NetNotes


I would like to second Phil Oshel’s comments. Voltage and


signal are both critical. I have some images collected from par- ticles dispersed in a polymer matrix (ſtp://ſtp.marl.iastate.edu/_ Gallery/Voltage%20effect/). Te particles are generally below the surface. Substantial voltage is needed to get a good outline of the particles. Tere is a big difference between 20 and 30 kV for the GaIn particles. Te BSE signal provides more particle info than does SE. (Refer to the TiO2


samples at 10 or 20 kV.) A


simulation of the different signals at different voltages would be helpful, especially if you can model the particle in its environ- ment. It would be good to have a dedicated BSE detector rather than using the BSE mode of an ETD secondary electron detector. Te latter is a poor substitute. For a pole piece-mounted detector, shorter working distances are good. We normally image samples at 10 mm working distances in our Quanta. I will shorten the distance for samples with weak signals. However, I am careful not to shorten it too much or I lose signal strength. More of the BSEs head up the column than hit the detector. Of course, for in-column detectors, short working distances are good. We don’t know much about particle size or loading. We were told that “ Particles were applied in a paste to <snip> FTO substrate on glass”. For the record, FTO is fluorine-doped tin oxide, NOT titanium oxide. It is used to provide conductivity to glass sub- strates. It is also not particularly smooth. It clearly has texture at high magnification. It is good that the film was grounded. FTO renders the glass surface conductive. It does not render the thick- ness conductive. You need a bridge across the glass thickness. It would be nice to know what size the particles are and what liquid was used to make the paste. You say the film was baked over- night. It seems that you do not want to have any carrier leſt aſter- wards. You could have a double-bind there. If the carrier is fully volatile, heat alone should remove it with temperature. However, if it needs oxygen to burn the carrier off, then you also run a risk of oxidizing the metal particles. You may be trying to find a temperature that effectively completes the one without starting the other. Tere is likely no sharp temperature cutoff. Even if the carrier is volatile, it probably has components that will remain at high temperatures. Have you tried cooking the carrier alone on a clean substrate in the absence of iron particles? Do you truly end up residue-free? I predict not. Tat is probably the reason for C in your X-ray spectrum. So, I am guessing that you are looking for a layer of only Fe nanoparticles. Te carrier should be all re- moved. However, I suspect you have a residual organic meniscus around the Fe particles. You may not be able to distinguish the difference between Fe and organic material in SE. You should see a clear difference in BSE at the right voltage. Too much voltage (like 20 kV) and you will blast through the meniscus and just see fuzzy edges. Too low a voltage (perhaps 2 kV) and you will image only the surface of the meniscus. We commonly start at 10 kV and work from there. Multiple voltages may be beneficial. Unless your particles have their fields aligned with each other, I really don’t expect magnetism to be a problem. We have looked at magnetic samples successfully. Tey need to be kept small or I run out of stigmator correction, and that is clearly obvious. Warren Straszheim wesaia@iastate.edu


Sending samples through the mail Microscopy Listserver Hello all. Has anyone had experience


2022 July • www.microscopy-today.com


Any suggestions are welcome. Tank you. Rebecca Jackson rebecca.jackson@utsouthwestern.edu


We have. We instruct our clients to fix the samples as usual,


do the buffer washes, and ship the samples to us in the buffer. Leona Cohen-Gould lcgould@med.cornell.edu


I do not know if there are regulations in your country that


prohibit sending specimens in aldehydes through regular mail. If so, shipment of aldehyde-fixed specimens in buffer may be a so- lution. I recommend including a sodium borohydride treatment step in the protocol to avoid possible negative effects on ultrastruc- ture. When using formaldehyde or a mixed fixative with formal- dehyde and a low concentration of glutaraldehyde, remember that fixation may be reversed over time if the specimens are stored in buffer. Tis can be prevented by including a 0.1–1% sodium bo- rohydride step in the protocol, see, for example, https://journals .sagepub.com/doi/pdf/10.1177/31.2.6339606. Peter van de Plas p.vandeplas@aurion.nl


We work with samples sent through the mail all the time (en-


dometrial tissue for SEM analysis). We provide the doctor a vial containing the fixative (we use 2% glutaraldehyde in PBS). Te doc- tor places the tissue in the vial and sends it to our lab. We analyze a portion, and the rest of the tissue is stored in the same fixative. We have analyzed tissue stored for >10 years in the fixative and it was intact. Yorgos Nikas eikonika@otenet


Tank you for the information! I will look into adding so-


dium borohydride if we need to ship in buffer. Rebecca Jackson rebecca.jackson@utsouthwestern.edu


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receiving or send-


ing EM samples through the mail? We have users that want to send us tissue in fixative, but I am not sure what to tell them.


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