Formation of carboxy- and amide-terminated alkyl monolayers on silicon(111) investigated by ATR-FTIR, XPS, and X-ray scattering: Construction of photoswitchable surfaces

Karola Rück-Braun, Michael Åxman Petersen, Fabian Michalik, Andreas Hebert, Daniel Przyrembel, Christopher Weber, Saleh A. Ahmed, Stefan Kowarik, Martin Weinelt

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

We have prepared high-quality, densely packed, self-assembled monolayers (SAMs) of carboxy-terminated alkyl chains on Si(111). The samples were made by thermal grafting of methyl undec-10-enoate under an inert atmosphere and subsequent cleavage of the ester functionality to disclose the carboxylic acid end-group. X-ray photoelectron spectroscopy (XPS) and grazing incidence X-ray diffraction (GIXD) indicate a surface coverage of about 50% of the initially H-terminated sites. In agreement, GIXD implies a rectangular unit mesh of 6.65 and 7.68 Å side lengths, containing two molecules in a regular zigzag-like substitution pattern for the ester- and carboxy-terminated monolayer. Hydrolysis of the remaining H-Si(111) bonds at the surface furnished HO-Si(111) groups according to XPS and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) studies. The amide-terminated alkyl SAM on Si(111) assembled in a 2-(6-chloro-1H-benzotriazol-1-yl)-1,1,3,3- tetramethyluronium hexafluorophosphate (HCTU)-mediated one-pot coupling reaction under an inert atmosphere, whereby the active ester forms in situ prior to the reaction with an amino-functionalized photoswitchable fulgimide. ATR-FTIR and XPS studies of the fulgimide samples revealed closely covered amide-terminated SAMs. Reversible photoswitching of the headgroup was read out by applying XPS, ATR-FTIR, and difference absorption spectra in the mid-IR. In XPS, we observed a reversible breathing of the amide/imide C1s and N1s signals of the fulgimide. The results demonstrate the general suitability of HCTU as a reagent for amide couplings to carboxy-terminated alkyl SAMs and the on-chip functionalization toward photoswitchable Si(111) surfaces. © 2013 American Chemical Society.
Original languageEnglish
JournalLangmuir
Volume29
Issue number37
Pages (from-to)11758-11769
ISSN0743-7463
DOIs
Publication statusPublished - 2013

Keywords

  • Amides
  • Esterification
  • Esters
  • Fourier transform infrared spectroscopy
  • Photoelectrons
  • Self assembled monolayers
  • Silicon
  • X ray diffraction
  • X ray photoelectron spectroscopy

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