Grain size estimation in glacing angle XRD

[zhanghe]

Hello everyone,

I met a problem in XRD. Using theta-2theta mode I can not find crystalline peaks in my thin film sample because most within it is amorphous phase. However, I get three clear peaks using the glacing mode,i.e. theta-theta mode. Now i want to calculate the grain size in terms of Scherrer equation, May I use the FWHM from the glacing angle results?
they told me the FWHM is not correct in the glacing mode,because the silt is varying bla bla.., so I think, the Beta in Scherrer equation is the change between crystalline powder and my sample, maybe I should measure a crystalline powder sample in glacing angle, and then comparing them, I can get the grain size, Am I right?

zhanghe

 

[BigJDubs]

No, you cannot use the FWHM from the glancing angle results to calculate grain size. The peak width in glancing angle mode is a function of both the crystallite size and the preferred orientation of the grains in the sample. Therefore, the peak broadening due to strain and preferred orientation cannot be separated from the peak broadening due to crystallite size. To accurately measure grain size, you need to measure the peak width in the theta-2theta mode, which is not affected by strain and preferred orientation.