How much more reliable is the comparison of transmission data and reflectance data for a thin film of polymer coated on ITO/glass and Platinum respectively?
I am electropolymerizing a polymer on ITO and platinum and find that there is a huge red shift (~ 40 nm) in the visible absorption spectra of polymer on platinum compared to that on ITO. Since absorption is recorded in transmittance mode on ITO and reflectance mode on platinum, is it reliable to compare these two results and conclude that the polymer formed on platinum is different than that on ITO.
Thanks!
Thank you for clarification. My answer is definitely NO. It is not correct to make a conclusion of the absorption properties of thin film on the basis of measuring its spectra onto different substrates. If you want to compare both layers you should calculate their optical constants (refractive index and extinction coefficient) because they are function of films structures, chemical compositions, morphologies etc. and do not depend on the substrate types.
Thanks a lot for you answer.
I would like to explain here, one of my experimental result which needs more clarification. I am restricted to use my polymer films supported on substrate. I have to do measurements on different substrate surfaces only, which require different modes (transmission mode for ITO and reflection mode for platinum).
In one of my experiment, I polymerized my polymer on both the surfaces and measured absorbance at Lmax for different thicknesses of the growing film. Absorbance should increase with increasing thickness and might/might not be linear according to Lambert-Beer's law since this is an aggregated system. Interestingly, polymer growing on platinum is pretty much linear compared to polymer on ITO which is also linear initially but deviate from linearity very soon. The slope of this plot is more for the polymer polymerized on Pt compared to that on ITO. This indicated that the polymer growing on platinum has more absorption coefficient than that on ITO. Since The mode of measurement is not same, can I draw such conclusion?
Find the plot attached with this. X-axis is polymerization charge density which is proportional to thickness.
Dear Rekha Singh, thank you for the detailed explanation. There is one thing that I couldn't understand. How you calculate absorbance in the case of reflectance measurements onto Pt substrate
T+R+A =1
Since T = 0 in reflection measurements, R was converted to A. Ocean optics software gives absorption spectra for reflection measurements too. So it is converted by software considering R as T.
I should note that absorbance and absorption are two different parameters. Absorbance is -log(T), where T is transmittance. Absorption is 1-R-T-S, where R, T and S are reflectance, transmittance and scattering. So, please specify what do you measure absorbance or absorption.
it is absorbance which the spectrometer records. Simultaneously it give transmittance spectra also which is related logarithmically to absorbance. In case of reflectance measurements there are only absorbance and reflectance values which we get.
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