A computer-controlled time-of-flight atom-probe field-ion microscope for the study of defects in metals

A time-of-flight (TOF) atom-probe field-ion microscope (FIM) specifically designed for the study of defects in metals is described. This atom probe features (i) a variable-magnification internal image-intensification system based on a channel electron multiplier array for viewing the FIM image; (ii) a liquid-helium-cooled goniometer stage which allows the specimen to be maintained at a temperature anywhere in the range 13-450K; (iii) a low-energy (<or=3 keV) gas ion gun for in situ irradiations; (iv) an ultra-high-vacuum (about 4*10^-8 Pa) chamber to minimize specimen contamination; (v) a high-vacuum (about 1.33*10^-4 Pa) specimen-exchange device; (vi) a Chevron ion detector; and (vii) an eight-channel digital timer with +or-10 ns resolution for measuring the TOFS of the pulsed-field-evaporated ions. The entire process of applying the evaporation pulse to the specimen, measuring the DC and pulse voltages and analysing the TOF data is controlled by a Nova 1220 computer.