The Performance of Electron Multipliers in FIM Atom Probes

Abstract

To produce reliable results, the particle detector in the time of flight spectrometer section of the FIM atom probe must detect all the particles incident on it, and must not generate extraneous pulses which might be misinterpreted as primary events. Three detectors of the continuous dynode type—the curved Channeltron multiplier, the magnetic strip multiplier, and the parallel channel plate multiplier—were tested in an FIM atom probe using 7 keV field ionized neon atoms as the detected particles. Under normal operating conditions all three detectors exhibited some afterpulsing, which increased rapidly with increasing gain. At low gains the broadened pulse height distribution makes detection of some of the events uncertain, and a compromise must be made between afterpulsing and detection efficiency. Only the curved Channeltron could be operated at high gains with a tolerable incidence of after pulsing (<3%) by changing the potential configuration at the input end of the detector. The time between the primary pulse and the afterpulses differed for the different multipliers. With the magnetic multiplier this time interval was the longest—about 350 nsec—and thus the afterpulses could be mistakenly attributed to metal compound ions when this multiplier is used.