The Characterization of Electronic Noise in the Charge Transport through Single-Molecule Junctions

Unveiling the Properties of Sulfhydryl Groups in a Single-Molecule Junction

The metal-thiol interface is ubiquitous in nanotechnology and surface chemistry. It is not only used to construct nanocomposites but also plays a decisive role in the properties of these materials. When organothiol molecules bind to the gold surface, there is still controversy over whether sulfhydryl groups can form disulfide bonds and whether these disulfide bonds can remain stable on the gold surface. Here, we investigate the intrinsic properties of sulfhydryl groups on the gold surface at the single-molecule level using a scanning tunneling microscope break junction technique. Our findings indicate that sulfhydryl groups can react with each other to form disulfide bonds on the gold surface, and the electric field can promote the sulfhydryl coupling reaction. In addition to these findings, ultraviolet irradiation is used to effectively regulate the coupling between sulfhydryl groups, leading to the formation and cleavage of disulfide bonds. These results unveil the intrinsic properties of sulfhydryl groups on the gold surface, therefore facilitating the accurate construction of broad nanocomposites with the desired functionalities.

Characterization and Application of Supramolecular Junctions

The convergence of supramolecular chemistry and single-molecule electronics offers a new perspective on supramolecular electronics, and provides a new avenue toward understanding and application of intermolecular charge transport at the molecular level. In this review, we will provide an overview of the advances in the characterization technique for the investigation of intermolecular charge transport, and summarize the experimental investigation of several non-covalent interactions, including π-π stacking interactions, hydrogen bonding, host-guest interactions and σ-σ interactions at the single-molecule level. We will also provide a perspective on supramolecular electronics and discuss the potential applications and future challenges.

Quantum Flicker Noise in Atomic and Molecular Junctions

We report on a quantum form of electronic flicker noise in nanoscale conductors that contains valuable information on quantum transport. This noise is experimentally identified in atomic and molecular junctions and theoretically analyzed by considering quantum interference due to fluctuating scatterers. Using conductance, shot-noise, and flicker-noise measurements, we show that the revealed quantum flicker noise uniquely depends on the distribution of transmission channels, a key characteristic of quantum conductors. This dependence opens the door for the application of flicker noise as a diagnostic probe for fundamental properties of quantum conductors and many-body quantum effects, a role that up to now has been performed by the experimentally less-accessible shot noise.

The Evolution of the Charge Transport Mechanism in Single-Molecule Break Junctions Revealed by Flicker Noise Analysis

The electronic noise characterization of single-molecule devices provides insights into the mechanisms of charge transport. In this work, it is reported that flicker noise can serve as an indicator of the time-dependent evolution of charge transport mechanisms in the single-molecule break junction process. By introducing time-frequency analysis, the authors find that flicker noise components of the molecule junction show time evolution behavior in the dynamic break junction process. A further investigation of the power-law dependence of flicker with conductance during the dynamic break junction process reveals that the mechanism of charge transport transits from the through-space transport to the through-bond transport, and is dominated by through-space transport again when the junction is about to rupture. The authors' results provide a flicker noise-based way to characterize the time-dependent evolution of charge transport mechanisms in single-molecule break junctions.

Universal Bounds on Fluctuations in Continuous Thermal Machines

We study bounds on ratios of fluctuations in steady-state time-reversal energy conversion devices. In the linear response regime, we prove that the relative fluctuations (precision) of the output current (power) is always lower bounded by the relative fluctuations of the input current (heat current absorbed from the hot bath). As a consequence, the ratio between the fluctuations of the output and input currents are bounded both from above and below, where the lower (upper) bound is determined by the square of the averaged efficiency (square of the Carnot efficiency) of the engine. The saturation of the lower bound is achieved in the tight-coupling limit when the determinant of the Onsager response matrix vanishes. Our analysis can be applied to different operational regimes, including engines, refrigerators, and heat pumps. We illustrate our findings in two types of continuous engines: two-terminal coherent thermoelectric junctions and three-terminal quantum absorption refrigerators. Numerical simulations in the far-from-equilibrium regime suggest that these bounds apply more broadly, beyond linear response.