Production of small doubly charged negative carbon cluster ions by sputtering.

Abstract

Carbon cluster ions with a double negative charge, and lifetimes of at least 10 \ensuremath{\mu}s, have been produced by sputtering graphite, and observed in a double-focusing mass spectrometer. Ions as small as ${\mathrm{C}}_{7}^{2\mathrm{\ensuremath{-}}}$ have been detected. The intensities of the doubly charged clusters (${\mathrm{C}}_{\mathit{n}}^{2\mathrm{\ensuremath{-}}}$ where n=7--28) follow an alternating pattern, with even-n clusters being more intense than neighboring odd-n clusters. In contrast, even-n singly charged clusters are more intense than odd n for n\ensuremath{\le}9, and less intense for n\ensuremath{\ge}13, where the clusters are believed to be cyclic.