LANGMUIR-BLODGETT FILMS FOR SECOND HARMONIC GENERATION

Available from UMI in association with The British Library.; A new design of constant perimeter Langmuir-Blodgett (LB) trough has been developed based on a diamond-shaped barrier which flexes at the corners to alter the area. The new trough has several advantages over existing commercial models the major ones being ease of construction and high cleanliness.; Trough performance was initially evaluated with eicosanoic acid, tricosanoic acid and 22-tricosenoic acid. Isotherms of these three materials show excellent reproducibility and compare favourably with published data. Optimum conditions for deposition have been established for each of the fatty acids. The quality of the deposited films, as judged by optical and electron microscopy, is very good. During deposition the amplitude of surface waves was of the order of 1 m and monolayer flow patterns appeared satisfactory.; The monolayer properties of three amphiphilic azo dye derivatives were studied and LB films were deposited onto silicon and glass substrates. The optical properties of the deposited dyes were investigated using absorption and second harmonic generation measurements. Two of the materials form good quality LB films and large second order effects were observed with estimated molecular hyperpolarisabilities of (3.3 {dollar}pm{dollar} 1.8) {dollar}times{dollar} 10{dollar}sp{lcub}-49{rcub}{dollar} C{dollar}sp3{dollar} m{dollar}sp3{dollar} J{dollar}sp{lcub}-2{rcub}{dollar} and (7.4 {dollar}pm{dollar} 5.6) {dollar}times{dollar} 10{dollar}sp{lcub}-49{rcub}{dollar} C{dollar}sp3{dollar} m{dollar}sp3{dollar} J{dollar}sp{lcub}-2{rcub}{dollar}. The lower figure could be enhanced by depositing the dye from an acidified subphase. The SHG signal produced by an alternating bilayer of the two dyes was much lower than expected. This is possibly due to a proton transfer between the two components of the composite film.; A technique to determine the thickness and refractive indices of LB films from multiple angle reflectivity measurements has been developed. Dispersion curves and thickness per monolayer values have been calculated for multilayers of 22-tricosenoic acid and one of the azo dye derivatives.