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Mechanically controlled molecular orbital alignment in single molecule junctions

Nature Nanotechnology volume 7, pages 35–40 (2012)Cite this article

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Abstract

Research in molecular electronics often involves the demonstration of devices that are analogous to conventional semiconductor devices, such as transistors and diodes1, but it is also possible to perform experiments that have no parallels in conventional electronics. For example, by applying a mechanical force to a molecule bridged between two electrodes, a device known as a molecular junction, it is possible to exploit the interplay between the electrical and mechanical properties of the molecule to control charge transport through the junction2,3,4,5,6,7,8. 1,4′-Benzenedithiol is the most widely studied molecule in molecular electronics9,10,11,12,13,14,15,16,17,18, and it was shown recently that the molecular orbitals can be gated by an applied electric field11. Here, we report how the electromechanical properties of a 1,4′-benzenedithiol molecular junction change as the junction is stretched and compressed. Counterintuitively, the conductance increases by more than an order of magnitude during stretching, and then decreases again as the junction is compressed. Based on simultaneously recorded current–voltage and conductance–voltage characteristics, and inelastic electron tunnelling spectroscopy, we attribute this finding to a strain-induced shift of the highest occupied molecular orbital towards the Fermi level of the electrodes, leading to a resonant enhancement of the conductance. These results, which are in agreement with the predictions of theoretical models14,15,16,17,19,20, also clarify the origins of the long-standing discrepancy between the calculated and measured conductance values of 1,4′-benzenedithiol, which often differ by orders of magnitude21.

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Figure 1: Changes in conductance of BDT due to stretching.
Figure 2: Differential conductance and IETS of BDT junctions as a result of stretching and compressing.
Figure 3: Conductance switching behaviour of two BDT junctions.
Figure 4: Exploring the energy levels of a molecular junction.

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Acknowledgements

This work was supported by the Basic Energy Science programme of the Department of Energy (DE-FG03-01ER45943, C.B.) and the National Science Foundation (CHE-1105588 and ECS-0925498, J.H. and N.J.T.).

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Authors and Affiliations

  1. Center for Bioelectronics and Biosensors, Biodesign Institute, School of Electrical, Energy and Computer Engineering, Arizona State University,

    Christopher Bruot, Joshua Hihath & Nongjian Tao

  2. Tempe, 85287-5801, Arizona, USA

    Christopher Bruot, Joshua Hihath & Nongjian Tao

  3. Department of Electrical and Computer Engineering, University of California Davis, Davis, 95616, California, USA

    Joshua Hihath

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  1. Christopher Bruot
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  3. Nongjian Tao
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Contributions

N.J.T. conceived the experiment. C.B. and J.H. performed the experiment and analysed the data. C.B., J.H. and N.J.T. co-wrote the paper.

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Correspondence to Nongjian Tao.

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The authors declare no competing financial interests.

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Bruot, C., Hihath, J. & Tao, N. Mechanically controlled molecular orbital alignment in single molecule junctions. Nature Nanotech 7, 35–40 (2012). https://doi.org/10.1038/nnano.2011.212

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