During a discussion with an oxford instruments sales person regarding the installation of the new CMOS based symmetry EBSD detector for our SEM, he mentioned that the optimum working distance possible to get the pattern center in our SEM geometry is 17.8 mm. Does this mean that once installed I cannot run the EBSD scans with shorter working distance ranging from 10 mm to 15 mm?
Sherin Bhassyvasantha The pattern center is the point of intersection on the phosphor screen of the ray in the horizontal direction the sample and normal to the plane where the electron beam meets the sample. It is crucial for obtaining accurate indexing of your patterns (apart from crystal structure at first) and needs to be calibrated as per your SEM geometry.
Generally speaking, smaller working distance can be used for mapping, but would require re-calibrating your pattern center. This can be done automatically (if vendor software has the provision for it) or manually (in a mode with more functionalities than a normal user, something like an engineer mode).
It is best to contact the vendor for the same, as they know the geometry of your SEM thoroughly.
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