There is a general assumption, albeit challengeable, that the interfacial properties of self-assembled monolayers (SAMs) are well understood— the premise on which many studies/technologies are based. Due to a large volume of work in SAMs, it has been largely assumed that their wetting (a fundamentally informative property) and related properties are well understood, for example the so-called odd-even effect. Through carefuly studies, this talk demonstrates that there exists complimentary limits in substrate surface roughness where either the molecule or capillary forces (or substrate's surface morphology) dominates the surface properties of a functionalized surface. By fabricating surfaces with root-mean-square roughness of 0.18 nm – 3.4 nm, and surveying wetting of probe liquids across a range of surface tensions on n-alkanethiolate SAMs (C10-C16), we observe that a transition occurs at ~1-1.5 nm. We summarize the data in a so-called ‘Scarlett quadrangle’ that can be used to predict the dominant factor in the study of liquid-SAM interactions. We extend this study to charge transport and engineer the nature of a liquid-metal SAM interface to enhance the contact and hence promote better charge injection into the SAM. A discussion on the effect of engineering the nature of contact in understanding the effect of interfacial vs bulk properties of the SAM on charge transport through large area junctions of the type M-SAM//liquid-metal (EGaIn) will be presented.

What is in a contact? Understanding basic interfacial properties of self-assembled monolayers by engineering substrate roughness

251st National Meeting (2016)

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