Energy distribution of negative carbon ion beam extracted from a plasma-sputter-type negative ion source

The energy distributions of C- and C-2(-) beams extracted from a plasma-spu tter-type negative ion source with the concave graphite target were measure d by a retarding field energy analyzer having 1.5% resolving power. The red uction in energy spread of the energy distribution functions was observed b y adding Cs into the discharge. The observed energy spreads of C- beam for 650 V target bias were 15 eV without Cs and 13 eV with Cs, respectively. Th e shift toward the lower energy due to Cs supply was also observed. The obs erved negative energy shift was constant at about 3.7 eV for the C beam, th e value corresponded to the work function reduction from a pure graphite to Cs covered graphite surface. (C) 2000 American Institute of Physics. [S003 4-6748(00)66702-3].