We observed an increasing dependence of real dielectric constant on wave length in thin polymer film. The wave lengths we used are well far from absorption ones. How this can be explained?
Dear Gene Whyman,
How did you measure and theoretical model it? The abnormal behaviour very much depends on the assumption you used.
Best wishes
Xuhua
I do not know the details of your sample or measurement setup. What I would investigate in a case like yours is the possibility that the substrate on which the film is deposited (if you are talking of a supported film) may play a role in the optical response in the wavelength range examined. Being far from absorption range, transmittance should dominate, and the back-reflection / absorption at the underlying interface with the substrate may interfere to some extent with the incoming propagation (and this could be more effective if the film thickness is comparable to the used wavelength).
Dear Gene Whyman , which technique you used to determine the real dielectric function? Because if you assume that there is no absorption (k = 0), a mathematical model like Cauchy and Sellmeier could be appropriated. If you run an ellipsometry analysis you could use several models to compare the results.
Another point to account for, is the real dielectric function depends on the refractive index (n) and the extinction coefficient (k, which is linked to the absorption coefficient alpha), as e1 = n² - k² and e2 = 2nk; so the real dielectric function (e1) do not has a linear correlation with the absorption, so the increase could be on the refractive index of the sample. Did you manage to investigate the imaginary dielectric function?
Best regards,
Gustavo.
Note: Cauchy and Sellmeier models assumes that e2 = 0, since there is no absorption (k = 0).
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