Elie GEAGEA : On-surface chemical reactions studied by STM under UHV

Abstract : This work falls within the framework of the study of chemical reactions on solid surfaces by investigating some cases that have not been studied previously, thereby contributing to the enrichment of knowledge in the field. In this context, the main technique used for the inspection of surface chemical phenomena is scanning tunneling microscopy implemented in an ultra-high vacuum environment.
The first chapter reviews the state-of-the-art by highlighting the basic keys of on-surface chemical reactions through some illustrative works from the literature.
The second chapter presents briefly the theoretical concepts of scanning tunneling microscopy, the experimental setup used to carry out this work, and the various employed surfaces.
The third chapter deals with the subject of elaboration of functional graphene nanoribbons (GNRs) on Cu(111) surface. Thermally-induced reaction of nonhalogenated 9,9’-bianthryl (BA) precursor on Cu(111) surface leads to chiral (3,1)-GNRs. Through our experiments, we revisit the commonly accepted reaction mechanism explaining the growth of (3,1) GNR on a Cu(111) surface while complementing it with an additional intermediate step. Thus, a corollary result based on the completed reactional scheme is proposed using a less reactive surface, Au(111), and the substituted molecules. The latter self-assemble into a 2D supramolecular network which transforms into a coordination polymer via an intramolecular cyclodehydrogenation reaction induced by thermal annealing.
The fourth chapter was motivated by the scarcity of on-surface radical polymerization reactions despite the efficiency of this approach for the fabrication of extended-length polymeric nanowires. The chapter proposes a novel method for obtaining alkyl oligomers in a controlled manner by using on-surface radical oligomerisations triggered by tunneling electrons between the tip of a scanning tunneling microscope and the Si(111)-B surface. We have shown that this electron transfer can ‘switch on’ a sequence leading to the formation of oligomers of defined size distribution due to on-surface confinement of the reactive species.
The fifth chapter focuses on the dissociation of molecular nitrogen N2 as a critical reaction step for the synthesis of value-added products. The chapter proposes a successful N2 dissociation reaction at low pressure and ambient temperature on a Si(111)-7x7 surface. Supported by DFT calculations and XPS experiments, we demonstrate that the low thermal energy collision of the gas molecules with the surface can promote electron transfer to the π* antibonding orbitals of N2 which weaken the N2 bond and leads to its dissociation.
The last chapter summarizes the results of the whole thesis work and presents perspectives for future related work.

Jury Composition :

Frank PALMINO,  University Professor, Université Bourgogne Franche-Comté, PhD Director

Marcus LACKINGER, University Professor, Technical University Munich, Reporter

Uta SCHLICKUM, University Professor, Technische Universität Braunschweig, Reporter

Jérôme LAGOUTE, Research Director, CNRS, Reviewer

Carmelo PIRRI, University Professor, Université de Haute Alsace, Reviewer

Christophe THOMAS, University Professor, Chimie ParisTech, Reviewer

Frédéric CHERIOUX,Research Director, CNRS, PhD Co-Director