Fabrication et étude d'une diode moléculaire à résistance
différentielle négative greffée sur silicium terminé hydrogène.

Abstract : Molecular electronics aims at the use of the transport of electrons through the frontier orbitals of a single molecule or a small group of molecules. Its development implies the achievement of hybrid devices where molecular components stand alongside classical CMOS components. This work aims at the manufacturing of such a device. In this project, a complex molecular monolayer constitutes the electroactive core of a vertical device. The bottom electrode is the silicon substrate to which the monolayer is covalently grafted. The top electrode is made of a single wall carbon nanotube. This ready-made nanometric electrode limits the number of connected molecules. It is then connected to gold leads build by a classical top-down process.
The first part of this work focused on the multisteps synthesis of complex molecular monolayers grafted on hydrogen terminated silicon surfaces. This is a three steps process. First we prepared atomically flat Si(111)-H substrate by anisotropic wet etching. Then we grafted a simple aliphatic monolayer terminated by a functional group. Finally we used this simple monolayer as precursor for the synthesis of the target complex monolayer through simple and mild chemical reactions. This multisteps approach avoid to expose the whole final molecule to the grafting step conditions. Two grafting methods were used : thermal hydrosilylation of w-functionalised 1-alkenes and electrochemical cleavage of halogenoalkanes. One of the main result is the monolayer packing achieved depending of the steric hindrance of the functional group for the simple monolayer. Finally we used the reactivity of carboxyl and N-succinimidyl ester terminated monolayers to build target monolayers through esterification or amidification reactions. All along the process, surfaces were characterised using ATR-FTIR, XPS and AFM. A peculiar attention was paid to the reoxidation of the silicon substrate.
In the second part of this work, we focused on the manufacturing by classical top-down means of an electronic device that could interface the molecular monolayer grafted on silicon to microscopic leads. This device is based on a double trench etched in a thick silicon oxide layer. This is an attempt to address an intrinsic difficulty of the molecular electronics : on one hand the SWNT must come in contact with the few nanometers thin monolayer, on the other hand, the gold/SWNT must be done on an oxide layer thick enough to avoid leakage current. Although this device did not allow electrical measurement of the transport properties of a monolayer, it is still a first step toward integration of molecular electronics in a CMOS architecture.
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Laurent Baraton. Fabrication et étude d'une diode moléculaire à résistance
différentielle négative greffée sur silicium terminé hydrogène.. Matériaux. Université Paris Sud - Paris XI, 2004. Français. ⟨tel-00150238⟩

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