Hello,

I believe the reason is simple. They have rather large number and degree of irregularities and defects in their crystal structure. These irregularities show as amorphous in the diffractogram.

Do a image search in google for "quantum dot TEM" to see the atoms in quantum dots. The degree of irregularity and number of defects is very high. You can see the answer to your question in the images.

Best Regards

Marko

Prof. Baller's statement is true. You can check it from the images of quantum dots.