A comprehensive understanding of carrier transport in photoisomeric molecular junctions is crucial for the rational design and delicate fabrication of single-molecule functional devices. It has been widely recognized that the conductance of azobenzene (a class of photoisomeric molecules) based molecular junctions is mainly determined by photoinduced conformational changes. In this study, it is demonstrated that the most probable conductance of amine-anchored azobenzene-based molecular junctions increases continuously upon UV irradiation. In contrast, the conductance of pyridyl-anchored molecular junctions with an identical azobenzene core exhibits a contrasting trend, highlighting the pivotal role that anchoring groups play, potentially overriding (even reversing) the effects of photoinduced conformational changes. It is further demonstrated that the molecule with cis-conformation cannot be fully mechanically stretched into the trans-conformation, clarifying that it is a great challenge to realize a reversible molecular switch by purely mechanical operation. Additionally, it is revealed that the coupling strength of pyridyl-anchored molecules is dramatically weakened when the UV irradiation time is prolonged, whereas it is not observed for amine-anchored molecules. The mechanisms for these observations are elucidated with the assistance of density functional theory calculations and UV-Vis spectra combined with flicker noise measurements which confirm the photoinduced conformational changes, providing insight into understanding the charge transport in photoisomeric molecular junctions and offering a routine for logical designing synchro opto-mechanical molecular switches.

In electronic functional chips, one of the most crucial components is the field-effect transistor (FET). To meet the urgent demands for further miniaturization of electronic devices, solid-state single-molecule transistors by molecular orbital gating have been extensively reported. However, under negative bias and positive bias, achieving a distinct gating effect is extremely challenging because molecular orbital gating is independent of the bias polarity. Here, we demonstrated that rectifiers can be realized in single-molecule junctions with a symmetric molecular structure and an electrode material by simply breaking the symmetry of the electrode's chemical potential via ionic adsorption. We further demonstrated that the tunneling current can be gated with opposite change tendencies under negative and positive bias by applying an ionic gating voltage, which eventually results in a reversal of the rectifying direction. Our experiments elucidate that, unlike the classical mechanism for solid molecular FET, the modulation of the electrode's chemical potential, rather than the regulation of molecular orbitals, might dominate the electron transport in the ionic liquid environment upon a gating voltage. Our study gains deeper insights into the mechanism of ionic liquid gating and opens a window for designing high-performance electrochemical-based functional devices.

The manipulation of single molecules has attracted extensive attention because of their promising applications in chemical, biological, medical, and materials sciences. Optical trapping of single molecules at room temperature, a critical approach to manipulating the single molecule, still faces great challenges due to the Brownian motions of molecules, weak optical gradient forces of laser, and limited characterization approaches. Here, we put forward localized surface plasmon (LSP)-assisted trapping of single molecules by utilizing scanning tunneling microscope break junction (STM-BJ) techniques, which could provide adjustable plasmonic nanogap and characterize the formation of molecular junction due to plasmonic trapping. We find that the plasmon-assisted trapping of single molecules in the nanogap, revealed by the conductance measurement, strongly depends on the molecular length and the experimental environments, i.e., plasmon could obviously promote the trapping of longer alkane-based molecules but is almost incapable of acting on shorter molecules in solutions. In contrast, the plasmon-assisted trapping of molecules can be ignored when the molecules are self-assembled (SAM) on a substrate independent of the molecular length.

We propose a double-layer graphene sheets side coupling to a strip of graphene to obtain the optical pulling or pushing force. Combined with coupled mode theory and finite-difference time-domain simulations, it is found that the conveyor belt effect can be realized in conjunction with the lateral optical equilibrium effect upon the radiation loss κe equal to the intrinsic loss κo. The maximum total optical force acting on the strip in the symmetric mode (S-mode) can be up to ∼5.95 in the unit of 1/c and the anti-symmetric (AS-mode) mode reach ∼2.75 1/c. The optical trapping potential Ux and optical trapping force Fx for the S-mode have a value around -22.5 kBT/W and 240 pN/W, while for the AS-mode can up to ∼-56 kBT/W and 520 pN/W, respectively. Our work opens a new avenue for optical manipulation with potential applications in optoelectronic devices and lab-on-a-chip platforms.

We analytically and numerically investigate the acoustic plasmon mode in phosphorene placed above a metallic substrate with a finite gap width. Combined with finite-difference time-domain simulations, we demonstrate the responses of evanescent waves in the phosphorene-insulator-metal (PIM) waveguide, involving field enhancement, light confinement, and optical force. It turned out that owing to a large amount of light energy squeezed inside the gap, the light confinement ratio and optical force along the armchair direction in the PIM waveguide can be up to 96% and 6930 pN mW−1, respectively. Our results may manifest in diverse optoelectronic applications like optical tweezers.