Bias induced transition from an ohmic to a non-ohmic interface in supramolecular tunneling junctions with Ga2O3/EGaIn top electrodes

Kim S. Wimbush, Raluca M. Fratila, Dandan Wang, Dongchen Qi, Cao Liang, Li Yuan, Nikolai Yakovlev, Kian Ping Loh, David N. Reinhoudt, Aldrik H. Velders, Christian A. Nijhuis
2014 Nanoscale  
This study describes that the current rectification ratio, R h |J|(À2.0 V)/|J|(+2.0 V) for supramolecular tunneling junctions with a top-electrode of eutectic gallium indium (EGaIn) that contains a conductive thin (0.7 nm) supporting outer oxide layer (Ga 2 O 3 ), increases by up to four orders of magnitude under an applied bias of >+1.0 V up to +2.5 V; these junctions did not change their electrical characteristics when biased in the voltage range of AE1.0 V. The increase in R is caused by the
more » ... R is caused by the presence of water and ions in the supramolecular assemblies which react with the Ga 2 O 3 /EGaIn layer and increase the thickness of the Ga 2 O 3 layer. This increase in the oxide thickness from 0.7 nm to $2.0 nm changed the nature of the monolayer-top-electrode contact from an ohmic to a non-ohmic contact. These results unambiguously expose the experimental conditions that allow for a safe bias window of AE1.0 V (the range of biases studies of charge transport using this technique are normally conducted) to investigate molecular effects in molecular electronic junctions with Ga 2 O 3 /EGaIn top-electrodes where electrochemical reactions are not significant. Our findings also show that the interpretation of data in studies involving applied biases of >1.0 V may be complicated by electrochemical side reactions which can be recognized by changes of the electrical characteristics as a function voltage cycling or in current retention experiments. † Electronic supplementary information (ESI) available: Nomenclature, synthesis of compounds, preparation of supramolecular tunneling junctions, J(V) measurements of tunneling junctions, J(V) characteristics of oxidized Ga 2 O 3 /EGaIn tips, Kelvin probe measurements, photoelectron spectroscopy and ellipsometry measurements. See
doi:10.1039/c4nr02933j pmid:25132523 fatcat:4x4xusmcavf7pp3r7lyvfwfdla