Liquid metals have attracted attention as functional components for moldable electronics, such as soft flexible connectors, wires or conductive ink. The relatively high surface tension (> 400 mN m−1) and the fact that liquid metals do not readily wet ceramic or oxide surfaces have led to devising unique techniques to spread the liquid and mold its shape. These techniques include surface modification, electrowetting and vacuum filling of channels. This work presents an injection technique based on pressurized fountain pen lithography with glass nanopipettes developed to directly pattern liquid metal on flat hard substrates. The liquid metals were eutectic alloys of Gallium, including Gallium-Indium (EGaIn), Gallium-Indium-Zinc and Gallium-Indium-Tin. The nanopipettes were coated internally with gold, acting as a sacrificial layer and facilitating the wetting of the pipette down to its pore, with an inner diameter of ~ 100–300 nm. By applying hydrodynamic pressure to the connected end of the pipette, the metal was extruded through the pore, forming long continuous (> 3 mm) and narrow (~ 1–15 µm) metal lines on silicon oxide and gold surfaces at room temperature and ambient conditions. With this robust platform, it is possible to pattern liquid metals on a variety of substrates and geometries down to the micron range.

Current−voltage (I−V) nonlinearity is essential for information processing in molecular electronics. We used a nanoparticle bridge junction to investigate the effect of electronic coupling between a Ru complex and electrodes on nonlinear electrical properties. Two types of molecular layers, in which the Ru complex forms different chemical bondings to the electrode, were used for electrical measurements. The chemical bond and the surface potential of the Ru complex on Au electrodes were examined by X-ray photoelectron spectroscopy, infrared ray reflection absorbance spectroscopy and Kelvin probe force microscopy, respectively. The device, in which the Ru complex is directly bound to the Au electrode, indicated the nonlinear I−V characteristics with zero-bias conductance because of the direct tunneling conduction. Another device fabricated by inserting a spacer molecule between the Ru complex and the Au electrode realized nonlinear I−V characteristics with a clear threshold voltage and little zero-bias conductance. The I−V curves were well fitted by the resonant tunneling conduction model. The present results show the significance of controlling the electronic coupling for nonlinear I−V characteristics.

Kelvin probe force microscopy (KPFM) is a valuable technique for visualizing local surface potential with high spatial resolution, although it is incapable of providing the absolute value of the surface potential owing to the unknown condition of the tip, which serves as a potential reference. Owing to these uncontrollable variations in the tip properties, KPFM is of limited utility for comparing the surface potential between different single-component sample surfaces. This paper describes a statistical method for analyzing the variation of the contact potential difference during KPFM measurements.

Electric conduction through Ru-complex self-assembled monolayer (SAM) was investigated by Au-nanoparticle (AuNP) bridge junction. Nonlinear current-voltage (I-V) characteristics exhibiting sharp threshold and steep rise with no zero-bias conductance was achieved by weak coupling between electrode and molecules. The observed I-V characteristics were well fitted by resonant tunneling model via HOMO level in wide range of temperature. The analysis by this curve fitting reveals that the work function of Au-nanoparticles was 0.32 eV larger than Au electrode and the thickness of SAM layer of tunneling barrier decrease as increasing temperature.