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IMS 6f-7f

Technical note

POSTACC - Post acceleration system

The ion / electron conversion efficiency of thefirst dynode of the Electron Multiplier varies with the velocity of the impinging secondary particles. post acceleration system for the ElectronMultiplier has therefore been developed in order to improve the performance of the detectionsystem of CAMECA IMS instruments. The higher the velocity the higher theElectron Multiplier detection quantum efficiency (DQE). When the first dynode of theElectron Multiplier is grounded, like on standard CAMECA IMS instruments, the velocity of secondary particles is fixed by both their massand the secondary accelerating voltage. Thus, when low extraction voltages have to beused (in-depth profiling at very high depth resolution), the sensitivity of the instrument is reduced because of the decrease of the Electron Multiplier yield due to lower impact energy on the secondary particle onto the first dynode. This loss in Electron Multiplier performance canbe eliminated by

Post acceleration system:Specifications

post-accelerating thesecondary particles

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Post acceleration voltage adjustable from -10 to + 8kV just before they reach thefirst dynode. Moreover, at given secondaryextraction voltage, a post-acceleration mini- mizes the mass dependence of the Electron Multiplier efficiency. A

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EM yield > 80% for mass species

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Electron Multiplier parameters computer controlled

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Pulse height distribution measurement capability