Sequential and Site-Specific On-Surface Synthesis on a Bulk Insulator

Abstract

The bottom-up construction of functional devices from molecular building blocks offers great potential in tailoring materials properties and functionality with utmost control. An important step toward exploiting bottom-up construction for real-life applications is the creation of covalently bonded structures that provide sufficient stability as well as superior charge transport properties over reversibly linked self-assembled structures. On-surface synthesis has emerged as a promising strategy for fabricating stable, covalently bound molecular structure on surfaces. So far, a majority of the structures created by this method have been obtained from a rather simple one-step processing approach. But the on-surface preparation of complex structures will require the possibility to carry out various reaction steps in a sequential manner as done in solution chemistry. Only one example exists in literature in which a hierarchical strategy is followed to enhance structural complexity and reliability on a metallic surface. Future molecular electronic application will, however, require transferring these strategies to nonconducting surfaces. Bulk insulating substrates are known to pose significant challenges to on-surface synthesis due to the absence of a metal catalyst and their low surface energy, frequently resulting in molecule desorption rather than reaction activation. By carefully selecting a suitable precursor molecule, we succeeded in performing a two-step linking reaction on a bulk insulating surface. Besides a firm anchoring toward the substrate surface, the reaction sites and sequential order are encoded in the molecular structure, providing so far unmatched reaction control in on-surface synthesis on a bulk insulating substrate.

On‐Surface Reactions

“…Similarly, the synthesis of poly(3,4‐ethylenedioxythiophene) by polymerization of 2,5‐diiodo‐3,4‐ethylenedioxythiophene on Cu(110) has been shown 16. Further examples for Ullmann‐like on‐surface syntheses have been shown on Cu,17–20 Ag,20–26 Au,19, 26–34 CaCO 3 ,35–37 NaCl@Au,38 h‐BN@Ni,39 sapphire,40 and graphene@Ni 39…”

“…Cu,11, 14–20, 42 Ag,20–26, 42 Au,13, 19, 26–34, 41, 81 CaCO 3 ,35–37 HOPG,42 NaCl@Au,38 h‐BN@Ni39 graphene@Ni39…”

Rasterkraftmikroskopie für die molekulare Strukturaufklärung

“…Die hier gezeigten Beispieles ind a) bordotierte Graphen-Nanobänder mit Sesselkonfiguration auf Au(111), [149] b) chirale Graphen-Nanobänder auf Cu(111) [151] und c) Graphen-Zickzack-Nanobänder auf Au (111). [158,159] Isolierende Substrate erfüllen die wichtige Funktion, da sie die auf ihnen gewachsenen molekularen Strukturen elektronisch entkoppeln und somit interessanten Anwendung zugänglich machen kçnnen. [149].Abdruck von (b) mit Genehmigung von Lit.…”

Mechanisms of Covalent Dimerization on a Bulk Insulating Surface

“…29−31 These achievements have been reviewed in refs 6 and 8, focusing on the relevant experimental and theoretical studies to date, respectively. Despite the considerable progress achieved on metal surfaces, comparatively fewer studies of synthesis on insulating substrates are available in the literature, including reactions on bulk surfaces through Ullmann-type processes, 3,6,19,32 photochemical initiation, 20 and reactions on insulating thin films 18 (see also ref 6 and references therein). Several factors make on-surface syntheses on insulators rather challenging.…”

“…4 More complex molecules resulted instead in zigzag and closed-ring structures by sequential dehalogenations. 19 These architectures were obtained by Ullmann-type or hierarchical sequential linking reactions. However, to the best of our knowledge, there are no theoretical works on the mechanisms of molecular synthesis on insulators providing insights into the hierarchy of possible reaction pathways, although a related work on boron nitride and graphene on Ni(111) was reported.…”