| 摘要 |
An electron beam aperture element (10) comprises a body (11) provided with a passage (12) for an electron beam (E) and with a blocking surface (15) for blocking travel of part or all of the beam otherwise than through the passage. The blocking surface (15) is angled to cause departing electrons derived from the blocked beam or part thereof to be directed away from the axis (13) of the passage and, in particular, into an electron trap cavity (21) bounded by the surface (15) and a wall of a screening member (17). The wall returns electrons to the blocking surface (15) for redirection back into the cavity (21), thus preventing escape of scattered electrons or delaying their escape until sufficient absorption has taken place to render them largely harmless to the interior environment of an electron beam column equipped with the element.
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