| AVS 60th International Symposium and Exhibition | |
| Thin Film | Friday Sessions |
| Session TF+EM+NS+SS-FrM |
| Session: | Thin Film: Growth and Characterization III |
| Presenter: | T. Hauffman, Vrije Universiteit Brussel, Belgium |
| Authors: | T. Hauffman, Vrije Universiteit Brussel, Belgium A. Hubin, Vrije Universiteit Brussel, Belgium H.A. Terryn, Vrije Universiteit Brussel, Belgium |
| Correspondent: | Click to Email |
Self-assembling monolayers are one of the most innovative ways to functionalise and change material surface’ properties on the nanoscale. The adsorption of thiols on gold has proven the feasibility to build such well-ordered, compact monomolecular organic structures. However, gold is industrially less relevant and the variety of organic moieties that can be deposited in this way on the noble substrate is very limited.
Therefore, an interesting approach is outlined in literature, involving the deposition of monolayers on oxide films. In particular, the adsorption of phosphonic acids on aluminium oxides is proposed. In this presentation, we address the adsorption of n-octylphosphonic acids from aqueous and ethanolic solutions. It could be proven that not only the adsorbed layer should be characterised, but that the bare sample and the solvent play a crucial role as well. Furthermore, interactions between the oxide, the solvent and the individual molecules should be considered.
In this work, a strong focus laid on the in situ, real time monitoring of the dynamic adsorption of the organic molecules. Therefore, a methodology including in situ AFM, in situ, visual ellipsometry and Odd Random Phase Electrochemical Multisine Impedance Spectroscopy is outlined. Ex situ complementary techniques, such as XPS and FE SEM were included.
As such, it could be proven that in polar solvents, molecules adsorb in a fast and Stranski-Krastanov way. Moving to less polar solvents, such as ethanol, provoke deterioration of the oxide surface. The phosphonic acids adsorb on the surface, giving rise to condensed water on the surface. The acid molecules dissolve in this water, creating a hazardous environment for the oxide film.
In general, we state that it is impossible to form a SAM on aluminium oxide through an acid base elimination condensation reaction using organic molecules that are soluble in water [1-5]. Moreover, conformation and density issues are to be expected when using longer, non water soluble phosphonic acid.
References
1. T. Hauffman, Y. Van Ingelgem, T. Breugelmans, E. Tourwé, H. Terryn, A. Hubin, Electrochemica Acta, accepted for publication.
2. T. Hauffman, A. Hubin, H. Terryn, Surface and Interface Analysis DOI 10.1002/sia.5150.
3. T. Hauffman, T. Breugelmans, Y. Van Ingelgem, E. Tourwé, H. Terryn, A. Hubin, Electrochemistry Communications 22 (2012) 124-127.
4. T. Hauffman, L. Van Lokeren, R. Willem, A. Hubin, H. Terryn, Langmuir 28 (2012) 3167-3173.
5. T. Hauffman, O. Blajiev, J. Snauwaert, C. Van Haesendonck, A. Hubin, H. Terryn, Langmuir 24 (2008) 13450-13456.