and silicone protects o-rings well. It’s not so sticky. No need to worry about super-high vacuum in this application? Mark Cannell February 5, 2019 Correct, the vacuum is not the issue, but Fomblin and the

like are still good greases, just pricey. Tey don’t outgas, and so won’t get gunk on the optics or otherwise contaminate the optics. I don’t think the silicone high-vacuum greases are good for lubricating. First, they give off acetic acid vapor; I don’t see why Dow would recommend it for optical components. Sec- ond, the silicone greases are sticky. Not good for moving parts. It does protect o-rings, but watch the acetic acid and o-ring composition. Silicone grease seals coverslips well, though. Phil Oshel February 5, 2019 No acetic acid from the Dow corning stuff I’ve used—it’s a

specialty silicon polymer plus thickener, not polymerized “bath- room caulk,” as far as I know. It’s more like low-MW Sylgard, I think. While its exact composition may be a trade secret, its vapor pressure is very low at 100°C, so I doubt it could be outgassing much, if any, acetic acid. I’ve not seen it corroding brass parts. Mark Cannell February 5, 2019 I’m guessing you DON’T mean Dow Corning 732, as that

is the one that has acetic acid. As Phil clarified, there is “vac- uum grease,” and then there is “grease for use in a vacuum.” Tey are not quite the same thing. Vacuum application servo lubricant grease is safe (grease for use in a vacuum), whereas the Dow Corning 732 is actually meant for creating a seal in a vacuum chamber, etc. and can off-gas. Craig Brideau craig. February 5, 2019 732 is certainly not high-vacuum grease! Here is a spec

sheet for Dow Corning high-vacuum grease: https://www. Mark Cannell February 5, 2019

Microscopy Listerver preparation of cross-sectioned TEM samples of metal I’m working with a student who has metal samples with

an ∼1 μm thick layer of amorphous silicon oxynitride on the surface, and they want to prepare cross-section TEM samples. We have tried gluing the sample sandwich together with Epo- Tek 353ND (also known as Gatan G1) and MBond 610, and both stacks fell apart on cutting. I assumed that the SiON lay- ers were delaminating, but a visual inspection using the optical

microscope convinced me this was not likely the underlying cause of the problem. Both epoxies used were not expired and were cured according to the manufacturer’s cure schedule. I have had no issues with cross sections of other sample systems and these exact same epoxies, so I wonder if we need to use a differ- ent epoxy chemistry than these standards. Does anyone have expe- rience with the SiON sample system? Is there a better epoxy to use, like Araldite? We would like to try to create a sample stack before giving up and switching to attempting tripod/wedge polishing. Christopher Winkler January 23, 2019 I have summarized the replies I received regarding this

issue below:

1. “Since the SiON is ∼1 μm thick, top monolayers probably do not matter. I can suggest trying the following: 1. Plasma clean the sample just before applying epoxy. We are using 4–5 min. of pure Ar at 50W forward RF with range 5W in our Gatan Solarus plasma cleaner. Or, 2. Sputter ∼1–2 nm of Cr or Fe on the top surface before applying epoxy. We use Gatan PECS to do that. If Fe or Cr targets are not available in your lab, sput- tering with any reactive metal available should also work.”

2. Many are concerned the film is delaminating from the metal substrate. We should probably check this using the SEM, but we don’t see any evidence of delamination in the optical microscope (when comparing the failed glue specimens with pristine specimens).

3. Many suggested FIB. Te student prefers a conventional TEM sample preparation to generate a larger electron trans- parent region than the FIB would provide, but if all else fails then we can fall back to the FIB.

4. “A simple suggestion that, perhaps, might work (this is how we work): Why don’t you inverse the order of operations? I mean:

first, cut the small pieces and then glue them as a sandwich. Hopefully, the glued pieces will hold together during the grinding steps. Good luck with the ion milling aſterwards.”

5. “I have used Devcon 5-minute epoxy for many years on all sorts of samples with success. It is much more viscous than the other usual TEM epoxies, but you know the sample is ready for the next step in 5 minutes.” Christopher Winkler January 25, 2019



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