Line-shape analysis of ellipsometric spectra on thin organic films

A methodology for the line-shape analysis of ellipsometric spectra on thin (<200-A) organic films is presented. Four different line shapes are employed: Gaussian, Lorentzian, phase-relaxed Lorentzian, and a critical-point line shape. An analysis of analytic data addresses the problem of the modeling of unsymmetric absorption bands. The method is exemplified by an analysis of thin films of phthalocyanine and poly(3-hexylthiophene), and we show that the number and type of resonances in an absorption band can be obtained. The possibility of resolving the cause of a shift in the peak position of an absorption band is also demonstrated. In the case being studied the shift is due to the redistribution of the oscillator strengths between the individual resonances in the band and not to shifts in the energies of the resonances.