Etude de monocouches de molécules organiques par spectroscopie de génération de fréquence-somme simplement et doublement résonnante et par spectroscopie de diffusion Raman anti-Stokes cohérente

Abstract

This research aims at studying organic molecule monolayers by nonlinear optical spectroscopies, in order to characterize their structure, their order, and their vibrational properties specific to the interface. Singly resonant sum-frequency generation (SFG) is a nonlinear, optical, vibrational spectroscopy. Using SFG, it is possible to deduce the organization of molecular interfaces . We investigated the interface structure of self-assembled monolayers (SAM) produced by two different methods: one acts in the liquid phase and the other operates in the gas phase in ambient pressure conditions. Both methods produced well-organized interfaces after long preparation times but gas-phase adsorption produces high-quality monolayers much faster than deposition from the liquid phase. The vibrational and electronic structures of the alkali-doped (with K and Cs) C60/metal interfaces are coupled. This coupling determines fundamental properties of the fullerenes, including their (super-) conductivity. Using doubly resonant SFG, we showed the occurrence of interface electron-phonon couplings involving the pentagonal pinch mode of C60. These couplings have an extramolecular and an intramolecular origin, that are responsible for the infrared and resonant- Raman activities of the Ag(2) mode, respectively. We identified the energy and the nature of the electronic transition responsible for the DR-SFG process. In addition, we adapted the DR-SFG spectrometer available in our laboratory to use it as a coherent anti-Stokes Raman spectrometer, in order to analyze the nonlinear optical properties of interfaces in a large vibrational frequency range. To demonstrate the operation of the CARS spectrometer, we first characterized mineral surfaces of the apatite kind. Then we studied C60 layers deposited on Au(111) and Si(100).

Date of Award	26 Aug 2010
Original language	French
Awarding Institution	University of Namur
Supervisor	Yves Caudano (Supervisor), Paul THIRY (Co-Supervisor), Andre Peremans (Jury), Benoit Champagne (Jury), Zineb Mekhalif (President) & Abderrahmane Tadjeddine (Jury)