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Séminaire général de l’INSP

Hierarchical engineering of 2D self-assembled porous organic-based nanoarchitectures on metal surfaces : on-surface synthesis of porous organic covalent-structures and self-assembled hybrid organic-ionic architectures - Fabien Silly - Jeudi 24 mai 2018 à 16 h 30

INSP - Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 22-23, 3e étage, salle 317

Fabien Silly - TITANS, SPEC, CEA Saclay, CNRS, Université Paris-Saclay

Abstract

Engineering novel atomic and molecular nanostructures on surfaces is a challenge in nanosciences. We develop new process to engineer novel two-dimensional porous nanorachitectures based on molecular self-assembly on surfaces. PTCDI molecule self-assembled into compact domains on metal surfaces. We show that novel porous hybrid nanoarchitectures can bee engineered by mixing this molecule with ionic compounds. We fabricated three two-dimensional self-assembled hybrid PTCDI–NaCl nanoarchitectures, i.e. a flower-structure, a mesh-structure and a chain-structure on Au(111), Fig.1. Scanning tunneling microscopy (STM) reveals that NaCl-dimers selectively interact with molecular N–H groups. The PTCDI∙∙∙NaCl-dimer binding appears to be highly directional.

Alternatively engineering two-dimensional (2D) covalent carbon-based nanoarchitectures has received tremendous attention during the resent years. We investigate on-surface bottom-up synthesis to create patterned graphene nanoarchitectures via Ullmann coupling. Star-shaped 1,3,5-Tris(4-iodophenyl)benzene molecules (Fig.2) self-assemble into halogen-bonded structures on graphite [2]. In contrast, our STM measurements reveal that on-surface synthesis of covalent nanoarchitectures is competing with the growth of self-assembled halogen-bonded structures when this molecule is deposited on Au(111) in vacuum [3], Fig.2. We show that the molecules form covalent polygonal nanoachitectures at the gold surface step edges and at the elbows of the gold reconstruction at low coverage. With coverage increasing two-dimensional halogen-bonded structures appear and grow on the surface terraces. At high coverage the competitive growth between the covalent and halogen-bonded nanoarchitectures leads to formation of a two-layer film above one monolayer deposition. For this coverage, the covalent nanoarchitectures are propelled on top of the halogen-bonded first layer.

We then investigated the on-surface synthesis of covalent nanoarchitectures of star-shaped 1,3,5-tris(3,5-dibromophenyl)-benzene molecules on Au(111). This molecule has two bromine atoms at the extremity of each arm. At room temperature, the molecules self-assemble into a porous halogen-bonded network [4,5]. One-covalent-bond dimers appear on the surface after annealing at 145 °C. One-covalent-bond chains are created after annealing at 170 °C. One-covalent-bond hexagons as well as two-covalent-bond dimers are appearing on the surface after annealing at 175 °C. Annealing at 275 °C leads to the formation of a porous 2D hexagonal two-covalent-bond nanoarchitecture. STM images show that the number of intermolecular covalent bonds increases as the temperature rises.

References : 1) J. Hieulle, D. Peyrot, Z. Jiang, F. Silly, Chem. Commun. 51, 13162 (2015)
2) F. Silly, J. Phys. Chem. C 117, 20244 (2013)
3) D. Peyrot, F. Silly, ACS Nano 10, 5490-5498 (2016)
4) D. Peyrot, M. G. Silly, F. Silly, Phys. Chem. Chem. Phys. 20, 3918-3924 (2018)
5) D. Peyrot, M. G. Silly, F. Silly, J. Phys. Chem. C 121, 26815-26821 (2017)