The assignee ranking is led by instrument OEMs and semiconductor-equipment firms alongside several university systems, with the University of California appearing repeatedly in co-assignee pairs. Filing activity from the largest named assignees has dropped to zero in the most recent year, which reflects both the roughly 18-month publication lag and a genuine multi-year slowdown. No single assignee holds a dominant share of the 661 families in this corpus, so the field reads as competitively distributed rather than concentrated in one company's hands.

Filing volume peaked in 2018 at 54 records, eased to 31 by the 2022 midpoint, and has continued to soften into the most recent partial year. That pattern is consistent with a field where the foundational instrument and sample-preparation claims were largely filed in the 2017-2019 window. New filings now are more likely to be refinements on established techniques than entirely new approaches, though the most recent year's low count is partly an artefact of publication delay rather than a sudden stop.

H01J, covering electron and discharge tubes, and G01N, covering material analysis and testing, together account for the bulk of the 661-family corpus. Image processing under G06T, scanning-probe measurement under G01Q and semiconductor-device applications under H01L each have a smaller but real presence. Optics, dimensional measurement and photolithography subclasses carry comparatively few filings, suggesting those intersections are less contested.

That filing, from Hitachi High-Tech Corporation, covers a specific standard-sample construction used to calibrate TEM, EDS and EELS elemental mapping — a layered structure of heavy-atom crystalline films around a thin light-atom amorphous layer. It does not block elemental mapping methods generally; it blocks calibration approaches that rely on this particular layered heavy-atom/light-atom sample architecture. Developers working on different calibration standards, or on mapping methods that don't depend on a physical reference sample of this design, sit outside its claims.

The thinnest IPC subclasses in this dataset — G03F photolithography, G01B dimensional measurement and G01Q scanning-probe — each carry well under 50 records against the 491 and 362 seen in the core H01J and G01N subclasses. That gap suggests under-claimed territory at the boundary between electron microscopy and these adjacent measurement disciplines, particularly for hybrid inspection methods that combine electron-beam imaging with scanning-probe or lithography-linked metrology.