I am working with polymer/cnt multilayer thin films, could anyone suggest me step by step methods to measure the thickness of these films with different number of bilayers using ellipsometry. I have no models of the materials in my instrument.
Substrate-glass/silicon(piranha treated)
1st layer-PVA
2nd layer-PSS+CNT dispersion
Samples to be analysed- 2, 4, 6, 8, 12..bilayers of PVA & (PSS+CNT) alternately deposited on a glass/silicon wafer.
As far as I know, you can choose the layers from the programme, when you add layer from the main bar. i.e. If you have two layers , choose the first one from down to the surface layer. And you should estimate the thickness of each layer. Then when you measure, you will have the final thickness of the layers together. If your CNT dispersed in the polymer, I think you can choose the polymer as one layer.
Note that you should have your material reference in the programme, if not you may choose the nearest material which may have similarity in their properties.
You need to feed in exact refractive index of the each component in ellipsometry program. If sample is thicker than 100nm, reinforce think film in epoxy, take fine cross section using cryo-microtome and take perpendicular SEM of the Epoxy block
I used to have a similar problem with transparent inorganic materials. There, I first performed a multi-sample-fit of the refractive index of layer one using three different samples with thicknesses of about 20, 30 and 40 nm. This way it is possible to avoid/reduce thickness/refractive index correlation. Then I chose one thickness (e.g. 30 nm) for layer one and made three more samples with thicknesses of layer two like 20, 30, 40 nm on top of layer one and performed another multi-sample-fit in order to obtain the dielectric function of layer two.
As model dielectric functions you could start with a Cauchy function (A+B/lambda²+C/lambda^4 etc.) or a function by Yao et al. (A+B/lambda+C/lambda² etc.) with k=0 (if they are transparent). There are also other model dielectric functions, of course.
Step 1: Place sample on lab bench
Step 2: Carefully lift ellipsometer above your head and use it to smash your sample.
Step 3: Measure film thickness in SEM/TEM.
Sorry for the silly answer, but you won't like my real one: I'm not confident this measurement can be made with an ellipsometer. The reason is not that the models are not included in your software (which is also a problem), it is to do with the impact of the CNTs on your sample. Ellipsometry measures the depolarization of scattered light from your sample; CNTs, due to their very high aspect ratio, induce anisotropic Rayleigh scattering, which is going to pollute the quality of the light reflected by the sample and collected by the instrument. The existence of Rayleigh scattering alone would reduce the signal collected by the detector, and anisotropic scattering is going to mess up a depolarization measurement. Your model may fit the data collected, but you need to be very careful to repeat at multiple collection angles to provide consistency.
Please do let me know if you are finally able to make a measurement you believe with an ellipsometer, I would be very curious to know how you accomplished it.
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