Circular birefringence dependence on chiral film porosity.

Obliquely deposited thin films with helical microstructures exhibit circular Bragg effects. In this study, the effect of film porosity on the circular birefringence of helical thin films is investigated in TiO(2) films deposited at angles ranging from 30 degrees to 87 degrees in order to determine the various mechanisms responsible for the circular Bragg effects. Specular transmittance and diffuse scattering measurements indicate two film growth regimes of enhanced circular Bragg effects: The first regime is due to a maximum in form birefringence while the second regime is caused by strong anisotropic scattering.