I usually perform the calculations of gap for monolayers with the formula [(Alph HNu *) ^ 0.5 = f (HNu)] because the interference fringes have a comode behavior (transmission maxima gradually decreases towards the lower wavelengths). But with multilayer I observe this phenomenon (where transmission maxima does not decrease towards lower wavelengths ?) That makes me doubt the applicability of the aforementioned algorithm.
Thak You
Dear Mohand Arezki OUADFEL, it is seen from the attached figure that the films are thick (maybe around micron) - a lot of peaks exist. Therefore to call them "monolayers" is inappropriate. Besides both films even in singlelayer form are inhomogenous across the thickness, i.e the optical properties on top and bottom interfaces are different. If you compare the peaks amplitude of C1 and C2 you will see that both films have different refractive index, C1 being with the higher one. Therefore you have a double layer systemconsisting of two materials with different properties. I can not get the physical meaning of optical band gap of the double layer system and I think that it is not correct to define it.
Hi Dr Tsevetanka. So you means it's not appropriate to study the double layer its self by transmission spectroscopy, in order to get its optical parameters.
And even if I elaborate multilayer formed by Homogeneous sinble layers I can not consider it as an inhomogeous layer made of two layers!!! What I mean is, how to study it as a Layer if i can not define an optical gap (Eg= f(Eg1,Eg2) and so on? (I know i can performe Spectroscopic Ellipsometry to get physical parameters of each layer)
Dear Mohand, yes, it is exactly what I meant - it is incorrect to regard double layer system as a single layer with effective optical parameters (refractive index, optical band gap, etc.). You can study your sample by UV-VIS-Spectroscopy and ellipsometry but for calculation of optical parameters you should use multilayered model. If you want to prepare an effective media consisting of both materials you can try to deposit alternatevly many layers with small thicknesses (5-10 nm). Good luck!
Hi dear
" but for calculation of optical parameters you should use multi layered model" This is exactly what i wanted to hear. But i'm still at the "HOW TO DO?!!!" step
Thanks again!!!
Could you, please, explain what exactly you want to do. When I say "calculation of optical parameters" I mean that you have a multilayered system and you want to determine optical constants and thicknesses of the films. One possible way is to measure T and/or R (transmittance and reflectance, respectively) and perform non-linear curve fitting. The last means to minimize the discrepancies between measured and calculated spectra. To calculate the spectra you need some model. Here I advice you to use multilayered model: known substrate, layer 1 with n1, k1 and d1, layer2 with n2, k2, and d2, etc. The parameters n1, k1,....are varyied until a match between measured and calculated spectra are obtained. Hope this helps.
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