I have a collection of nanocomposite thin films and their corresponding transmittance spectra over a series of temperatures. How can I use these to determine the refractive index (n) and extinction coefficient (k) for the films?
EDIT: My transmittance data does not exhibit clear interference fringes (I'm using VO2-In2O3 nanocrystalline films). Is it still possible to determine optical constants?
EDIT2: I do have thickness measurements from profilometry. Is it possible to determine absorption (A) as a function of transmittance (T) using A=-log10(T)?
Dear Abraham
You can take transmission spectra as a function of wavelength in the range where you get interference fringes. Use Swanepoole method to find out optical constants like refractive constant, extinction coefficient as s function of wavelength. You can also calculate band gap of the material. The advantage of this method is that you don't need reflectance spectra. Moreover, you also do not need thickness measurements seperately. The only condition is that you should get interference fringes.
Dear colleague J. Abraham,
Have a nice time and good day.
Taking into the account the answer of Prof. DR. @Dr A. Kumar the attached paper teach you easy how to calculate n and k from transmittance spectra using Swanepoole method to calculate optical constants.
I wish this is useful and help you.
Yours
A. El-Denglawey
If you don't see an interference fringes in T spectra it is possible the sample to have some absorption or to be very thin and the distance between the peaks to be higher than the width of the spectral range of your measurements. Is there a possibility to measure reflectance as well? The only possibility to determine n, k and d simultaneously is to use an appropriate dispersion model for n and k for your sample and nonlinear minimization of the descrepancies between measured and calculated transmittance spectra. It will be nice if you get some idea about the thickness from independent measurement. Good luck.
To quote from Chap.7.4.6 of O. Stenzel's book The physics of thin film optical spectra: An introduction
" As shown in the previous sections, it is possible to provide explicit expressions for the spectra of a thin film sample if geometry and optical constants are known. It is however impossible to obtain explicit expressions for the optical constants as a function of the measured data."
Here some a useful resources. Check with Chapter 7 in:
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjU18b5qcHfAhXMLlAKHdDwBH8QFjAAegQICRAC&url=https%3A%2F%2Fwww.researchgate.net%2Fprofile%2FJerome_Polesel%2Fpost%2FWhat_is_the_correct_band_gap_determined_by_a_Tauc_plot%2Fattachment%2F59d620fc79197b807797f6da%2FAS%253A293973668188172%25401447100192588%2Fdownload%2FThe%2BPhysics%2Bof%2BThin%2BFilm%2BOptical%2BSpectra_%2BAn%2BIntroduction.pdf&usg=AOvVaw31Ht7GF4cs3jMfQU_EXQzy
and here fom PE:
https://www.perkinelmer.com/lab-solutions/resources/docs/APP_Thin-films.pdf
plus a glimpse in yet another Stenzel book:
http://www.ciando.com/img/books/extract/3642540635_lp.pdf
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