Galinstan Liquid Metal Electrical Contacts for Monolayer-Modified Silicon Surfaces

Galinstan is the brand name for a low-melting gallium-based alloy, which is a promising nontoxic alternative to mercury, the only elemental metal found in the liquid state at room temperature. Liquid alloys such as Galinstan have found applications as electromechanical actuators, sensors, and soft contacts for molecular electronics. In this work, we validate the scope of Galinstan top contacts to probe the electrical characteristics of Schottky junctions made on Si(111) and Si(211) crystals modified with Si-C-bound organic monolayers. We show that the surface-to-volume ratio of the Galinstan drop used as a macroscopic contact defines the junction stability. Further, we explore chemical strategies to increase Galinstan surface tension to obtain control over the junction area, hence improving the repeatability and reproducibility of current-voltage (I-V) measurements. We explore Galinstan top contacts as a means to monitor changes in rectification ratios caused by surface reactions and use these data, most notably the static junction leakage, toward making qualitative predictions on the DC outputs recorded when these semiconductor systems are incorporated in Schottky-based triboelectric nanogenerators. We found that the introduction of iron particles leads to poor data repeatability for capacitance-voltage (C-V) measurements but has only a small negative impact in a dynamic current measurement (I-V).