Dear EBSD/SEM community,
I could very much use your help with regard to a problem that I have:
I am trying to record EBSD patterns while I work in immersion mode (FEI Nova Nanolab), hence with a magnetic field extending to the sample. I do agree that making EBSD compatible with immersion does not seem like a top priority, since there is usually no point in having a 1-2nm probe size when the interaction volume is 50-100nm-ish anyway. However, (at least) two techniques could very much benefit from this compatibility, Transmission Kikuchi Diffraction, clearly, but also a technique that I recently developed (1).
I read in the litterature (there is not much on it though), that the pattern get distorted + shifted, which can be corrected (2).
I would already be very happy with distorted patterns, that would be a start, but for some reason I don’t get any…
Accroding to the pattern without background substraction (see slide enclosed), it seems that just no BSE electrons reach the detector. My guess is that the magnetic field is too strong, and that most BSE are “spiraled away” from the detector.
Does any of you have any advice/experience/insight on this compatibility? Or a test that can be conducted?
Thank you for your time!
Etienne Brodu
(1) Brodu et al., Determination of the structure and orientation of nanometer-sized precipitates in matrix materials via transmission diffraction signals emitted by bulk samples in the Scanning Electron Microscope, 2020
(2) Chou et al., A Method for the Correction of EBSPs Distorted by Lens Magnetic Fields, 2013
I have never worked with immersion mode.
Does it insert smaller aperture or changes the beam current when you turn immersion mode?
You can try going to WD ~20 mm, the magnetic field infuence may be smaller when you are further from pole piece, also 30 kV beam should be less affected by magnetic field than 20 kV.
What exactly is the benefit of immersion mode? Does it really significantly decrease the spot size? I am thinking that SEMs without immersion mode usually have ~1-2 nm resolution, and with immersion this might be half of that. I wonder if this ~1 nm improvement helps you with TKD...
Thank you Grzegorz and Tijmen I appreciate your help,
To answer your questions:
Grzegorz, the aperture stays the same while you switch from field-free to immersion. I am not sure that the intensity remains the same though, which is why I also tried with large apertures in immersion, with lots of current (clearly visible from the high S/N ratio in immersion SE images). Intensity is not the issue.
In terms of WD, you cannot work at large WD. Immersion cannot extend the field and hence properly focus if the WD is typically larger than 7mm. And I also tried at 30keV, with no improvement.
Tijmen, an immersion lens system can offer a field-free mode and magnetic-field immersion mode, but the performance in the field-free mode is no better than that of a pinhole lens. In immersion mode the probe size is 1-2nm and images are stunning, especially STEM in SEM images (BF, DF, HAADF). but without the magnetic field (field-free), the resolution is quite poor, more in the 5-10nm range. Hybrid lenses in that sense are better, I guess, at least when it comes to diffraction.
I add a slide about TKD + immersion mode (previous image was in EBSD mode).
I find it quite puzzling. That being said this problem is rather specific and maybe not so many people work with that type of lens. Thanks anyway.
FYI: someone told me at a conference that with the same microscope, in immersion mode, very nice TKD patterns could be obtained with an on-axis camera (OPTIMUS by Bruker), although quite distorted, but which can be corrected. I believe it has something to do with electron direction relative to the magnetic field direction. I also asked FEI and EDAX for their opinion on that and can keep you and the community posted.
Best,
Etienne
Interesting Etienne, I am puzzled by the TKD pattern you show with Immersion, it doesn’t seem to be a small distortion... How do the patterns look after distortion, and how can one know the distortion is accurately removed?
- Badges
- Science method