gtacchi - 22-2-2005 at 05:04
Anyone knows how to make the calculation to obtain the thickness of a thin film in a glass with a transmission spectra UV-Vis?
unionised - 22-2-2005 at 11:59
Yes, provided that the thin film is something that absorbs light or that it has a different refractive index from the glass.
You can look up stuff about interference effects for the usual textbook answer.
Find a wavelength where the film absorbs but the glass substrate doesn't.
Measure the absorbance of the film at that wavelength.
Make a solution of the stuff and measure its absorbance with a known pathlength.
From the concentration in the solution, you can calculate the amount of stuff in a given area of solution (for the given pathlength).
For example, say you get half an absorbance unit for a 1% solution with a 1 cm pathlength.
1% is 1g/100 ml, that's 0.01g/ml. For a 1 cm path that means you have 0.01g covering each square cm of the cell.
If 0.01g/cm^2 gives 0.5 absorbance units then 0.02g/cm^2 would give 1 absorbance unit.
If the thin film has an absorbance of (for example) 1.3 absorbance units it must be 1.3* 0.02 g/ cm ^2.
From that, and the density, you can calculate the thickness.
(There are problems with this method involving deviations from the absorbance laws with high concentrations, I did use it once, but I was able to use
a dilute solution of a dye in the film)
[Edited on 22-2-2005 by unionised]
[Edited on 22-2-2005 by unionised]