Variable angle spectroscopic ellipsometry studies of oriented phthalocyanine films

Abstract

Thin films of metal-free phthalocyanine (H2Pc), vapor deposited onto sputtered copper substrates, are characterized using a fully automated Woollam variable angle spectroscopic ellipsometer. Data from over a dozen H2Pc films in the thickness range of 1000 to 1140 Å were acquired over a 4000–8000 Å wavelength range in 100 Å steps, and 45°–79° incidence angle range in 2° steps. Two classes of H2Pc films were formed, uniaxially oriented with the molecular stacking b axis in either a standing or surface-parallel configuration, by carrying out the deposition at two different substrate temperatures and deposition rates. Reflection absorption infrared spectroscopy was used to verify the different orientations. It is observed that the three dimensional plots of the ellipsometric parameters Δ and Ψ versus wavelength and incidence angle have different characteristic shapes for the two classes of oriented films, implying anisotropic dielectric functions. Using a multilayer optical modeling code capable of treating fully anisotropic films, we attempt to determine the in-plane and out-of-plane optical constants for each of these ‘‘orthogonally’’ oriented film types. Significant differences in the optical constant spectral solutions are found for the two classes when treated with isotropic film models, but convergent solutions of the direct anisotropic regression analyses have not been found. However, due to the high degree of uniaxial ordering in the two film classes, it is possible to extract approximate solutions to the parallel and perpendicular optical constants taken with respect to the crystalline b axis.