Issue 10, 2017

Spectroscopic evidence for the origin of odd–even effects in self-assembled monolayers and effects of substrate roughness

Abstract

This paper reports the effects of substrate roughness on the odd–even effect in n-alkanethiolate self-assembled monolayers (SAMs) probed by vibrational sum frequency generation (SFG) spectroscopy. By fabricating SAMs on surfaces across the so-called odd–even limit, we demonstrate that differentiation of the vibrational frequencies of CH3 from SAMs derived from alkyl thiols with either odd (SAMO) or even (SAME) numbers of carbons depends on the roughness of the substrate on which they are formed. Odd–even oscillation in SFG susceptibility amplitudes was observed for spectra derived from SAME and SAMO fabricated on flat surfaces (RMS roughness = 0.4 nm) but not on rougher surfaces (RMS roughness = 2.38 nm). In addition, we discovered that local chemical environments for the terminal CH3 group have a chain-length dependence. There seems to be a transition at around C13, beyond which SAMs become “solid-like”.

Graphical abstract: Spectroscopic evidence for the origin of odd–even effects in self-assembled monolayers and effects of substrate roughness

Supplementary files

Article information

Article type
Paper
Submitted
07 Nov 2016
Accepted
14 Feb 2017
First published
15 Feb 2017

Phys. Chem. Chem. Phys., 2017,19, 6989-6995

Spectroscopic evidence for the origin of odd–even effects in self-assembled monolayers and effects of substrate roughness

J. Chen, J. Liu, I. D. Tevis, R. S. Andino, C. M. Miller, L. D. Ziegler, X. Chen and M. M. Thuo, Phys. Chem. Chem. Phys., 2017, 19, 6989 DOI: 10.1039/C6CP07580K

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