Development of Spin-Polarized Ion Scattering Spectroscopy

Abstract

Spin-polarized ion scattering spectroscopy using an electron-spin-polarized ⁴He⁺ 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 2³S₁ 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 PHe* 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.