Hello Ahmed,

If you have interference pattern in your transmittance spectra, take a look on this article. Best regards

Alaa

Film thickness can be measured on a UV-Visible spectrophotometer

by using the interference effect of light. Constructive

and destructive interferences between light reflected from

the surface of the film and the base material result in an

interference pattern with a period between peaks that is a

function of the wavelength (Figure 1). Film Thickness (d )

is obtained using the following equation for a known

refractive index:

Where d = film thickness in µm

w = number of complete waves over the wavelength range

η = refractive index of the film material

θ = angle of incidence (34° for this accessory)

λ1 = short wavelength limit for wave counting

λ2 = long wavelength limit for wave counting

I may add, that if you do not know the refractive index of your material you can measure the interference pattern perpendicularly to your film (as usually) and at other incident angle. You can then calculate refractive index from the shifts of extrema in your measured pattern.

There are some papers on the topic but also spectrometer manufacturers provide some useful hints:

https://www.perkinelmer.com/CMSResources/Images/44-153901APP_Thin-films.pdf

http://www.shimadzu.com/an/uv/support/uv/ap/film.html

Thank you all. that was very helpful

A special Thank you Alaa EL-din E. A. Ragab