Epitaxial transfer through end-group coordination modulates the odd–even effect in an alkanethiol monolayer assembly

Abstract

Short spacer length and high end-group coordination lead to the top network acting as a template for the buried sulfur–gold interface of n-alkanethiols (SH–(CH₂)_n–OH or SH–(CH₂)_n–CH₃) on gold {111}. Annealing and templating both drive toward a higher sampling of the spatially favorable bridge adsorption sites. The hydrogen-bonded network increases in strength by increasing the number of hydrogens participating per oxygen, from 1.75 to 1.98 for n = 14–30. Higher n leads to better packing (five times for hydroxyl-terminated and seven times for methyl-terminated for n = 14–30) and stability of monolayers, while lower n results in better epitaxial transfer (transfer coefficient ratio = 13.5 for {SH–(CH₂)₁₄–OH}/{SH–(CH₂)₃₀–CH₃}) and actuation. Odd values of n for the hydroxyl-terminated n-alkanethiols lead to lattice spacing of an average of 0.04 ± 0.01 Å higher than even values. There is a structural transition in properties around spacer length n = 24–27. Characterization of monolayer assembly through correlation between adatom and network layers provides recursive design principles for actuation and sensing applications.