These threads about cracked crystals made me pretty worried about such possibility on our two SX machines. As far I looked through this forum, I found only reports about TAP and PET crystals cracking. I think I (very unfortunately) can report that the LLIF can crack too
(a very sudden (less than a week) intensity drop, and clear peak broadening with blunted top). This makes me to wonder what causes could be behind such a cracking. Could the high intensity X-rays contribute to that? Lately I was a bit experimenting with extremely high beam currents (up to 1000nA), could this fatigue the crystal structure of LLIF? (But I think some line of Cameca probes for metals and semiconductors has column tuned for beam currents up to and more than 10µA) Considering that detectors are arranged symmetrically, and if xtals are at similar distance to the sample it will take similar dose of X-rays. So the amount of energy going to the detectors (and XTALS) should be similar. (L)LIF is known to be much lower intensity then compared to LPET or TAP (maximum intensities are much lesser than obtainable on (L)PET or (L)TAP). So considering intensities of diffraction, the question arise - what happens with not diffracted photon energies? I guess these are converted into the heat of XTAL?
This can look like fundamental and quite stupid questions, but on our two machines I never saw any PET or TAP cracked, and now this LIF... One additional factor to take into account is that our standby procedure for affected Field emission equipped SXFive is tailored to prevent column and aperture contamination - that is for standby the e-beam is parked on the stage reference point, and to prevent apertures from unnecessary contamination the whole beam exiting the extractor (1µA) is passed through splash aperture (kind-of bypassing) and movable aperture is took out from the path (there is no aperture at 40µm aperture position, and such empty position is used). So my high current experiments was not creating any exotic conditions for the machine actually as it experiences such conditions every morning/night then finishing the list of programmed analytical work. Well, to be honest the reference point does not produce strong X-rays as the metal of shuttle got covered/beam deposited carbon contamination layer/rubble, thus X-rays from reference point is dominated with low energy C Ka X-rays. But maybe that is the main problem and killer of LIF, as LIF wont diffract any C Ka as it is completely out of range of LIF diffraction - without diffraction whole such X-ray radiation would be converted into heat, and thus LIF would be affected the most. Any ideas?
One is clear, I should modify the standby procedure. I am not sure if lowering stage out from spectrometer axis would not introduce some other problem (i.e. X-rays hitting some electronics of spectrometer turret...). Probably best thing would be to drill the hole at reference point there X-rays would be blanked at standby procedure on FE machine.
To see the latest forum posts scroll to the bottom of the main page and click on the View the most recent posts on the forum link