Comparison of SAM-Based Junctions with Ga2O3/EGaIn Top Electrodes to Other Large-Area Tunneling Junctions

Christian A Nijhuis,George M Whitesides,Jabulani R Barber,William F Reus

doi:10.1021/jp303072a

Abstract

This paper compares the J(V) characteristics obtained for self-assembled monolayer (SAM)-based tunneling junctions with top electrodes of the liquid eutectic of gallium and indium (EGaIn) fabricated using two different procedures: (i) stabilizing the EGaIn electrode in PDMS microchannels and (ii) suspending the EGaIn electrode from the tip of a syringe. These two geometries of the EGaIn electrode (with, at least when in contact with air, its solid Ga2O3 surface film) produce indistinguishable data. The junctions incorporated SAMs of SCn–1CH3 (with n = 12, 14, 16, or 18) supported on ultraflat, template-stripped silver electrodes. Both methods generated high yields of junctions (70–85%) that were stable enough to conduct measurements of J(V) with statistically large numbers of data (N = 400–1000). The devices with the top electrode stabilized in microchannels also made it possible to conduct measurements of J(V) as a function of temperature, almost down to liquid nitrogen temperatures (T = 110–293 K). The ...

Highlights

This paper compares the electrical characteristics obtained for two types of tunneling junctions, both comprising template-stripped silver bottom electrodes (AgTS), self-assembled monolayers (SAMs), with top-electrodes of a liquid eutectic alloy of indium and gallium (EGaIn); in one junction, the EGaIn is stabilized in microchannels;[1] in the second, it is suspended as a drop with a cone-shaped tip from a syringe:[2] the paper compares these electrical measurements to those obtained with other types of socalled “large-area tunneling junctions”
To avoid the limitations of the junctions with cone-shaped tips of Ga2O3/EGaIn suspended from a syringe, we fabricated silver micro-electrodes supporting SAMs, positioned microchannels molded in polydimethylsiloxane (PDMS) over these micro-electrodes, and filled the microchannels with EGaIn.[1]
We compare data obtained from junctions with topelectrodes of cone-shaped tips of Ga2O3/EGaIn with data obtained from junctions with top-electrodes of Ga2O3/EGaIn stabilized in microchannels

Summary

Introduction

This paper compares the electrical characteristics obtained for two types of tunneling junctions, both comprising template-stripped silver bottom electrodes (AgTS), self-assembled monolayers (SAMs), with top-electrodes of a liquid eutectic alloy of indium and gallium (EGaIn); in one junction, the EGaIn is stabilized in microchannels;[1] in the second, it is suspended as a drop with a cone-shaped tip from a syringe:[2] the paper compares these electrical measurements to those obtained with other types of socalled “large-area tunneling junctions” (e.g., junctions that contain SAMs rather than single molecules[3]). We compare the values of J, J0, and β obtained in this work with values reported in the literature for other systems (see below), to try to identify consensus values for β (and perhaps for J0), and to determine the reliability of our methods for constructing SAM-based junctions. These results are important in establishing the validity of Ga2O3/EGaIn-based junctions in physical-organic studies of charge transport across these junctions.[5,6,7]

Background

Results and Discussion

Conclusions