A polarized helium ion beam for surface electronic structure studies
Harrison, Allen Ray
Walters, G. King
Master of Arts
This thesis describes the development of a spinpolarized He+ ion beam suitable for use as a- probe of surface electronic structure of metals. The method would represent an extension of ion neutralization spectroscopy (INS), and should provide new information on surface magnetism, electron correlation effects, and the dynamics of the ion neutralization process. Production of the polarized helium ion beam involves optically pumping helium metastable atoms in an rf electric discharge with subsequent extraction of ions created by metastable-metastable collisions. The principles of this technique and details of the experimental apparatus are presented. Ion currents of up to 1~ A were attained and optical pumping absorption measurements suggest a beam polarization of 8 to 1%. For a moderately low beam energy, about 15 eV, an ion density at the target surface of roughly 2 X 1 A-cm- with an energy spread of about 3 eV was attained. A specific experiment is proposed in which the polarized He+ beam would be used to probe the surface magnetic properties of nickel.