| AVS 65th International Symposium & Exhibition | |
| Surface Science Division | Thursday Sessions |
| Session SS+AS+BI+MI+NS-ThA |
| Session: | Organic/Inorganic Surfaces, Interfaces and Nanostructures |
| Presenter: | Renjie Liu, Lakehead University, Canada |
| Authors: | R. Liu, Lakehead University, Canada C. Fu, McGill University, Canada A.G. Moisseev, McGill University, Canada M.R. Rao, McGill University, Canada Y. Chen, McGill University, Canada D.F. Perepichka, McGill University, Canada M.C. Gallagher, Lakehead University, Canada |
| Correspondent: | Click to Email |
Given potential applications in molecular electronics, organic thin films continue to attract a great deal of scientific attention. Furthermore, organic-inorganic semiconductor hybrids have been identified as a possible platform for future devices. Generally such a device would require thin films of functionalized organic molecules grown on silicon surfaces. To promote the growth of high quality films, the Si surface needs to be passivated. For example, the Si(111) √3×√3-Ag surface has been shown to be weakly interacting, allowing molecules to remain mobile and form well ordered layers [1].
In this work we compare the adsorption and self-assembly of two halogenated molecules of threefold symmetry; 2,4,6-tris(4-iodophenyl)-1,3,5-triazine (TIPT), and tribromotrioxaazatriangulene (TBTANG) on the Si(111)-√3×√3-Ag surface. The self assembly of TIPT on HOPG and Au(111) has been reported previously [2], and heteroatom forms of triangulene are of particular interest in molecular electronics [3].
We find that both molecules display high mobility on the √3-Ag surface. With increasing molecular dose, TIPT forms supramolecular domains defined by a 2.0 nm by 1.8 nm rectangular cell. The size and symmetry of the unit cell provides strong evidence that a large fraction of the monomers do not undergo de-halogenation, and that the dominant interaction within the domains is intermolecular I···H hydrogen-bonding. As the coverage approaches one monolayer, the film consists of supramolecular domains of limited extent separated by regions of disorder. STM images at lower coverage reveal that molecular adsorption increases the defect density of the underlying √3-Ag layer. We believe that a small fraction of the TIPT molecules de-iodinate on adsorption and that the iodine subsequently reacts with the Ag overlayer. The increased defect density limits the extent of the supramolecular domains on this surface.
In contrast, TBTANG exhibits long-range self-assembly of intact molecules. The ordered structure is characterized by several closely packed rows of molecules. Within the rows the repeating motif is two-molecules linked together by Br···Br interactions. With increasing coverage, the √3 surface remains unaffected and the self assembled layer extends over the entire surface.
[1] Yokoyama, T. et al., J Chem Phys 142, 204701 (2015).
[2] Gatti, R. et al., J. Phys. Chem. C 118, 25505–25516 (2014).
[3] Nakatsuka, S. et al., Angewandte Chemie 129, 5169–5172 (2017).