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We report surface coverage measurements by Rutherford backscattering spectrometry (RBS) of self-assembled monolayers (SAMs) of both alkyl thiols and oligophenylene thiols on Au-coated mica, Si, and pyrolytic graphite. The 12C atom concentration was probed at 4.266 MeV24He2+ primary beam energy, which enhances the 24He2+ scattering cross section by exciting 12C nuclear resonance states; this is a submode of RBS commonly referred to as nuclear reaction analysis (NRA). The surface coverage of 12C increased linearly with the number of 12C atoms in each SAM. The consistency of the 12C atom coverage values obtained by NRA was cross-checked by measuring the 32S atom concentration by conventional RBS. From these data, we obtained an average coverage of 3.5 ± 0.2 molecules/nm2 for both alkyl thiols and oligophenylene thiols on polycrystalline Au surfaces. The results show the utility of NRA for quantitative analysis of SAM coverage on Au.
Bibliographical noteFunding Information:
This project was supported primarily by NSF under Award CHE-1213876. Partial support came from UMN IPRIME (Industrial Partnership for Research in Interfacial Materials and Engineering). This work was carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program (DMR - 1420013). We thank Dr. Chanmin Su at Bruker Nano for the ultrasharp AFM tips.
© 2016 American Chemical Society.
How much support was provided by MRSEC?
Reporting period for MRSEC
- Period 3
PubMed: MeSH publication types
- Journal Article