Thèse de doctorat en Chimie Physique et Analytique
Sous la direction de François Rochet.
Soutenue en 2012
à Paris 6 .
Etude d'alignement des niveaux d'énergies et de la chimie d'interface des hétérostructures de semi-conducteur de silicium-organique par la spectroscopie de photoélectron X et spectroscopie d'absorption de rayons X par rayonnement synchrotron
To date the most widely used inorganic semiconductor is silicon (Si). There is no denial to its contribution in the current standing of micro-electronics but with time its limitations have been exposed, especially the absence of coupling with opto-electronics due to its indirect band gap. Devices which consist of a hybrid of both organic (e. G. Dyes) and Si are thought to be an interesting extension of the next generation Si-based devices. In this context, the modification of Si with organic molecules represents a promising approach for the incorporation of new functionalities into semiconductors (light harvesting, light emission). This has motivated the current research efforts on organic functionalization of the Si(001) surface, via a reaction of a functional group of the organic molecules with the dimers of the Si (001)– 2×1 surface. However, many interesting molecular objects grafted directly on semiconductor surface are multifunctional, which in most cases leads to competitive reactions with the surface silicon atoms and to multiple adsorption geometries. We have tackled this problem by passivating the silicon surface with cyclopentene (C5H8). The passivated layer has then been used as the substrate to grow molecular layers of TCNQ, (Tetracyanoquinodimethane) and PTCDA (3,4,9,10-perylene tetra carbonyl dianhydride). X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS) have been used to determine the precise adsorption geometry of the buffer layer along with the molecular orientation of the adsorbate. Using the same techniques, the chemical environment of the organic / inorganic heterostructure interface has been studied in detail (PTCDA-cyclopentene / Si(001), TCNQ-cyclopentene / Si(001)) along with the molecular orientation (as function of film thickness) and the variations in band alignment. The latter studies may open new avenues in the development of these heterostructures in which modified silicon surfaces could be used as charge injecting / blocking electrodes.
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