NetNotes
months and the lenses at 40,000× when not doing microscopy which is typically 1000–10,000×. Larry Ackerman
larry.ackerman@ucsf. edu Mon Mar 21 To this point: in our faculty-EM-facility, we are using a 120
keV TEM, vintage 1990 - daily, with (regularly) 10+ different users. Standard voltage is 120 keV, always, for more than 18 years. LaB6, always; lifetime; about 3 or up to 3.5 years. Vacuum excellent and stable: Rot, ODP plus IGP, plus always LN2; cryo cycle (IGP off) every evening for 4 hrs; computer-controlled HT and filament start every morning, with wobbling the HT at 120 keV. — LaB6 is cold for specimen change, always; re-heated for 19 × 5 sec, each time. Aſter this, we can start recording “equidense” images almost immediately (aſter 3 to 5 min “searching”). —Yes, some Master or even PhD students don’t see or experience a change of a filament. (I have an old one, on the bench, for demo). We take digital micrographs on a 12 bit 1k camera for the last 12 years, with lots of stitching, daily, and never experience problems with instability or uneven or varying density (at least not observed / observable!). We do take montages with usually 4 × 4, up to 8 × 8 (or more) frames. —If there are problems, then they are related to “too old” dark and flat fields, which are used for correcting the digital images. Dark/Flat fields are needed about once a week, but sometimes only every 2 or 3 weeks. (no cryo work at very low dose!) —Only problems are when working with new or old filament. Reinhard Rachel
reinhard.rachel@biologie.uni-regensburg. de Mon Mar 21 Aſter many years of taking commissioning test pictures to prove
the performance of TEM and SEM it is clear there are a number of features that need to be taken into account. In my early days as a service technician (probably 1965 to 1970) I was amazed how it always took me about three hours to “get in the groove” when I was taking pictures for final commissioning. Ten I noticed if I simply switched the high voltage on, with the specimen in the instrument, and to return about two to three hours later, I had a test picture within half an hour. Eureka, when I then realized about high voltage stability—heat gained must equal heat lost. Having a very nice meal with a client one evening he suggested that we go back to the lab and I take a test picture on the TEM that they have just moved from one lab to another. With the same simplistic reasoning I thought “Oh no three hours!” But I had forgotten the instrument had a gas filled tank and was thrilled to within forty five minutes have the test resolution actually visible on the screen; no picture required! Silly me, I always thought they gave us a gas filled tank so it was less of a mess going in to change components, not that it cut down mass! Working with automated analytical SEM we found that the backscattered electron results and x-ray emission did not become stable for some hours aſter specimen exchange. Investigating the problem, colleagues found that when the vacuum in the gun became absolutely stable so did the results! Outgassing the samples prior to placing them in the microscope halved the time for stability to be reached. Of course a cathode assembly will need to become thermally stable, but it is the other areas that take the longest time. So putting all the knowledge together here are the results—Transmission Instruments: (1) High voltage generator—the critical period is the time taken for heat gained to equal heat lost once the high voltage has been switched on. Tis relates to the type of high voltage tank (generator box if you like). (a) Oil filled tanks take up to three hours to stabilize depending on how large the tank is. (b) Gas filled tanks generally take about an hour or so to reach stability. (2) Te vacuum system in the gun also has to be absolutely stable, the speed of pumping matching the leakage. Tis will relate to when the gun chamber was last opened.
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Scanning Instruments: (1) Te high voltage tank is very much smaller and in general stability is reached within a hour. (2) If the electron gun is brought to atmosphere each time a specimen is exchanged, depending how gassy the routine specimens are, it may take over two hours for the gun vacuum to stabilize. Both of these sets of comments assume that there are no electronic problems with the instruments high voltage circuitry. Steve Chapman
protrain@emcourses.com Tue Mar 22
TEM: diffraction pattern I am looking for some tips to collect a diffraction pattern of
nanoparticles using a TEM JEM2100 with a high resolution camera Gatan Orius SC600, without damaging the sensitive CCD. I appreciate any help. Marcela Redigolo
marcela.redigolo@
mail.wvu.edu Tu Mar 31 Your TEM needs to have a beam stop above the camera to capture
diffraction patterns. Typically this is inserted and adjusted with a small knob on the side of the column just above the viewing chamber. Normally you would get the diffraction pattern you want to record on the fluorescent viewing screen, then insert the beam stop to a point that covers the bright central incident spot of the diffraction pattern, and then reduce the brightness of the pattern as much as possible with the brightness/intensity/C2 knob to reduce the possibility of damage to the CCD. Aſter this is done it should be ok to liſt the fluorescent screen and acquire an image with the camera. Once you have acquired the image, immediately lower the fluorescent screen again to protect the CCD. If you need to change camera lengths, do not do this while the pattern is being viewed/recorded on the camera because the pattern may change position and the central spot could move away from the beam stop and damage the CCD. Bradford Ross
bnross@interchange.ubc.ca Tu Mar 31 Tanks for your reply! Tis is the process I am used to when
working with other TEMs. Tis TEM we have has two cameras. Te upper one used for great part of the measurements, and the SC600 that was installed for high resolution imaging for certain interface analyses. I was wondering if, different from the usual process, is there any other settings to use with this camera without causing damage. I am new to this microscope and apparently, in the past someone caused a damage to the camera, because of the diffraction pattern. It’s my belief that something was done wrong and the usual process would work just fine. But I decided to check just to be sure I’m not missing anything. Marcela Redigolo
marcela.redigolo@
mail.wvu.edu Tu Mar 31 If you have an Orius camera you are well set up for diffraction.
Tey are almost bullet proof and have anti-blooming, so spots stay sharp. If you are sensible and careful there is no need for a beam stop. Use small condenser apertures and parallel illumination with a selected area aperture and well-focused SADP, you can have the pattern on the screen for minutes with no obvious damage. Our camera was damaged by a user who had a large condenser aperture, no SA aperture, and an unfocused diffraction pattern giving a very high intensity caustic. Tat user didn’t really know what they were doing; before it would only been a sheet of film but getting a digital camera fixed is expensive. Richard Beanland
contact@integrityscientific.com Fri Apr 1 Occasionally we have requests for diffraction patterns on the
slow scan CCD camera on our FEGTEMs. Two tips I can offer are these: (1) Start with high spot sizes (high excitations of the first condenser lens). Tis will reduce the beam current, but improves
www.microscopy-today.com • 2011 July
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