Abstract
Understanding the structural ordering and orientation of interfacial molecular assemblies requires an insight into the penetration depth of the probe molecules which determines the interfacial reactivity. In contrast to the conventional liquid probe-based contact angle measurement in which penetration depth is complicated by the liquid cohesive interaction, we report here a new approach that features a simple combination of vaporous hexane, which involves only van der Waals interaction, and quartz crystal microbalance operated at the third harmonic resonance, which is sensitive to sub-monolayer (0.2%) adsorption. Using this combination, we demonstrated the ability of probing the structural ordering and orientation of the self-assembled monolayers with a sensitivity from penetrating the top portion of the monolayers to interacting with the very top atomic structure at the interface. The determination of the dependence of the adsorption energy of vaporous hexane on the penetration depth in the molecular assembly allowed us to further reveal the atomic-scale origin of the odd-even oscillation, which is also substantiated by density functional theory calculations. The findings have broader implications for designing interfacial reactivities of molecular assemblies with atomic-scale depth precision.
Highlights
Understanding the structural ordering and orientation of molecules on a surface, including atomically- at single crystals and nanoscale-curved surfaces, is key to determining their interfacial functional properties.1a–d This understanding depends on the ability to probe the interface under in situ/ operando conditions, which is complicated o en by the lateral intermolecular interactions of probing molecules, e.g., contact angle and liquid-probe based measurements
The weak van der Waals interaction between vaporous hexane molecule and the monolayer minimizes or eliminates the Scheme 1 An illustration of the simple vaporous probe to terminal region of n-alkanethiolate self-assembled monolayer on gold (111) thin film coated quartz crystal microbalance operated at 3rd harmonic frequency with a detection limit of 0.2% monolayer
We show that the quartz crystal microbalance (QCM) operating at the 3rd harmonic frequency as opposed to the conventional fundamental frequency19b enables the detection of sub-monolayer adsorption of vaporous probe under only van der Waals interactions
Summary
Understanding the structural ordering and orientation of molecules on a surface, including atomically- at single crystals and nanoscale-curved surfaces, is key to determining their interfacial functional properties.1a–d This understanding depends on the ability to probe the interface under in situ/ operando conditions, which is complicated o en by the lateral intermolecular interactions of probing molecules, e.g., contact angle and liquid-probe based measurements.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
