TIME FOCUSING IN A FIELD PULSED ATOM-PROBE WITH A REFLECTRON

Abstract

The poor termination of a tip in the discharge line of an atom-probe and the field ionization of the species at different times during the voltage pulse cause a broadening in the kinetic energy of the ions, thus deteriorating the ToF-spectra. To improve the resolution of the atom-probe, the Poschenrieder-filter was introduced quite early. Despite the elaborate designs so far in use, the simpler design of a reflectron, as is commonly in use with other ToF-techniques, was never tried in this context. To test this idea, a reflectron with an acceptance angle of 1.5° for a 0.8 m ToF-length was constructed. The time focusing is of first order (as with a Poschenrieder filter), which gives an improvement at an assumed ΔE/E = 10 % from Δt/t = 0.05 to Δt/t = 0.001 with compensation. The instrument was tested with a field pulsed atom-probe and an improvement of m/Δm from ~30 to > 400 was achieved.