SPONTANEOUS DESORPTION - A SECONDARY ION PROCESS

It is shown that kiloelectronvolt ion bombardment of a sample frequently causes electrons and/or H- ions to be sputtered simultaneously with a massive negative ion. This result is in accordance with an interpretation of the spontaneous desorption (SD) of negative ions in terms of a multistep process, the last step of which being a sputter process. It is also shown that the correlated emission of a low-mass and a massive positive ion is rather unlikely. This explains why SD spectra of positive ions are difficult to obtain with a time-of-flight mass spectrometer compared with spectra for negative ions.