NetNotes


are looking at both carbon rod coaters as well as a carbon thread coater. I would appreciate input on these two types of coaters. Pat McCurdy pmccurdy@colostate.edu


I have only done carbon rod and an old Gatan PECS ion deposition


system. My qualitative observations are below, and I have no financial interest in coating materials companies. Te PECS is slow, expensive to operate, and for our samples was limited to one at a time, but it worked well until we stopped maintaining it due to lack of use. We have a 10- year old EMS rod type turbo pumped carbon coater (not the one they currently sell). It works fine down to 3 nm on EBSD but is a bit trickier to get the desired thickness. Consistently sharpening the rod is key to getting a consistent thickness. Some of my geology users complain that they have to run two coating cycles since the sharpened rod will not get them to a 25 nm coat if they are going to microprobe. If you want a high-quality C coat high vacuum is a must. Greg Baty gbaty@pdx.ed


With due disclaimer that (a) I’ve been doing C coatings mostly for


charge mitigation on FIB circuit edit samples, and (b) below are per- sonal impressions and not a conclusion from any kind of comparative study: Te best (perceived as smoothest, cleanest, and most uniform) carbon coatings I’ve seen were produced by Gatan’s PECS system, us- ing ion sputtering. I haven’t operated PECS myself, but for me coatings made in it were perfect. Overall impression is that good cord and rod evaporation coatings typically come from turbo-pumped systems run by an operator with enough patience to wait for a full pump-down. I have been using the high-vacuum version of Safematic, and despite my initial skepticism I am very pleased with it. Automated exchange of evaporation cord is oh so convenient. No vested interest in Gatan/ AMETEK or Safematic. Valery Ray vray@partbeamsystech.com


Great question for the ListServ. Tere are advantages for both rod


and thread for carbon coating. Tere is also e-beam carbon and ther- mal evaporation which are more costly but can control a more precise and thinner layer. If you go with traditional rod or thread coating, then you should get a system with high vacuum (TMP) to have a finer grain size since you want a layer down to 5 nm. While a carbon rod can be more precise for very thin layers and finer grain size, some thread sys- tems can be pulsed, so the coating occurs slower to produce good con- trol of thin layers also. Tread systems are also a little easier to use since you do not have to sharpen and handle delicate carbon rods. A thread system would be good for new users that just want a quick conductive coating. Why compromise though? Tere are a couple of systems that can do both rod or thread, or rod capability can be added later as an up- grade. We offer such a coater: https://elementpi.com/sputter-coaters- carbon-evaporators/. Mike Toalson miketoalson@gmail.com


We have a Denton 502A Carbon Coater with a turbo molecu-


lar pump and Cressington thickness monitor. Using carbon rods, we deposit between 7–10 nm for CL and 20 nm for imaging, EDS, and EPMA. It has a cold finger so liquid nitrogen can be added to hasten a quick coat, otherwise an hour pump down gets us to 10−6


torr. The stage rotates as it is a line-of-site coater, 10 one-inch


rounds or maybe 5 thin sections can go in at one pump-down. We do a ton of EBSD but rely on a Leica Ace600 coater to apply a 1 nm coat of Iridium to any EBSD sample. It is flawless on geological thin sections and never charges. Bill Schneider wfschneider@wisc.edu


Cleaning Nickel Shim of Magnetic and/or Glass Particles Microscopy Listserver I have a nickel shim destined for nanoimprint lithography, made by


electroforming e-beam exposed photoresist. I don’t have a proper cleanroom, 2020 July • www.microscopy-today.com


but I’ve been trying to strip what seemed like residual ZEP e-beam resist and it has not been going so well. I’ve tried acetone, dichloromethane, n-methyl pyrrolidone, and 10% NaOH and sonicated with heat in both acetone and NaOH (at different times). Te NaOH is the most recent attempt, and it seemed to show improvement under FIB imaging, but I also noticed what appeared to be redeposition. I can only imagine this is due to particulate in my solvents, dirty air as I blow dry the shim or carry it from my sonicator to my FIB desk, or maybe insoluble particles like glass or ferromagnetic dust which start to settle onto the sample as soon as the sonicator is turned off. Features are around 150 nm linewidth, high frequency and complex shaped. So, lots of small approximately 500 nm sized holes/crevices which I thought was just diffusion limited for the solvent to get into and do its work. But now I’m confused. Should I invest in some .45- and .22-micron syringe filters for all my fluid work? Should I tape a magnet to the outside of the beaker I’ve been sonicating in to try and collect such particles? What is a standard semiconductor lab method for cleaning magnetic particles from magnetic layers? How about the idea of insolubles? Or can someone recommend a solution that will etch glass but not nickel? Nathan McCorkle nmz787@gmail.com


Did you try using a plasma cleaner for cleaning the surfaces and


also a plasma cleaner like the Evactron at the FIB chamber to keep the specimen clean during scanning? If you can mount the specimen with the surface to be cleaned facing down to the bottom of the beaker you might get rid of deposits coming from above. Another way to try to clean the surfaces might be to plunge in liquid nitrogen or to use a vacuum chamber with the cleaning solution and pump to a level be- low sublimation. And sure: clean micro-filtered solutions would help. Nickel and magnetism: you could use a demagnetizer to decrease/erase the magnetism in the shim first. Stefan Diller diller@stefan-diller.com


To clean a surface of particulates I would use replicating tape.


Tis is a cellulose acetate tape (non-adhesive) that you soſten with acetone and press down onto the surface. Let it dry and peel it off. All the particulates should come with it. I’ve had better luck in removing particulates this way compared with ultrasonics, rinses, etc. I’m not sure if an adhesive tape will work but if you don’t have replicating tape, you might try some of the tape with the “Post-it” type adhesive. It may take several applications to remove everything. Replicating tape is available from most of the EM supply houses. It comes in both a thick and thin form. Hendrik O. Colijn colijn.1@osu.edu


Particle Analysis 3DEM Listserver I prepared cryo grids for single particle analysis for 600 kD protein-


RNA complex. Te particles are overcrowded. Aſter dilution, the particles are not separated. When I diluted it further, holes became empty. Gel filtration makes a single peak, but on the grid they stick together. I have already tried glycerol, DMSO, amphipols, salt concentration 70–400 mM. None of them worked well. Te buffer contains 150 mM NaCl, 10 mM HEPES pH8, 0.5 mM EDTA, 4 mM DTT. Te sample had about 1mg/ ml, blotted for 3 sec, force 0, 100% humidity, 22C on Ultraufoil R0.6/1.0 coated with graphene-oxide. Te image was taken with a Tecnai12. Te particles are difficult to get into the holes without graphene-oxide. Any expert suggestions will be helpful. Satoru Machida dbssator@nus.edu.sg


You do not state the source of your protein-RNA complex - but


most likely, under physiological conditions, it is an “intracellular” com- plex. Which cell – prokaryotic, i.e., bacterial, or archaeal? or eukary- otic? organelles of a eukaryote? Tis is important to know. Te optimal temperature is also important to know. My suggestion is your buffer.


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