Diluting monolayers in molecular diodes to enhance their electrical properties

Abstract

We report on the electrical properties of a series of molecular rectifiers based on benzalkylsilane molecules in self-assembled monolayers (SAMs) anchored to silicon substrates with a native layer of SiO2. Mixed SAMs were formed via co-absorption where known amounts of aliphatic silane-based impurities were included into the rectifying SAMs. We discovered that in spite of the fact that the degree of order within the SAMs decreased upon dilution the impurity (3-aminopropyl)triethoxysilane enhanced the rectification for several SAMs. The largest change resulted in a three-fold increase for an average rectification of 4500; the highest reported rectification for SAMs assembled on silicon to date. We attribute this novel behavior to a new molecular configuration within the SAM that allows more efficient coupling between the delocalized electrons of the SAM and the device electrode. Understanding how to optimize SAMs will allow for more functionable, integrable and cost-efficient devices.