Sputtering negative carbon ions from cesiated graphite surfaces

The sputtering of negative carbon ions from graphite targets bombarded with Cs⁺ ions has been studied. The energy of the Cs⁺ ions has been varied from 200 V to 20 kV. The targets studied were polycrystalline, pyrolytic and vitreous graphite. The negative ion yield strongly depends on the amount of cesium adsorbed on the surface and intercalated into the bulk of the graphite. The optimum C⁻ ion yield is 0.5 to 0.6 C⁻ ions per incident Cs⁺ ions for a bombarding energy of 10 keV and for a target temperature of 200 °C. The yield is independent of the graphite structure. In addition to C⁻ ions, negatively charged clusters of carbon ions up to C⁻₁₉ were sputtered from polycrystalline and pyrolytic graphite. Sputtering from vitreous graphite produces only light clusters, up to C⁻₄.