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 kni@caltech.edu