- Title
- Combined STM, AFM and DFT study of the HOPG / 1-octyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)amide ([OMIm]Tf2N) interface
- Creator
- Carstens, Timo; Gustus, René; Höfft, Oliver; Borisenko, Natalia; Endres, Frank; Li, Hua; Wood, Ross J.; Page, Alister; Atkin, Rob
- Relation
- Journal of Physical Chemistry: C Vol. 118, Issue 20, p. 10833-10843
- Publisher Link
- http://dx.doi.org/10.1021/jp501260t
- Publisher
- American Chemical Society
- Resource Type
- journal article
- Date
- 2014
- Description
- The highly ordered pyrolytic graphite (HOPG) / 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([OMIm]Tf2N) interface is examined by ultrahigh vacuum scanning tunneling microscopy (UHV-STM) and atomic force microscopy (UHV-AFM), and as a function of potential by in situ scanning tunneling microscopy (STM), in situ atomic force microscopy (AFM) and density functional theory (DFT) calculations. In situ STM and AFM results reveal that multiple ionic liquid (IL) layers are present at the HOPG / electrode interface at all potentials. At open circuit potential (OCP), attractions between the cation alkyl chain and the HOPG surface result in the ion layer bound to the surface being cation rich. As the potential is varied, the relative concentrations of cations and anions in the surface layer change: as the potential is made more positive anions are preferentially adsorbed at the surface, while at negative potentials the surface layer is cation rich. At -2 V an unusual overstructure forms. STM images and AFM friction force microscopy measurements both confirm that the roughness of this overstructure increases with time. DFT calculations reveal that [OMIm]+ is attracted to the graphite surface at OCP, but adsorption is enhanced at negative potentials due to favorable electrostatic interactions, and at -2 V the surface layer is cation rich and strongly bound. The energetically most favorable orientation within this layer is with the [OMIm]+ octyl chains aligned “epitaxially” along the graphitic lattice. This induces quasi-crystallization of cations on the graphite surface and formation of the overstructure. An alternative explanation may be that, because of the bulkiness of the cation sitting along the surface, a single layer of cations is unable to quench the surface potential, so a second layer forms. The most energetically favourable way to do this might be in a quasi-crystalline / multilayered fashion. It could also be a combination of strong surface binding / orientations and the need for multilayers to quench the charge.
- Subject
- ionic liquid; gold; potential; STM; AFM; DFTB
- Identifier
- http://hdl.handle.net/1959.13/1046704
- Identifier
- uon:14672
- Identifier
- ISSN:1932-7447
- Rights
- This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Physical Chemistry © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp501260t
- Language
- eng
- Full Text
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