Basic SEM Alignment (Source Tilt, Focus, Astigmatism, Lens Alignment)

You can download the Alignment Handout (bit.ly/2OgnvDL) and SEM Concepts Handout
(bit.ly/31bAyv8). For more details on astigmatism correction: • Details of Astigmatism...
The basic idea here, as outlined in the "Alignments Handout," is to begin any alignment by correcting the source tilt (aka "crossover"), then to adjust focus, astigmatism and lens alignment in an iterative loop, and increase magnification with each loop which allows for finer adjustment of alignments. Focus not only brings your image into "good focus," it also tells you what is still wrong with the alignment; that is, it provides "visual cues" about the presence of astigmatism and lens misalignment. Put simply, if while focusing the image is stretching, you must fix astigmatism; if while focusing the image is shifting, you must fix the lens alignment. Iterate the process until the image neither stretches nor shifts while focusing, then simply settle at the right focal plane and the alignment is complete. The alignments should be done at higher magnification than the required final image. Once alignments are completed, then reduce magnification to take the desired image. The choice of alignment feature is critical for a successful alignment to clearly identify the visual cues.
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Disclaimer: This video is intended to serve as supplemental information and cannot replace in-person instrument training. Microscope operators are encouraged to consider which parameter setting is most suitable for their measurements. Caltech and KNI are not responsible for how the presented information is translated for use in other facilities.
For information or questions about this video, contact [e-mail]

[@user-kp7rr7my7r]

Thanks for the very helpful video. On my FEI Sirion system, I could not find the green X when using Crossover function, So I could not check the alignment of green X and bright dot. Could you show me how to activate the green X? Thank you very much.

[@filthamir]

Thanks! This helped me improve the image a lot.

[@youngchris5]

Thanks this was very helpful!

[@kentemmanuelsoria229]

THANKS FOR THIS VERY HELPFUL!

[@Badtzism]

Thank you a lot! I once got an introduction to our SEM and am working with EBSD every now and then, and i couldn't get a proper explaination to the lens alignment and the sigmatism and always did it by feeling and trying around without knowing to go one direction at a time, which is always a pain in the A. Is it possible to lens align on tilted samples? Because my EBSD samples are always 70° pre-tilted.

[@scottsherman5697]

Great video thanks. Do you have to correct the astigmatism after each change in current, or is it a 1 and done type of situation? Thanks

[@thekavlinanoscienceinstitu9490]

You need to correct the astigmatism after each change of voltage, current and even working distance (i.e. if you move to a new area and the focal plane has moved up or down even as little as 10s of microns, you may need to fine-tune astigmatism). So it is a constant adjustment that you have to be ready to make. The good news is that anytime you adjust focus, which you also must do very regularly, you will be able to identify if there is astigmatism by the stretching that you see or don't see. If you see it, fix it. If you don't see it, there's nothing to fix. Train yourself to recognize stretching of the image as you focus and you'll be able to diagnose the state of the alignment immediately (the same goes for identifying shifting, which indicates the need to adjust the objective lens alignment, i.e. the beam needs to be centered on the objective lens). The next step after that is to train yourself to identify focus as the place where there is stretching on either side (it could be very subtle or very severe); if you can get to that focal plane, then correcting astigmatism is as easy as adjusting the X/Y-stigmators until the image is as sharp as possible. Lastly, while correcting astigmatism, if you recognize stretching *then*, that merely means that you selected the wrong focal plane... so return to focus and try again. For more details on correcting astigmatism - and the physical mechanisms behind the correction - see this other video: kzbin.info/www/bejne/j5bYnImqZqusn5I

[@anantj18]

What do you mean by 'focus to the right' and 'focus to the left'?Does it just mean you're changing the focal plane?

[@reinarddonationo2081]

I want the handout

[@thekavlinanoscienceinstitu9490]

Sure, here is the handout for alignments: caltech.box.com/s/k2iy75hxiwkehv0ogqelz2sux9e1cs5k The latest version of all of KNI's microscopy handouts can be downloaded from this folder: caltech.box.com/s/iw6np3zzvywd7ktzkubi39k7ka08h4gv

[@thekavlinanoscienceinstitu9490]

And here is the handout for SEM Concepts: caltech.box.com/s/s8s073ywervobtf9ayc1962gypnju3uk

[@thekavlinanoscienceinstitu9490]

This handout is a guide for getting an optimal image by adjusting various beam, detector, and scan settings: caltech.box.com/s/ijd8gprg9gcavb6of5uegu7osinzsdet

[@thekavlinanoscienceinstitu9490]

Lastly, this is a handout for Ga-FIB Concepts: caltech.box.com/s/kxaxtslwol1o5a276f3lrqbhss8zvwje