| In this thesis, two optical techniques, angle resolved absorbance with photoacoustic detection (ARAPD) and second harmonic generation (SHG), were combined to characterize molecular orientation in organic thin films. The combination of these two techniques allows for determination of both the mean orientation angle and angular distribution width.; The molecular orientation of the azo dye, Disperse Red-1, in equilibrium at a fused-silica/2-propanol interface was investigated. Both ARAPD and SHG were used to measure the orientation in this system; however, the results could not be combined to yield a mean orientation angle and distribution width. Further characterization of the surface films was obtained by ellipsometry and atomic force microscopy, and all of the results indicated multiiayer formation.; A specific application of organic thin films is as alignment layers in liquid crystal devices. Molecular orientation studies were conducted on a model alignment layer composed of an azo dye covalently bound to a glass surface through tri- and mono-functional silane chemistry. SHG and ARAPD results for these films yielded a mean orientation angle and an angular distribution for each system. The films generated through mono-functional chemistry exhibited a narrowing of the angular distribution width in a non-hydrogen bonding solvent, whereas the tri-functional films showed no solvent dependence. Orientation insensitive SHG measurements indicated that surface coverage in the tri-functional silane film was twice that in the monofunctional silane film. The observed differences in solvent dependence is attributed to differences in the forces which dictate molecular orientation in the two systems.; The influence of interfacial index of refraction assumptions on optical molecular orientation measurements was explored, and it was found that the primary influence on the calculated orientation angles is the difference in index of refraction at the probe interface. The results illustrate the need to report assumptions of refractive index with molecular orientation measurements, and also demonstrate that a total internal reflection geometry is ideal for molecular orientation measurements. |
