Scanning Microscopy


Microchannel plate (MCP) electron detectors compare favorably with the Everhart-Thornley detector for producing SEM images from both secondary and back-scattered electrons. The MCP is a compact array of 105 - 106 channel electron multipliers with a gain in excess of 106 and the collective ability to count ~ 108 electrons per second. The MCP can be mounted coaxially with the beam allowing un-tilted sample orientation and electron collection into a large, field-free solid angle. The speed and low noise of the MCP allow images to be made in less than one second at moderate beam currents or in longer times with very low beam currents. Because of the wide detection angle, images from coaxially located MCP's show little loss of detail due to shadowing but by the same token are peculiarly "flat" in appearance. This suggests that they might usefully complement another detector in many applications. Lifetime data are still limited, but the detectors used for this report show no noticeable deterioration with well over 100 hours of use.

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