Beam Showering
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Procedures of Beam Showering
There are no standardized conditions for beam showering, and every operator has his or her preferred recipe.
1. Ensure all cameras are retracted to avoid damages.
2. Ensure the Ronchigram button is turned ON.
3. Ensure the setting is at the default values: Probe size = 8C, cameral length = 8cm, Mag = 1Mx
4. Strongly Underfocus the electron beam by turning the Obj knob anti-clockwise (Defocus = -2um).
Ensure that the electron beam is as large as possible while without having any distortion on the fluorescent screen.
The electron beam is concentrated on the samples for beam showering when it is underfocused.
5. Open all the apertures, especially the CL1 and CL2.
This allows the sample to expose to the beam directly.
6. Control >> Free Lens Control >> Set the current of CL 1 to "3000" >> ON
The beam becomes brighter than before after clicking "ON".
7. Insert OL Lower = aperture #4 and SA = aperture #4
Although the fluorescence screen can stop the beam, it could be damaged by the bright beam as well.
The inserted apertures are to block the electron beam.
8. Wait for 5 min of beam showering.
Note: If the contamination is not effectively frozen, repeat the beam showering for another 5 min.
9. After beam showering, resume to the previous setting:
>>> Off the CL1 = 3000,
>>> Retract OL lower aperture and SA aperture
>>> Insert CL1 aperture #1
>>> Double click the "STD Focus" button
10. Examine if the beam showering effectively clean the contaminants.
11. Check the A1 and B2 aberration, this beam showering process re-induces aberrations.
Beam Showering
Mechanism: An extremely thin carbon layer is formed or can be cracked; the contaminants are polymerized and immobilized locally temporarily. The beam showering effect is restricted by time as contaminants diffuse back after a short while.
The last line of defense: Other methods should be used to remove the thick contaminant first; beam showering is the last step to treat the residual contaminant as it does not remove the contamination.
Contamination causes aberration calibration very challenging because the Ronchigram will disappear soon due to the continuous deposition of the carbon-based layer. . If the electron beam has severe 3-fold aberration, you can see the triangular shape of stains after zooming out. Beam showering for 5 min can mitigate the contamination issue.
Cooling
Cooling is highly recommended for beam-sensitive materials.
Examples: monolayer 2D Materials, polymers, ionic crystals, and hydrated species.The overall approach used will depend on the specimen, the nature of the contaminant, etc.
Case 1: Low volatility residues on inert samples
Such as long-chain solvents (ethylene glycol ), a thick layer of surfactants (thick CTAB), oils
Plasma Cleaning >> Beam Showering
Case 2: Volatile residues on inert samples
Such as acetone residual, a thin layer of surfactant
Baking >> Plasma Cleaning >> Beam Showering
Case 3: Beam Sensitive Materials
Such as ionic/hydrated crystal & polymer etc.
Cooling is universally effective for all types of contaminants.
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