Accurate determination of film thickness by low-angle X-ray reflection

A modified Bragg law for straightforward determining the film thickness by low-angle X-ray reflection was derived based on the geometrical optical the ory. We showed that this modified Bragg law and its inference formulae coul d be used to accurately determine the thickness of the monolayer or multila yer film. Furthermore, the modified Bragg law for determining the superlatt ice period presented earlier by others can be derived from the above modifi ed Bragg law. The similar inference formulae were also given. The precision in determining the film thickness and/or superlattice period by the above formulae was discussed.