I need to clean the hydrocarbon contamination on the carbon substrate of TEM grid.
However, I heard that substrate could be broken by the powerful plasma.
My substrate is pure carbon, with ~3nm, ~5nm, and ~10nm.
The cleaner which I plan to use is GATAN Solarus Plasma Cleaner.
So, which gas is prefer to use? Ar? O2? H2? I heard that use the mixed gas, but which mixture is prefer?
And how long do I need to expose them under plasma?
Soo Ik Park
Not sure I understand this part:
'My substrate is pure carbon, with ~3nm, ~5nm, and ~10nm'
And why are you not simply using new TEM substrates? They're designed to be single use. Please explain.
In the LCD and semiconductor industry I used oxygen plasma etching for cleaning organic residues especially polyimides. These were very effective and very mild. 10 minutes was usually fine for layers up to the 500 nm region.
In days of ESCA/XPS I used Ar+ ion etching to remove atomic layers. I would not recommend this for what you want to do.
I suppose you have a sputter coater which is capable of reversing polarity ("etch", :"clean" and such), and you need to make your grids hydrophilic. In empty coater switch polarity and find a voltage which is low but still produce a stable discharge. For the next run place some grids (carbon side up) and "clean" them just for a few minutes (1-4). Check if they are hydrophilic now and you may want to check them with TEM for possible damage (never saw any damage myself).
I think you will find the answer on the following website:
Article Downstream Plasma Technology for Cleaning TEM Samples on Carbon Films
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If this is the first-gen Solarus (if I remember correctly) the plasma-cleaning procedure is done only by radicals, as the TEM holder itself is shielded by a metal shield towards direct plasma (please check this by looking into the chamber when opened). If this is the case, the "plasma-cleaning" by recipe will work only if you have your TEM grid in the TEM holder while cleaning (and it will etch your amorphous support grid if you just put them in the chamber, unshielded).
From memory: factory setting for carbon-supported TEM grids (to make them hydrophilic) is a low power (2W from RF source, I believe), running H2/O2 mixture, for 10-20 s.
PS there are several on-line guidelines that worked for the authors, worth checking:
- (H/O plasma, basically from the Gatan catalogue) https://analyticalscience.wiley.com/do/10.1002/micro.144
- (O/Ar plasma): https://iubemc.sitehost.iu.edu/Documents/ProtoChips_C_FlatGrids_1.pdf
- (several different mixtures described): Chapter Specimen Preparation for High-Resolution Cryo-EM
If I read this correctly, you are looking to prevent the build-up of the "black squares" during imaging, which occurs when mobile hydrocarbons are cross-linked by the electron beam. This coats your sample and kills imaging. It doesn't sound like you are looking to make the grid hydrophilic, right?
Aref Wazwaz above makes a reference to the downstream plasma cleaner from ibss Group. This can indeed be used to clean TEM grids. I did a report for ibss Group a few years back, using a hydrogen plasma. This works well. Oxygen plasma, while good at attacking hydrocarbons, will also perforate your carbon membrane. In our report we showed that grids often come from the manufacturer with residual hydrocarbons on them. You should be able to do the same with your Solarus.
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