While X-Ray reflectivity fitting from Globalfit software, intermediate layer of SiOx between the Silicon substrate and the film is showing higher roughness value than its thickness.
I read those, but I am searching a mathematical range/domain conditions. Also as Thickness is average of all heights from substrate and roughness is average (Ra) or rms average (Rq) of differences from the thickness. So a Mathematical formulation approach can help which can show the range or domain for conditions, if one can put here.