LOW-ENERGY, ELECTRON-SPIN-POLARIZED HE-4(-SOURCE() ION)

A source of low-energy, electron-spin-polarized He-4(+) ions based on an optically pumped, rf-excited helium discharge is described. Ion pol arizations P+ of similar to 0.13 are achieved at beam currents of simi lar to 0.1 nA, decreasing to similar to 0.09 at currents of similar to 0.5 nA. Ion beam energies as low as 10 eV have been realized, with an energy spread of less than or similar to 3 eV full width half maximum . The ion polarization can be reversed (P+-->P+) simply by changing th e sense of circular polarization of the optical pumping radiation. The source is suitable for use in a wide variety of applications includin g surface physics studies. (C) 1998 American Institute of Physics.