A few standard ways is to fit the "thin film model" to optical data such as ellipsometry, reflectometry, or a spectrophotometer as you have. A Woollam ellipsometer or a Filmetrics reflectometer come with software for thin film fitting. Most spectrophotometers don't. You can use paid software (MacLeod, Optilayer) or write a simple spreadsheet or use a general purpose programming language (Excel, Matlab, Python) to fit the data. Usually assumptions are made to reduce the index fitting to a few parameters (Cauchy model or whatever is appropriate for your polymer). The thin film model is described in Macleod's textbook in enough detail to implement in Excel, and for a single layer the model is simple enough that you can probably find it online, but I don't have a link to give. The accuracy of the fitted index and thickness from the spectrophotometer goes up as you collect polarized data or data at multiple incident angles, if you have that ability. It is less accurate for thin films and if you have the option, putting down 500-1500 nm gives you a better ability to fit.

To measure the thickness and refractive index of a polymer film deposited on a glass substrate using the available devices of spectrophotometers, Michelson interferometers, and Abbe refractometers, you can use the following methods:

So, the thickness and refractive index of a polymer film deposited on a glass substrate can be measured using spectrophotometers, Michelson interferometers, and Abbe refractometers. The specific method used will depend on the available equipment and the properties of the film being measured.

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There are several techniques that can be used to measure the thickness and refractive index of a polymer film deposited on a glass substrate, including:

Of course, AFM is the fastest and most usable technique among them.

Best regards.