Alkyne-functionalized cyclooctyne on Si(001) – reactivity studies and surface bonding from an energy decomposition analysis perspective

<p>The reactivity and bonding of an ethinyl-functionalized cyclooctyne on Si(001) is studied by means of density functional theory. This system is promising for the organic functionalization of semiconductors. Singly bonded adsorption structures are obtained by [2+2] cycloaddition reactions of the cyclooctyne or ethinyl group with the Si(001) surface. A thermodynamic preference for an adsorption with the cyclooctyne group in on-top position is found and traced back to minimal structural deformation of adsorbate and surface with the help of the energy decomposition analysis for extended systems (pEDA). Starting from singly bonded structures a plethora of reaction paths describing conformer changes and consecutive reactions with the surface are discussed. Strongly exothermic and exergonic reactions to doubly bonded structures are presented, while small reaction barriers highlight the high reactivity of the studied organic molecule on the Si(001) surface. Dynamic aspects of the competitive bonding of the functional groups are addressed by ab initio molecular dynamics calculations. Several trajectories to doubly bonded structures are obtained in agreement to calculations using the nudged-elastic band approach. However, our findings are in disagreement with experimental observations of a selective adsorption by the cyclooctyne moiety, which is critically discussed.</p>