Investigation of interfaces by second harmonic ellipsometry

Surface Second Harmonic Generation (SHG) and ellipsometry have been combined to give Second Harmonic Ellipsometry (SHE), a new technique, which already appears to be greater than the sum of the parent techniques.X-, Y- and Z-cut quartz crystals were available for investigation, though the structure (α- or β-) and the direction of optical rotation for these was unknown. The three flats were investigated by ellipsometry, SHG and (for Y- and Z-Cuts) SHE. The results and fits for Z-cut quartz are presented here. Transmission ellipsometric experiments revealed that the rotation was anticlockwise about the optic or Z- axis and that the specific rotation in/mm matched closely with literature values. Also the X- and Y-Cut materials gave results expected for birefringent crystals. SHG experiments further revealed that the quartz was trigonal in structure and therefore was α-quartz (β-quartz is hexagonal). The intensities are fitted to a trigonal model with the χ(2) components χxxx and χxyz being the only non-zero contributors. The presence of the chiral component, χzyz was particularly significant. The results for SHE are also presented, and the ellipsometric quantities Δ and Ψ are fitted.The dye molecule Rhodamine 6G (R6G) is also investigated by ellipsometry. Wavelength scans at variable angle of incidence and constant concentration, and fixed angle of incidence and variable concentration are presented. The results are fitted to give values of the refractive index components n and k for each wavelength. The model fits for all thicknesses over 10Å.Finally, initial results for SHE from Liquid interfaces are presented. The results for water (non-zero Δ) were sensitive enough to detect the presence of an organic impurity, which was missed by surface tension. Δ reverted to 0o when the water filters were replaced. Results from Rhodamine 6G are also presented.