Zapperz,
I have made an extensive web search about RHEED experimentation.
I can see that electrons are accelerated to very high energies, they are diffracted by thin surfaces and a CCD camera (or equivalent detector) is used to capture diffracted images that are very very small due to de very small wavelenght2 of the electrons. After this stages the digitalized images are sent to a computer for image processing and análisis.
For example we can visit:
http://www.geocities.com/CapeCanaveral/5702/Fe_Si.html"
I can see that in all the visited pages the interest of the researchers is focused on the images they obtain to deduce the properties of the chrystaline surfaces and not the análisis of the data necessary to verify De Broglie's formula.
In the amplification of the images the real magnitude of the distances between the diffraction "spots" that appear is lost!
I can state that the verification of the De Broglie for relativistic mass haven't been done yet!
I realize now that all the technology necessary to do the experiment I propose is available, just only the goal to verify the De Broglie formula must rise!
I strongly believe it is very important to do the verification of the dependency of mass with the velocity by a RHEED experiment and the De Broglie formula.