Development of spin-polarized ion scattering spectroscopy

Spin-polarized ion scattering spectroscopy using an electron-spin-polari zed He-4(+) ion beam was developed as a novel analytical method of the element selective spin state at outermost surfaces. Spin-polarized He+ ions were generated from the Penning ionization of metastable He 2(3)S(1) atoms (He*), which were spin-polarized by optical pumping (OP). The spin polarization of He* (P-He*) was observed to be the highest with an OP radiation density of about 0.05 W cm(-2), and a further increase of the OP radiation density reduced P-He*. This decrease of P-He* is attributed to imperfect polarization of the OP radiation, hence optimization of the OP radiation density is essential to obtain He+ ions with high spin polarization. As a result of this optimization, we successfully observed the spin dependence of the scattered He+ ion yield on an Fe(100) surface exposed to an oxygen atmosphere.