Spectroscopic ellipsometry on a novel cyanine dyes in Langmuir–Blodgett multilayers

We have investigated on cyanine dye (HQ) in Langmuir–Blodgett (LB) films by spectroscopic ellipsometer (SE) and compared the results with that obtained by using small angle X-ray diffraction (SAXD). It is found from the isotherms that there is a critical point on Langmuir films near the area 0.8 nm2/molecule for HQ LB films with and without Cd2+ ions, respectively and suggested that the facts should result from the phase transition due to the change of molecular tilt angle on surface of sub-phase. The refractive indexes as a function of the wavelength λ are reported by the SE method using the three layers-model (air-LB film-silicon wafer) and Cauchy dispersion equation, for the first time presented in literature. The thickness of a single deposited layer is 2.45 nm on average. The thickness of per monolayer is agreement with those obtained by SAXD measurements.