Diacetylene polymerization on a bulk insulator surface

Abstract

Molecular electronics has great potential to surpass known limitations in conventional silicon-based technologies. The development of molecular electronics devices requires reliable strategies for connecting functional molecules by wire-like structures. To this end, diacetylene polymerization has been discussed as a very promising approach for contacting single molecules with a conductive polymer chain. A major challenge for future device fabrication is transferring this method to bulk insulator surfaces, which are mandatory to decouple the electronic structure of the functional molecules from the support surface.Here, we provide experimental evidence for diacetylene polymerization of 3,3 0 -(1,3-butadiyne-1,4-diyl)bisbenzoic acid precursors on the (10.4) surface of calcite, a bulk insulator with a band gap of around 6 eV. When deposited on the surface held at room temperature, ordered islands with a (1 Â 3) superstructure are observed using dynamic atomic force microscopy. A distinct change is revealed upon heating the substrate to 485 K. After heating, molecular stripes with a characteristic inner structure are formed that excellently match the expected diacetylene polymer chains in appearance and repeat distance. The corresponding density functional theory computations reveal molecular-level bonding patterns of both the (1 Â 3) superstructure and the formed striped structure, confirming the assignment of on-surface diacetylene polymerization. Transferring the concept of using diacetylene polymerization for creating conductive connections to bulk insulator surfaces paves the way towards application-relevant systems for future molecular electronic devices.

Micrometre-long covalent organic fibres by photoinitiated chain-growth radical polymerization on an alkali-halide surface

“…35,36 Furthermore, it was shown that for electronic devices with predominant lateral transport the spacer layers must have a thickness of at least 3-4 monolayers (ML) 35 and when permanent charging of single molecules is desired, the layer must be even thicker. 39 On bulk insulating substrates, successful polymerization was so far obtained on calcite 40,41,42,43,44 and mica 45 surfaces which have a high surface energy 46 and provide a strong anchoring of the molecules to the substrates which allows for relatively large annealing temperatures (500K). 42 UV-induced polymerization on bulk insulators was demonstrated for pre-arranged supramolecular structures for both 1D 44 and 2D structures.…”

“…39 On bulk insulating substrates, successful polymerization was so far obtained on calcite 40,41,42,43,44 and mica 45 surfaces which have a high surface energy 46 and provide a strong anchoring of the molecules to the substrates which allows for relatively large annealing temperatures (500K). 42 UV-induced polymerization on bulk insulators was demonstrated for pre-arranged supramolecular structures for both 1D 44 and 2D structures. 42 (ii) The so far largest, defect-free organic layers have been achieved by supramolecular selfassembly (SA) in which the molecule-molecule (MM) interaction is dominated by relatively weak and reversible Van der Waals (VdW) or Hydrogen bonding.…”

“…The highly ordered and long nanofibres are formed owing to: the fact that the UV-induced radical polymerization is chain-like, that it is guided by the molecule-substrate interaction, and that the reaction takes place in a diluted 2D gas phase acting as a reservoir of the precursor molecules that allows unhindered propagation, rather than through pre-arranged structures, as has previously been shown on insulating surfaces. [40][41][42][43][44] In addition, photo-induced polymerization does not require thermal annealing (by opposition with catalytic on-surfaces reactions) which is a major advantage in order to avoid the formation of defects during the polymerisation. The conclusions on the polymerization process are supported by Density Functional Theory (DFT) and Climbing Image Nudged Elastic Band (NEB) calculations, and the structure and stability of the covalent micrometer-long organic fibres are verified experimentally by noncontact Atomic Force Microscopy (ncAFM).…”

Homocoupling of terminal alkynes on calcite (10.4)

“…Additionally, the molecule is also equipped with two carboxylic acid functionalities, which have previously proven to act as suitable anchors on the calcite (10.4) surface and prevent the desorption at elevated temperatures. Density-functional theory calculations have suggested an interaction of the carbonyl groups with the calcium ions via electrostatics, while the hydroxyl groups form hydrogen bonds with the calcite carbonate group oxygen atoms [23,24] . Furthermore, a detailed investigation towards a possible deprotonation has been performed, suggesting a transition of the hydrogen from the hydroxyl group towards the oxygen of the carbonate group under formation of a hydrogen bond [23,24] .…”

“…Density-functional theory calculations have suggested an interaction of the carbonyl groups with the calcium ions via electrostatics, while the hydroxyl groups form hydrogen bonds with the calcite carbonate group oxygen atoms [23,24] . Furthermore, a detailed investigation towards a possible deprotonation has been performed, suggesting a transition of the hydrogen from the hydroxyl group towards the oxygen of the carbonate group under formation of a hydrogen bond [23,24] . Two anchor groups were chosen here for symmetry reasons and to also promote molecule-molecule interactions that can be beneficial for the formation of an ordered selfassembled structure as compared to mobile species.…”