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Quantification of fluorine density in the outermost atomic layer
R D van de Grampel1, W Ming, A Gildenpfennig
1Laboratory of Coatings Technology, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands.
Langmuir : the ACS Journal of Surfaces and Colloids
|March 5, 2005
Summary
Low-energy ion scattering quantified fluorine density in perfluorinated thiol monolayers on gold and poly(tetrafluoroethylene) (PTFE). Differences in fluorine density were attributed to varying molecular tilt angles, providing insights into surface chemistry.
Area of Science:
- Surface science
- Materials science
- Analytical chemistry
Background:
- Perfluorinated thiol monolayers are crucial for modifying surface properties.
- Understanding the atomic structure of these monolayers is essential for their application.
- Poly(tetrafluoroethylene) (PTFE) is a widely used fluoropolymer with unique surface characteristics.
Purpose of the Study:
- To analyze the outermost atomic layer of perfluorinated thiol monolayers on gold and PTFE.
- To achieve absolute quantification of fluorine density in these monolayers.
- To provide configurational and molecular interpretations of the monolayer structure on gold.
Main Methods:
- Low-energy ion scattering (LEIS) was employed for surface analysis.
- A calibration standard, LiF(100) single crystal, was used for accurate fluorine signal quantification.
- Comparative analysis was performed on perfluorinated thiol monolayers on gold and PTFE surfaces.
Main Results:
- Absolute fluorine densities were determined for monolayers on gold (1.48 x 10^15 F atoms/cm^2) and PTFE (1.24 x 10^15 F atoms/cm^2).
- The observed differences in fluorine density were correlated with varying tilt angles of the molecules relative to the surface normal.
- Configurational and molecular models were developed to explain the structure of the perfluorinated thiol monolayer on gold.
Conclusions:
- LEIS is a powerful technique for quantifying fluorine density in ultrathin organic films.
- Molecular orientation significantly influences the surface fluorine density of perfluorinated monolayers.
- The study provides a detailed understanding of perfluorinated thiol monolayer structures on different substrates.