SECONDARY-NEUTRAL MICROPROBE WITH ELECTRON-GAS POST-IONIZATION

The essential features and the performance data of a recently develope d 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 analy sis is accomplished by means of a separate high-brightness liquid-meta l (Ga+) ion source. For 20 keV Ga+ ions and 1 nA beam current the inte nsities of post-ionized sputtered neutrals amount to some 10(3) counts /s for pure elements, and secondary neutral micrographs can be acquire d with an image resolution in the mum range. Due to the high transmiss ion of the mass spectrometer secondary-neutral intensities up to 10(9) counts/s per 1 mA primary current can be obtained in the direct bomba rdment mode (i.e., by extracting the sputtering beam out of the plasma ), thus extending the detection limit down to the 10 ppb regime. Furth ermore, the instrument can be operated at high mass resolution (M/DELT AM = 9500) providing the option of isotope analysis by means of second ary-neutral mass spectrometry.