Influence of air-oxidation on rectification in thiol-based molecular monolayers

Spontaneous structural degradation processes occurring on metallic surfaces upon exposure to air-self-passivation-are well known for conventional silicon-based electronic materials; however, the effect of the analogous process for organic materials inside molecular electronic devices on their electrical behavior is rarely understood. Here, we show the influence of air-oxidation on molecular rectification in large-area junctions formed from a self-assembled monolayer (SAM) comprising 2,2′-bipyridyl terminated n-alkanethiolate. Upon exposure to air, the rectification ratio decreases as a function of air-exposure time and disappears in ∼3 h. Structural analyses of the SAM using X-ray photoelectron spectroscopy and wet electrochemistry, as well as several physical-organic studies indicate that the decrease of rectification over time stems from structural degradation, facilitated by light, of the thiolate anchoring group of the SAM.