SECONDARY-NEUTRAL MICROPROBE WITH ELECTRON-GAS POST-IONIZATION

The essential features and the performance data of a recently developed secondary-neutral microprobe are described which interfaces the well-established technique of electron gas (plasma) post-ionization with a high-transmission magnetic sector mass spectrometer. Small-area analysis is accomplished by means of a separate high-brightness liquid-metal (Ga+) ion source. For 20 keV Ga+ ions and 1 nA beam current the intensities of post-ionized sputtered neutrals amount to some 10(3) counts/s for pure elements, and secondary neutral micrographs can be acquired with an image resolution in the mum range. Due to the high transmission of the mass spectrometer secondary-neutral intensities up to 10(9) counts/s per 1 mA primary current can be obtained in the direct bombardment mode (i.e., by extracting the sputtering beam out of the plasma), thus extending the detection limit down to the 10 ppb regime. Furthermore, the instrument can be operated at high mass resolution (M/DELTAM = 9500) providing the option of isotope analysis by means of secondary-neutral mass spectrometry.