Bifunctional cyclooctyne molecules on Si(001): Investigating their suitability as interface building blocks using DFT

Pecher, F. Pieck, J.-N. Luy and R. Tonner

Department of Chemistry, Philipps-Universität Marburg, Germany

The creation of organic/semiconductor interfaces is important in extending the application range of semiconductors and in the development of new materials and devices. A possible approach for this is depositing organic molecules onto a silicon surface until the highest possible coverage is reached, and subsequent covalent attachment of further molecules to build up the organic phase layer by layer. Cyclooctyne is a promising candidate for this, as it has been shown to bind strongly to the Si(001) surface and form dense and ordered structures.[1] In order to allow the attachment of the second layer, a functional group has to be introduced at the molecule and furthermore meet the following requirements: Low reactivity and weak interaction with the surface for adsorption selectivity, and easily achievable coupling reactions later on.

We investigate the adsorption dynamics and reactivity of two functionalized cyclooctyne molecules on the Si(001) surface: One featuring an ether side group and another one featuring an ethinyl side group. Since for ethers, reactivity into covalently bound states has been shown to be temperature-controllable,[2,3] the cyclooctyne ether should meet the selectivity requirement, while the ethinyl cyclooctyne promises easily performable click chemistry reactions for the coupling reaction requirement.

Using periodic density functional methods, we present the results for single-molecule adsorption of these two molecules on Si(001). Reaction barriers into the most important bound states are calculated and an estimate of the reactivity at different temperatures is given. Comparing the results, the advantages and disadvantages of using each molecule as an interface building block are furthermore presented and discussed.

[1] G. Mette, M. Dürr, R. Bartholomäus, U. Koert, U. Höfer, Chem. Phys. Lett. 2013, 556, 70.

[2] G. Mette, M. Reutzel, R. Bartholomäus, S. Laref, R. Tonner, M. Dürr, U. Koert, U. Höfer, ChemPhysChem 2014, 15, 3725.

[3] M. Reutzel, G. Mette, P. Stromberger, U. Koert, M. Dürr, U. Höfer, J. Phys. Chem. C 2015, 119, 6018.