NetNotes
products/#usb-video-grabbers Nathan McCorkle nmz787@gmail. com T u Oct 13
XEDS: problem with peak splitting
We have a problem with an older Noran Si(Li) detector running on a Voyager platform (it is about 19 years old!) that I have not come across before. Suddenly this week instead of getting a single peak, all of the peaks in the spectrum are split into doublets. For instance for Al K at 1.486keV we get two peaks separated by ~100eV and centered at 1.486keV. Has anybody seen this and is there a cure? Alan Nicholls
nicholls@uic.edu T u Oct 13
Sixteen years out from any contact with Amenex’s ETEC Autoprobe, I recall seeing line doubling when the detector was getting overloaded, especially in my hands. T e context is that I was trying to write code in TrueBasic to automate the process of setting the wavelength-dispersive spectrometers at the correct angle to detect the X rays coming from specifi c elements, whose wavelengths are ever so slightly dependent on their chemical surroundings. T e soſt ware was to scan across the selected wavelength and then select the angle at which the signal was at its maximum. Whenever the detector gain was excessive, the peak would get folded over onto itself, producing the false doublet. Just back off the gain setting. George Langford
amenex@amenex.com T u Oct 13 Are you talking about overflow in the MCA channels? I know we had an issue with that with a Tracor Northern 2000 system from back around 1980. We had a choice of confi guration between 24 bits per channel at 1024 channels or 16 bits per channel at 1536 channels. We opted for the second case and could get rollover in extreme cases. However, I think it looked diff erent than what Nicholl’s group has run into. Warren Straszheim
wesaia@iastate.edu T u Oct 13
TEM: mystery light fl ashes
We are using a JEOL 2100F electron microscope. In the past 2-3 days we can see a sudden “fl ash” of light on the fl uorescent screen along with a faint “click” sound. Rest of the TEM works as normal. This is more prevalent if I meddle too much with brightness knob. Can anyone suggest a reason for this? Amit Gupta
amit.welcomes.u@gmail.com Tue Oct 4
I believe you have seen an electric discharge. May be the connection between the screen and the ground is pretty bad. T is connection is done through a spring under the screen and the circuit for measuring the current received by the screen. Nicolas Stephant
nicolas.stephant@
univ-nantes.fr Tue Oct 4
Is there any outlet where I can measure and demonstrate the above—that is, any output like a ground wire where I can safely connect a multimeter and check? If it’s Wehnelt contamination, etc., can it be remedied without calling engineers? As there is no maintenance contract, I would like to provide rough estimate to administration before calling JEOL for help. Amit Gupta amit.welcomes.u@gmail. com Tue Oct 4
If you have arcing in the gun, you should get a Geiger counter and check for radiation. If your image shakes, rattles or rolls, then I might go with the gun. I agree, however, with the screen possibility. You may see arcs, but do you see the beam move? Or “fl utter” on the screen. Even worse, at high mag, is your focus unstable. If just fl ashes of light, but not the other phenomena, you might want to vent the camera - viewing area - and check under the screen. Note: Radio Shack has a glass fi ber “pen” that is designed to clean contact surfaces. If the spring is attached to ground, you might save your bosses a visit by
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cleaning the contact area on the bottom of the screen. Note: I have a rule about electron beams. When they misbehave, I always change the filament first. If there is no change, then, depending on age, I might save the fi lament. Note: Sometime, the gun housing just needs a good cleaning, but with my FEI/Philips Tecnai, there follows a lot of outgassing even after using the sun lamp to start the drying out. Fred Monson
fmonson@wcupa.edu Tue Oct 4 Since the 2100F is a FEG system, the gun components diff er than those described by some of the responses. I would avoid opening the FEG unless directed by service, or if you decide to replace the FEG tip. Replacement of FEG is not trivial (nor cheap), unlike W or LaB 6 , so this is not where I would start... T e click you are hearing is worrisome. Is it coming from the gun area (top of microscope)? Or perhaps from the HT tank behind the microscope? Try to determine whether the FEG emission current is fl uctuating shortly before or aſt er you hear this click. You may need to set up a camera or screen capture soſt ware to monitor the emission current (and vacuum levels!). If the click is coming from the gun area, this is usually indicative of arcing. Bad! Usually caused by lint/dust/particulate contamination in the gun region. T is would be unusual for a FEG. Has the FEG been opened in the recent past? If the noise is coming from the HT tank, then you may be experiencing a problem with the tank, which would necessitate a service call. Since this is the 2100 series, it must be relatively young, correct? Probably not an electronics issue, so I’m not sure why changing C2/C3 (brightness) knob would aff ect operation. As others have indicated, it could be related to charging of the InP screens (don’t forget little screen). But click noise means, in my opinion, more sinister problem that you need to fi nd. I hope not! Christopher Winkler
microwink@gmail.com Tue Oct 4
Besides the suggestions you have already received, when was the last time the gun and column were baked? T e clicking and fl uctuating condensers make me wonder if there is a bit of contamination on the condenser aperture. Baking might take care of that. Did this problem start after a particular sample was imaged? One that might cause contamination? Phil Oshel
oshel1pe@cmich.edu Wed Oct 5 T ank you everyone for help. T e fl ashes we observed were indeed
due to fl uorescent screen charging, further action awaits adminis- trative approval! For completion sake here is the summary: Problem: Bright fl ashes of light were observed with a click sound on fl uorescent screen. However, on suggestion from the listserver and further analysis: 1. No sound were heard when screen was “up” 2. No change in intensity seen on CCD camera 3. FE electron gun showed no change in intensity (looking through the window on electron gun) 4. No accelerating voltage fl uctuation 5. No vacuum pressure level fl uctuation of any kind 6. Flashes were more prominent during alignment (when image intensity will change a lot and screen will be thoroughly radiated due to various intensity wobbling, etc.) 7. Proper corona discharge kind of fl ash was also seen once or twice (at the edge of screen) 8. Issue disappeared on own for few weeks, now surfaced again Current reasoning: In JEOL JEM screen is held by 3 screws (as told by JEOL engineer) one of which is grounded, looks like ground screw is bit dodgy as the moment. I will let everyone know in case any development occurs. Amit Gupta amit.
welcomes.u@gmail.com Mon Oct 24
www.microscopy-today.com • 2017 January
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