Emission of Ions from Solids.

The emission of negative ions and electrons from solids has been investigated. H('-) ions have been produced by two different processes, sputtering and backscattering. The sputtering of H('-) ions was achieved by using high-energy Cs('+) ions to bombard a metal hydride target. The target was on the cathode of an approximately planar high -voltage diode. Several metal hydrides were investigated but the best results were obtained when using a CsH target. An important parameter is the H('-) ions sputtered per Cs('+) ion incident on the target. Maximum H('-) ion yields of 0.4 were achieved using 10kV Cs('+) ions in pulses of up to 1-ms duration. H('-) ion current densities of up to 50 mA cm('-2) were obtained when operating the diode in the pulsed regime. In addition to ions, electrons were unavoidably sputtered with maximum yields of about 2. The effects of incident ion mass and target composition on the sputtered H('-) ion yields were investigated. The sputtering of other negative ions, particularly Au('-) and O('-), was observed. The composition of various targets was determined using SIMS analysis. A theoretical model for the sputtering of H(' -) ions has been considered. There are some similarities between the experimental results and the theoretical predictions, but the numerical values of the e('-) and H('-) ion yields have not been explained. H('-) ions were also produced when thermal H atoms were incident on a cesium surface, a process referred to in the literature as backscattering. The most important parameter for this process is the H('-) ion efficiency, defined as the number of H('-) ions produced per incident H atom. The maximum H('-) ion efficiencies were 1.5 x 10('-4) and were obtained using H atoms from a 2500(DEGREES)K tungsten oven. Unavoidably, electrons were also produced with efficiencies of about 0.02. For the backscattering efficiencies of H('-) ions, a theoretical model considered by Hiskes is discussed. Good agreement for the H('-) ion efficiencies is obtained, but the theoretical model does not predict the production of e('-).