Abstract
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 adsorption with the cyclooctyne group in the on-top position is found and traced back to minimal structural deformation of the adsorbate and surface with the help of 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 for the doubly bonded structures are obtained in agreement with calculations using the nudged elastic band approach. However, our findings disagree with the experimental observations of selective adsorption by the cyclooctyne moiety, which is critically discussed.
Highlights
Received: 30 September 2021Accepted: 27 October 2021Published: 2 November 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Silicon is already the most intensively used element for semiconductor devices [1]
Further development of applications in the field of solar cells, organic light emitting diodes (OLED) or molecular electronics emerge if the silicon surface is combined with organic molecules [2,3,4,5,6,7,8]
While our findings suggest that ECCO should bind to the Si surface with both functional groups whenever possible, the experimental results [41] support selective adsorption by the cyclooctyne group without consecutive reactions
Summary
Received: 30 September 2021Accepted: 27 October 2021Published: 2 November 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Silicon is already the most intensively used element for semiconductor devices [1]. Well-ordered organic layers are required to ensure proper device functionality [7,8,9,10]. This is a challenging task since the silicon surface exhibits a high reactivity toward organic molecules [11,12,13,14]. To address this challenge, bifunctional organic molecules are investigated. The idea is to design an organic molecule which is suited to selectively react (Figure 1) with the silicon surface. Selectivity means that one functional group is reacting way faster with the silicon surface than the second functional group [15,16,17,18]
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