Hybrid Molecular-Junction Mapping Technique for Simultaneous Measurements of Single-Molecule Electronic Conductance and Its Corresponding Binding Geometry in a Tunneling Junction

Abstract

Improving the techniques for single-molecule conductance measurements is important for the progress of molecular electronics. In this report, a novel technique, which is named molecular-junction mapping (MJM) technique, is demonstrated to be able to simultaneously measure the electronic conductance of single molecules and their corresponding conformations in an electrode gap. Measured conductances of a few model molecules yield a much narrower distribution as compared with the results obtained using conventional break-junction technique, indicating that better defined metal–molecule contacts can be achieved using this new technique. In addition, multiple binding states of an alkanedithiol molecule in an electrode gap, which give rise to multiple conductance states, are efficiently revealed by this hybrid technique, with the results being consistent with those in former reports. This newly demonstrated technique opens up a new avenue for the study of single-molecule electronic properties and will instantly add significant assets to the tool library available for researchers in molecular electronics.

Developing Longer‐Lived Single Molecule Junctions with a Functional Flexible Electrode

“…Two‐level stochastic current fluctuations, arising from spontaneous binding and unbinding of single molecules with electrodes, [ 30,31 ] are frequently seen as shown in the insets of Figure a,b. The height of the current jumps (Δ I ) in the collected current time ( I – t ) traces for both types of probes are similar, reflecting similar single molecule conductance ( G = Δ I / V [ 17,32 ] ) can be obtained by both types of probes. However, the durations of the switching events in two cases are quite different, with the “on” states lasting obviously longer in the NPE recorded events.…”

“…A Au‐coated nanopipette electrode (NPE) is used as the tip of a home‐built STM on a gold substrate as described elsewhere. [ 14–17 ] The NPE is fabricated by sequentially depositing chromium and gold on a laser‐pulled quartz nanopipette (see Section S1.1, Supporting Information), and the produced electrode possesses a conducting exterior surface, an open channel and a long shank length (6.1 ± 0.1 mm) with a high flexibility [ 14 ] (k NP ≈ 0.13 N m −1 , see atomic force microscopy (AFM) measurement of the NPE spring constant in Section S2.1, Supporting Information). The optical image of a typical NPE and its SEM images of the tip apex are displayed in the inset of Figure 1a.…”

pH-Mediated Single Molecule Conductance of Cucurbit[7]uril

“…Generally, a gold probe is placed in close proximity to gold surface functionalized with the target molecule where the distance between the probe and the substrate is fixed at a few tens of nanometers controlled by the piezoelectric transducer (PZT) of a STM. The target molecules are not disturbed by electrodes moving or crashing into each other, which makes it suitable for the study of noncovalent interactions between single molecules (Chen et al, 2020 ). No signal was observed on clean gold substrate (black curve of Figure 1B ) or on gold surface modified with CB[7] where no effective molecular junctions form (“off” state).…”

“…Molecular electronics aims at investigating single molecules at electrical junctions for fabricating electronic devices, which has been extensively investigated (Cui, 2001;Choi and Mody, 2009;Herrer et al, 2018). A variety of methods have been developed to measure the electrical properties of single molecules by constructing metal-moleculemetal junctions, including scanning probes techniques such as scanning tunneling microscopy (STM) techniques (Xu and Tao, 2003;Haiss et al, 2006;Venkataraman et al, 2006;Chen et al, 2020;Yu et al, 2020), conducting atomic force microscopy (AFM) (Cui, 2001), mechanically controlled break junctions (MCBJ) (Reed et al, 1997;Smit et al, 2002), and nanoparticle dimers (Dadosh et al, 2005;Fernandez et al, 2014).…”

The effect of non-covalent conformational locks on intra-molecular charge transport of OPV units

“…Single molecular conductance measurement (SMCM) is a powerful tool to examine the charge transport properties of single molecules between two metal electrodes, such as mechanically controlled break junction (MCBJ), 17 scanning tunnelling microscopy (STM) based break junction (BJ) 18,19 and fixed junction (FJ) 20 techniques. As an important prerequisite for carrying out such research, introducing extra linker groups into the target molecules was required to form stable and robust metal-molecule linkage, 18 b dedicated to ensuring reproducible junction formation.…”