%0 Generic
%A AbdElMonem, Ahmed
%D 2008
%F heidok:8586
%K Nichtlinear , optische, Spektroskopie , Grenzfläche , SFGNonlinear , optics, spectroscopy , interfaces , SFG
%R 10.11588/heidok.00008586
%T Nonlinear optical spectroscopy at the Liquid- / Solid- interface
%U https://archiv.ub.uni-heidelberg.de/volltextserver/8586/
%X Sorption-desorption of fatty organic compounds on clay minerals influence the migration process of these compounds in their soil environment, particularly in aquatic medium. In order to understand part of the interaction between such organic compounds and clay minerals, a simple system was considered. Crystalline sapphire was taken as a model for natural clay minerals, and methanol, ethanol, 1-Propanol, 1-butanol, chloroform and propionic acid were chosen as simple but representative model molecules for the more complex organic compounds found in soil. Linear and nonlinear techniques were combined to study the mechanisms of interaction. Sum Frequency Generation (SFG) as a nonlinear interface selective technique was used to probe the adsorption-desorption mechanism at the interfaces for the different systems under study by tracking changes in their average orientation and density at and in vicinity of the surface. Reflectivity in total internal reflection geometry (TIR) was conducted to determine the optical constants of the interface with such high precision that the analysis of the SFG data became feasible, in particular with respect to the determination of molecular orientations. Contact angle and XPS technique were used as inspection tools for the cleanness of the crystal surface. Particular accuracy was required in this work to allow tracking of even subtle changes in the interactions. To achieve such high accuracy, the commercial SFG system applied was further developed and improved to a level of high stability and data reproducibility.  The study was carried out by observing the molecules under study through their nonlinear optical vibrational fingerprints in the spectral range from 2500 to 4000 cm-1, which covers the CH and OH vibrations of the selected media. It was found that the results are highly dependent on the nature of the sapphire surface. In the literature, it has been speculated that a strongly bound water layer exists on the sapphire surface prepared and cleaned with a given procedure. All the reactions found and observed in the present study could be explained in terms of hydrogen bonding competition.  Meanwhile and marginal off the presented study, two novel spectroscopic techniques were developed. It is assumed that these techniques will be useful in future work on the adsorption kinetics of organic molecules and compounds of different kind. The first technique was the development of a real time spatially and temporally resolved sum frequency generation system based on a broadband femtosecond laser source. The second technique was a combination of in-situ Second Harmonic Generation (SHG) and Ellipsometry to probe surface coverage and thickness of adsorbed layers of the Self-assembled organic Monolayers (SAMs) simultaneously and in real time.