Order and Melting in Self-Assembled Alkanol Monolayers on Amorphous SiO2

Julia Haddad, Hans Georg Steinrück, Htay Hlaing, Sumit Kewalramani, Diego Pontoni, Harald Reichert, Bridget M. Murphy, Sven Festersen, Benjamin Runge, Olaf M. Magnussen, Andreas Magerl, Moshe Deutsch, Benjamin M. Ocko*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Molecular self-assembly is a key to wide-ranging nano- and microscale applications in numerous fields. Understanding its underlying molecular level science is therefore of prime importance. This study resolves the Å-scale structure of the earliest and simplest self-assembled monolayer (SAM), octadecanol on amorphous-SiO2-terminated Si(001) substrate, and determines the structure's temperature evolution. At low temperatures lateral hexagonal order exists, with close-packed, surface-normal molecules. At ∼12 °C above the alkanol's bulk melting, a fully reversible disordering transition occurs to a novel "stretched liquid" phase, laterally disordered, but only ∼15% thinner SAM than in the crystalline phase. The SAM persists to ≥100 °C. A thermodynamic model yields here a headgroup-substrate bond energy ∼40% lower than on crystalline sapphire, highlighting the importance of the substrate's order, and near-epitaxy, for the SAM's ordering and stability.

Original languageEnglish (US)
Pages (from-to)17648-17654
Number of pages7
JournalJournal of Physical Chemistry C
Volume119
Issue number31
DOIs
StatePublished - Aug 6 2015

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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