Tunneling Junctions on Transparent ITO Electrodes Using Phosphonic Acids for Surface Modification

Since the 1980s, self-assembled monolayers (SAMs) have been used to investigate the electronic properties of molecules in ensemble junctions. They are often formed by contacting a monolayer supported by a planar gold electrode with a conformal metal such as Eutectic Gallium Indium (EGaIn). This material is a non-Newtonian liquid metal alloy, allowing us to form multiple junctions on a single sample in a non-destructive manner. Due to these reasons, replacing the EGain electrode for something transparent is not plausible, so instead we target the planar electrode. Suitable candidates for this are transparent conducting oxides (TCOs). We opted for Indium Tin Oxide (ITO) as it is well known, well studied and important in the field of solar cells and diodes.<br/>We formed monolayers of alkyl phosphonates with varying chain lengths and measured the current-voltage characteristics and observed two different regimes of tunneling decay and possibly two regimes of odd-even effect in the monolayers.