orcid.org/0000-0001-6085-3206. Author Contributions #X.W., T.L.R.B., and A.I. contributed

■ ACKNOWLEDGMENTS

■ REFERENCES

Transport through Polycyclic Aromatic Hydrocarbons with Different