Influence of Environment on the Measurement of Ratesof Charge Transport across AgTS/SAM//Ga2O3/EGaIn Junctions.

Thispaper investigates the influence of the atmosphere used inthe fabrication of top electrodes from the liquid eutectic of galliumand indium (EGaIn) (the so-called “EGaIn” electrodes),and in measurements of current density, J(V) (A/cm2), across self-assembled monolayers (SAMs) incorporated intoAg/SR//Ga2O3/EGaIn junctions, on values of J(V) obtained using these electrodes. A gas-tight measurementchamber was used to control the atmosphere in which the electrodeswere formed, and also to control the environment in which the electrodeswere used to measure current densities across SAM-based junctions.Seven different atmospheresair, oxygen, nitrogen, argon, andammonia, as well as air containing vapors of acetic acid or waterweresurveyed using both “rough” conical-tip electrodes,and “smooth” hanging-drop electrodes. (The manipulationof the oxide film during the creation of the conical-tip electrodesleads to substantial, micrometer-scale roughness on the surface ofthe electrode, the extrusion of the drop creates a significantly smoothersurface.) Comparing junctions using both geometries for the electrodes,across a SAM of n-dodecanethiol, in air, gave log |J|mean= −2.4 ± 0.4 for the conicaltip, and log |J|mean= −0.6± 0.3 for the drop electrode (and, thus, Δlog |J| ≈ 1.8); this increase in current density is attributedto a change in the effective electrical contact area of the junction.To establish the influence of the resistivity of the Ga2O3film on values of J(V), junctionscomprising a graphite electrode and a hanging-drop electrode werecompared in an experiment where the electrodes did, and did not, havea surface oxide film; the presence of the oxide did not influencemeasurements of log |J(V)|, and therefore did notcontribute to the electrical resistance of the electrode. However,the presence of an oxide film did improve the stability of junctionsand increase the yield of working electrodes from ∼70% to ∼100%.Increasing the relative humidity (RH) in which J(V)was measured did not influence these values (across methyl (CH3)- or carboxyl (CO2H)-terminated SAMs) over therange typically encountered in the laboratory (20%–60% (RH)). [ABSTRACT FROM AUTHOR]