NetNotes
is a researcher bothered by them? Well, the answer is simple but sometimes difficult to say. To appreciate morphology needs affection, brain and time. That makes it less attractive to people inclined to approaches that are easier to interpret, such as immuno- logical and molecular ones. In Biology, morphology studies will remain the most straightforward approach to this hidden universe called microcosm. Morphology is a Queen that will always award her devotees! I just finished a long series of SEM shoots, it is above midnight here and I felt I have to defend my Queen. Yorgos Nikas
eikonika@otenet.gr Tue Sep 15 Absolutely! Time is expensive! T e time taken to treat the plants or animals, take samples, process them, etc. Imaging is cheap, and you don’t want to have to go back and redo imaging because you didn’t have enough samples to begin with. And sectioning doesn’t take that long for an experienced person. Nor is it much more eff ort to run multiple samples. As an aside, in plant biology, it sometimes takes a year to get transgenics, yet people are oſt en still unwilling to spend more than about a minute taking the key image showing the phenotype/gene expression. Another question is how many replicates are needed in experiments - for statistical diff erences to be detected? Also, how do you know what are the representative morphologies without multiple samples? Is any quantifi cation needed? It oſt en is, these days, you can’t get away with saying “this is a representative image” so much anymore. And if you don’t look closely at your tissues and cells, you might miss something subtle. Rosemary White
rosemary.white@csiro.au Tue Sep 15
TEM: tilting effect on camera constant We have a mineralogy grad student who doing selected area
electron diff raction (SAED) on single mineral grains and is collecting patterns while tilting the sample holder [X-tilt only between 0–20 degrees]. T e student is careful and thorough and is worried that the tilt will change her camera constant. To what degree does stage tilt aff ect the camera constant, and is there a recognized way to compensate for the change? Any assistance, suggestion, or reference is appreciated. Tom Williams
tomw@uidaho.edu T u Oct 8 T e problem, as you rightly understand, is that a focal length change in the objective lens will change the camera constant. T ere are two ways to correct this type of problem—either set the eucentric point very accurately prior to tilting, or always focus the tilted specimen by using the eucentric height control (Z’). Either method is acceptable, but I would use the latter in preference. Steve Chapman protrain@
emcourses.com Fri Oct 9
SEM: 30KV fails automatically We are using a FEI Nova NanoSEM450. Whenever we use the
30 kV, it only last for around 5 hours before it fails. And if we turn on the beam again using 30 kV, it will turn off instantly again. But it allows us to use 30kV the next day, and of course still only 5 hours. T e 20 kV and lower work fi ne. T e technician checked everything but didn’t fi nd any problem. Jason
13qw9@queensu.ca Fri Sep 11
We had a similar problem with a Philips CM200 that would arc
at 200 kV aſt er several hours. Still had the problem aſt er replacing the entire emission chamber. It turned out to be a DC power supply that regulated the high voltage. A 15 volt DC supply would start losing voltage causing the high voltage tank to increase to 220 kV plus then arc. It took a rookie service engineer, Ken Hurst, to setup a laptop to read all of the DC power supplies to fi nd the one causing the problem. David Hull
drhull@zoominternet.net Fri Sep 11
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1-800-538-3672 EDX: origin of X-rays 0-100 eV energy
A typical energy dispersive X-ray spectrum recorded using a TEM or SEM has peaks corresponding to characteristic X-ray energies, superimposed on a Bremsstrahlung background. I notice there is a zero peak followed by some background with reasonable intensity and it appears diff erently by diff erent detector manufacture in terms of intensity. I understand that ionization process results in the characteristic X-ray peaks. But, what process or electron/matter interactions could be involved to give the X-rays at low energy up to 100eV? My detector registered X-ray counts there; it must have come from somewhere. I would be extremely grateful if you could give me some hints, or suggest some book chapters to read, or some papers to refer to. Zhaoxia Zhou
z.zhou@lboro.ac.uk Wed Sep 9 T e fact that this zero peak appears diff erent from detector to detector is your clue to the origin, a peak or peaks in this region is almost certainly an instrumental eff ect, and not x-rays. T e various components in the detector and processing electronics generate some electronic noise which is digitized along with the true x-rays generated from the sample. Most pulse processors have a set of discriminators that are set on installation to minimize the amount of these eff ect, but cannot eliminate them entirely. T is is true even if you have a recent “digital” pulse processor–there will still be some soſt ware settings that act to reduce the zero noise peak. Every manufacturer does this a bit diff erently hence the diff erence you see. If you can modify the discriminator setting on your unit try tweaking then a bit and you will see some interesting stuff . Proper discriminator settings are critical to getting good light element x-ray detection with proper peak shapes and peak positions. Jon McCarthy
jjmccarthy@wisc.edu Wed Sep 9
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