title: 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 CH3from 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 SAMEand SAMOfabricated 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 CH3group have a chain-length dependence. There seems to be a transition at around C13, beyond which SAMs become "solid-like".
authors.affiliation: Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA. mthuo@iastate.edu and Microelectronic Research Centre, Iowa State University, Ames, IA 50011, USA.
authors.forename: Jiahao
authors.initials: J
authors.lastname: Chen
authors.affiliation: Department of Chemistry and the Photonics Centre, Boston University, Boston, MA 02215, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA. mthuo@iastate.edu.
authors.forename: Ian D
authors.initials: ID
authors.lastname: Tevis
authors.affiliation: Department of Chemistry and the Photonics Centre, Boston University, Boston, MA 02215, USA.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Andino
authors.affiliation: Department of Chemistry and the Photonics Centre, Boston University, Boston, MA 02215, USA.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Miller
authors.affiliation: Department of Chemistry and the Photonics Centre, Boston University, Boston, MA 02215, USA.
authors.forename: Lawrence D
authors.initials: LD
authors.lastname: Ziegler
authors.affiliation: Department of Chemistry and the Photonics Centre, Boston University, Boston, MA 02215, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA. mthuo@iastate.edu and Microelectronic Research Centre, Iowa State University, Ames, IA 50011, USA.
authors.forename: Martin M
authors.identifier: http://orcid.org/0000-0003-3448-8027
authors.initials: MM
authors.lastname: Thuo