Probing Molecular Mechanisms during the Oscillatory Adsorption of Propyl Chain Functionalized Organosilane Films with Sum Frequency Generation Spectroscopy

Ruby A. Sims, Hidenori Noguchi, Sarah L. Harmer, Jamie S. Quinton, Kohei Uosaki

Research output: Contribution to journalArticlepeer-review

Abstract

The selectivity rules of sum frequency generation spectroscopy were exploited to determine propyl chain order during the time-dependent oscillatory adsorption of propyltrimethoxysilane (PTMS) and Langmuir-type growth of propyldimethylmethoxysilane (PDMMS). During the early stages of film growth, molecular packing density determines the extent of propyl chain defects within both films with high surface coverage resulting in a film with fewer defects. Following this, an ordered monolayer-like film stabilizes on the Al2O3 substrate for both silanes. Although this result is intuitive for the Langmuir-type growth of PDMMS, the stabilization of molecular ordering despite the continuing oscillation in PTMS surface coverage indicates the presence of a stable monolayer, while it is the oligomerized PTMS dendrimers which continue to desorb and readsorb to the substrate. We also reveal for the first time, the formation of a physisorbed bilayer during the self-assembly process of PTMS. The presence of this ordered, physisorbed bilayer on top of the covalently bound PTMS film plays a key role in the process of the molecular self-assembly mechanism and is proposed to enable further condensation of the covalently bound film.

Original languageEnglish
Pages (from-to)4383-4392
Number of pages10
JournalJournal of Physical Chemistry B
Volume125
Issue number17
Early online date16 Feb 2021
DOIs
Publication statusPublished - 6 May 2021

Keywords

  • Thin films
  • Group 14 compounds
  • Nonlinear optics
  • Inorganic compounds
  • Molecules
  • National Institute for Materials Science (NIMS)
  • Flinders Microscopy and Microanalysis (FMMA)
  • South Australian Regional Facility (SARF)
  • Microscopy Australia (MA)

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