Voltage-Modulated van der Waals Interaction in Single-Molecule Junctions

Abstract

Understanding how molecular geometry affects the electronic properties of single-molecule junctions experimentally has been challenging. Typically, metal− molecule−metal junctions are measured using a break-junction method where electrode separation is mechanically evolving during measurement. Here, to probe the impact of the junction geometry on conductance, we apply a sinusoidal modulation to the molecular junction electrode position. Simultaneously, we probe the nonlinearity of the current−voltage characteristics of each junction through a modulation in the applied bias at a different frequency. In turn, we show that junctions formed with molecules that have different molecule−electrode interfaces exhibit statistically distinguishable Fourier-transformed conductances. In particular, we find a marked bias dependence for the modulation of junctions where transmission is mediated thorough the van der Waals (vdW) interaction. We attribute our findings to voltage-modulated vdW interactions at the singlemolecule level.

Robust Single-Supermolecule Switches Operating in Response to Two Different Noncovalent Interactions

“…Our findings indicate that both states are indicative of throughspace charge transport. These observations are consistent with the charge transport mechanism that (i) the HC state�with a molecular length of ∼0.70 nm�can be attributed 65,66 to the conducting feature of the monomer that binds to electrodes through Au−SMe on one end and weak Au−π interactions on the other end, and (ii) the HC&LC state�with a molecular length of ∼1.14 nm�can be attributed 23 to the intermolecular charge transport through [π•••π] dimer junctions. In order to confirm that the HC state can be attributed to Au−π interactions, we conducted (Figure S42) I−V curve fittings, which yielded a coupling constant of 0.07 eV.…”

Evolution of Single-Molecule Electronic Interfaces

“…This above through-space mechanism via non-covalent interfaces was further confirmed by the PSD method in Figure e. Moreover, this non-covalent van der Waals interaction also exhibits an electric field modulation effect at the single-molecule level . Stoddart et al reported a new anchoring strategy, named the electrostatic anchor, via the non-covalent Coulombic interaction between the gold electrodes and the positively charged pyridinium terminal groups (Figure e) .…”

Intermolecular and Electrode-Molecule Bonding in a Single Dimer Junction of Naphthalenethiol as Revealed by Surface-Enhanced Raman Scattering Combined with Transport Measurements

“…Noncovalent interactions play a decisive role in a self-assembly process in organic, inorganic, and biological materials. − The combination of the interactions enables sophisticated structural design for a wide range of nanomaterials and construction of superior systems for molecular recognition. − In particular, electron transport through the π–π interaction in π-conjugated molecular systems has attracted significant attention to build novel electronic materials taking advantage of the unique delocalized electric states intrinsic to the constituent molecules. , For example, the efficient long-range charge transport via π–π interactions makes DNA promising building blocks in ultrasmall electronic materials . The availability of the quantum interference effect − to control the electron transport gives the π-conjugated systems an additional advantage in electronics applications.…”