Optical and magneto-optical characterization of thin films of functionalized tetraphenylporphyrins

The anisotropic optical constants of vacuum deposited films of H2TMPP, CuTMPP, and NiTMPP (TMPP = 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin) in the thickness range of 50 to 150 nm were obtained by spectroscopic ellipsometry measurements and subsequent modelling. The angle of the planar molecular backbone with respect to the substrate plane was determined from the degree of optical anisotropy of the optical constants. The resulting angles were compared to those of near edge X-ray absorption fine structure (NEXAFS) spectroscopy on 2 to 5 nm thick films. Gold and natively oxidised silicon were used as substrates. The molecular tilt angle on Si (~ 38°) was found to be slightly smaller than on gold (~ 41°) for the thick films. This trend was confirmed by NEXAFS. Magneto-optical Kerr effect spectroscopy was applied in order to obtain the off-diagonal elements of the dielectric tensor under a magnetic field. These results were then used to calculate magnetic circular dichroism spectra for comparison with literature results and the assignment of Faraday terms to the particular absorption features.