Ion Microprobe Mass Analyzer

This paper describes the development of an instrument which is analogous to an electron microprobe x-ray analyzer, whereby the electron microprobe is replaced by an ion microprobe, and the x-ray spectrometer by a mass spectrometer. A duoplasmatron is the primary ion source. The primary ion beam is mass separated to eliminate impurity ions. A probe diameter of less than 2 μ at 2×10−10 A is realized for 12-kV Ar+ ions. A new mass spectrometer was developed with the emphasis on high transmission, yet simple construction. It is stigmatic imaging, double focusing, has a mass-resolving power of 300 with a solid acceptance angle of 1.5×10−2 sr (4° half-angle) and a transmitted-energy bandwidth of 10%. It consists of an axially symmetrical electrostatic Einzel lens, a 45° spherical condenser sector, and a magnetic field with plane but inclined pole faces, which deflects the beam by 90°. No entrance slit is used. Experimental results are presented.