Louis Porte

Organized Formation of 2D Extended Covalent Organic Frameworks at Surfaces

The development of nanoscale masking for particle deposition is exceedingly important to push the future of nanoelectronics beyond the current limits of lithography. We present the first example of ordered hexagonal covalent nanoporous structures deposited in extended arrays of near monolayer coverage across a Ag(111) surface. The networks were formed from the deposition of the reagents from a heated molybdenum crucible between 370 and 460 K under ultrahigh vacuum (UHV) onto a cleaned Ag(111) substrate and imaged using a scanning tunneling microscope (STM). Two surface covalent organic frameworks (SCOFs) are presented; the first is formed from the deposition of 1,4-benzenediboronic acid (BDBA) and its dehydration to form the boroxine-linked SCOF-1, the second is formed from the co-deposition of BDBA and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) to form a dioxaborole-linked SCOF-2 network. The networks were found to produce nanoporous structures of 15 A for SCOF-1 and 29 A for SCOF-2, which agreed with theoretical pore sizes determined from DFT calculations. Both SCOFs were found to have exceptional thermal stability, maintaining their structure until approximately 750 K, which was found to be the polymer degradation temperature from thermal gravimetric analysis (TGA).

Single Layer of Polymeric Fe-Phthalocyanine: An Organometallic Sheet on Metal and Thin Insulating Film

Supramolecular chemistry on a surface has produced a large variety of atomically controlled systems, but practical applications are seriously restricted by the use of weakly cohesive non-covalent bonds and by the confinement to a metal surface. Here we report on the formation of a well-ordered organometallic sheet consisting of two-dimensional polymeric phthalocyanine. Remarkably, the growth demonstrated on a metal surface can be extended onto a thin insulating film. We thus expect the intrinsic properties to be preserved, and the system should be easily transferable to real devices.

Tip- or electron beam-induced surface polymerization

Control on the formation of a two-dimensional polymer could be achieved in two different ways. Manipulation with the tip of a scanning tunneling microscope allowed for assigning the localization of the polymerization reaction. Additionally, electron irradiation could accelerate greatly the reaction kinetics.

Robust Supramolecular Network on Ag(111): Hydrogen-Bond Enhancement through Partial Alcohol Dehydrogenation

Alcohol oxidation and self-assembly: the in situ oxidation of hydroxyl functional groups to quinone groups promotes the formation of enhanced hydrogen bonds and allows reorganization of the resulting supramolecular self-assemblies, which evolve from a weakly bound dense phase to a strongly bound nanoporous open structure (see picture).

Side functionalization of diboronic acid precursors for covalent organic frameworks

A series of substituted 1,4-benzenediboronic acids (BDBA) was synthesized and their thermal properties investigated. Two diboronic acids were studied as building-blocks for covalent organic framework (COF) formation, namely 2,5-dimethoxy-1,4-benzenediboronic acid and 2-nitro-1,4-benzeneboronic acid. Interestingly, substitution of the BDBA core caused a dramatic decrease of the polymerization temperature leading to the formation of a less organized structure.

Two‐Dimensional Polymer as a Mask for Surface Nanopatterning

NaCl islands are used as a sacrificial layer to selectively deposit a boronic acid based two-dimensional polymer. The nanostructured polymer layer can be used as a negative mask to create Fe islands in a nanolithography mimicking process.

Solvent induced aggregation of protoporphyrin and octacarboxylphthalocyanine of zinc deposited on gold surface

In this paper, we studied the influence of solvent on the morphology of zinc protoporphyrin and zinc octacarboxylphthalocyanine films transferred onto gold surface by dipping. In these films, carboxylic acid groups borne in periphery of macrocycles allow anchoring to gold via ionic interaction. First, we followed by UV-Visible absorption spectroscopy the solvation state of these conjugated macrocycles in pure DMF, in pure ethanol and in various ethanol/DMF mixtures. We show that the increase in ethanol proportion promotes interactions between macrocycles. Second, molecular layers of macrocycles spontaneously adsorbed from these various solutions onto gold surface were analyzed by ellipsometry, water contact angle measurements, UV-Visible absorption spectroscopy and atomic force microscopy. Results evidenced the layers were mainly composed of grains whose size of a few nanometers was directly related to the solvation conditions of molecules. In addition, Q band splitting was observed in the absorption spectrum of zinc octacarboxylphthalocyanine grain films which indicates specific organization of those molecules. Therefore solvent is shown to have a profound influence on the nanostructuration of as-prepared macrocycle layers on gold surface by promoting pre-organization in solution, and its composition enables to better control the morphology of those films by tuning the solubilization of macrocycles.

Structure and growth mechanism of self-assembled monolayers of metal protoporphyrins and octacarboxylphthalocyanine on silicon dioxide

In this work, we studied the structure and the growth of various conjugated macrocyclic SAMs (two protoporphyrins ZnPP and FePP, and one phthalocyanine ZnPc(COOH)8) on silicon dioxide previously functionalized by aminopropyltrimethoxysilane (APTMS) for covalent grafting of macrocycles on the surface. The samples were characterized by atomic force microscopy (AFM), ellipsometry, contact angle measurements, Fourier transform infrared (FTIR) and UV-visible spectroscopy. A growth model of macrocycle layers in three steps was established from ellipsometry and UV-visible results at various deposition times. Firstly, a fast adsorption of macrocycles occurs on the surface in a disordered way followed by a rearrangement phase. Then, the layers get denser by adsorption of supplementary macrocycles on the surface. Spectroscopic and morphological analyses reveal a specific structure for each deposited macrocycle. The size of the macrocycle core and nature of the metallic atom are shown to be key factors which govern orientation and assembly of macromolecules on the surface. Finally, the essential issue of film stability in an ambient atmosphere has been addressed.