Kunlin,

You just need to prepare a random mat, be careful for surface of mat, and punch it to your xrd-sample holder size and try to cover sample holder (or fill). You can get lttl bit noise but you can get rough test results

Thanks. 

use spin coating on silicon wafer 

Just prepare randomly or aligned deposited nanofiber mat. Then cut them in the size for XRD holder. There are some differences with different assembly nanofiber mat. Make the mat not too thin, or you can't get enough signal from the XRD machine. 

It will depend on the information that you want to obtain......for crystallinity information the above considerations are perfect, but if you want to study polymer chain alignment inside of each fiber the procedure is quite different

yours

Make sure you fix your sample to a piece of glass and then fix it to the holder, so you don't get the peaks from sample holder or Plasticine .

Regards