A comparison of the optical constants of aligned and unaligned thin polyfluorene films

Abstract

The optical constants of aligned and unaligned thin polyfluorene films have been investigated using variable angle spectroscopic ellipsometry over the spectral range 250–1000nm. Films were prepared by spin coating, with alignment achieved by deposition on a rubbed polyimide substrate followed by annealing. The films could be well modeled by layers with uniaxial anisotropy. The unaligned film had its optical axis oriented normal to the film surface and was optically negative. There was large absorption and dispersion of the refractive index perpendicular to the optical axis and small absorption and dispersion of the refractive index parallel to it. The aligned film had its optical axis oriented in plane, normal to the rubbing direction, and was optically positive. There was large absorption and dispersion of the refractive index parallel to the optical axis and small absorption and dispersion of the refractive index perpendicular to it. These results will be useful in the design of polarized light-emitting devices using polyfluorene as an active layer.