There is an X-ray method to measure the thickness of a thin film, however it works best in the 1 to 100 nm range. It's called XRR (X ray reflectommetry), and is based on the interferences of an X-ray beam penatrationg at very low angle in a film and reflected and transmitted at the different interfaces.

http://ia.physik.rwth-aachen.de/methods/xray/www-xray-eng.pdf

http://en.wikipedia.org/wiki/X-ray_reflectivity

The X-ray penetration into a material depends on the incident angle. So you may try low-angle diffraction. However it is too tedious way to go so I'd rather used some of the methods suggested by Mahdiyar.

There is an X-ray method to measure the thickness of a thin film, however it works best in the 1 to 100 nm range. It's called XRR (X ray reflectommetry), and is based on the interferences of an X-ray beam penatrationg at very low angle in a film and reflected and transmitted at the different interfaces.

http://ia.physik.rwth-aachen.de/methods/xray/www-xray-eng.pdf

http://en.wikipedia.org/wiki/X-ray_reflectivity

You can estimate the thickness (at least for thin films) by the peak broadening of the XRD peaks using the Scherrer equation (http://en.wikipedia.org/wiki/Scherrer_equation). This may give a rough estimate, but could also just give you crystallite size. It does mean you don't have to take more measurements though. For accurate calibration you should use XRR though.

• What is the expected film thickness?
• What substrate?
• What sample size?
• Post your XRD data