title: A differentially pumped low-energy ion beam system for an ultrahigh-vacuum atom-probe field-ion microscope.
abstract: An ultrahigh-vacuum (UHV) differentially pumped low-energy (50-3000 eV) ion beam system for the in situ irradiation of specimens in a UHV atom-probe field-ion microscope (FIM) was designed and constructed. The ion beam system consisted of a Finkelstein-type ion source, an Einzel lens, and a magnetic mass analyzer. The ion source was connected to the analyzer chamber by small apertures which resulted in differential pumping between the ion source and the analyzer chamber; during a typical in situ irradiation of a specimen in the atom-probe FIM the total pressure was maintained at approximately 10(-7) Torr. In the case of helium ion irradiation the optimum ion-current density was approximately 0.5 microA cm(-2) for 300-eV He+ ions at the atom-probe FIM specimen. After the completion of a helium ion irradiation the pumpdown time from 5 x 10(-7) to approximately 3 x 10(-10) Torr in the atom-probe FIM chamber was 0.5 h.
authors.affiliation: Department of Materials Science and Engineering and the Materials Science Center, Bard Hall, Cornell University, Ithaca, New York 14853, USA.
authors.forename: J
authors.initials: J
authors.lastname: Amano
authors.forename: D N
authors.initials: DN
authors.lastname: Seidman