Differentially-pumped low-energy ion-beam system for an ultra-high vacuum (uhv) atom-probe field-ion microscope. Report No. 4017

A differentially-pumped low-energy (50 to 3000 eV) ion-beam system for the in-situ irradiation of specimens in an uhv atom-probe field-ion microscope (FIM) was designed and constructed. The ion-beam system consists of a Finkelstein-type ion-source, an Einzel lens and a magnetic mass-aanalyzer. The ion source is connected to the analyzer chamber by small apertures which results in differential pumping between the ion source and the nalyzer chamber; during a typical in-situ irradiation of a specimen the pressure in the atom-probe is approx. 10-7 Torr. The ion-current density is approx. 0.5 μA cm-2 for 300 eV (He4)+ ions at the atom-probe FIM specimen; ion current-densities as high as (2 to 3) mA cm-2 have been achieved for an ion-beam energy greater than or equal to 1 keV. Therefore the irradiation of a specimen with a single-mass, mono-energetic ion-beam is accomplished with the complete elimination of a long pump-down time after the irradiation