Spin-dependent electron excitation and emission in the neutralization of He+ ions at paramagnetic surfaces

The interaction of He+ ions with surfaces has been widely used as a tool to probe different properties of the surface. There are recent experiments that measure the spin polarization of electrons emitted during the neutralization of spin polarized He+ ions impinging on the Al(0 0 1), Au(0 0 1) and Cu(0 0 1) surfaces. The experimental results show that (i) the spin polarization of the total emitted electron yield is about 30% for the three surfaces, being the preferable spin state that of the electron bound to the He+ ion and (ii) the spin polarization of electrons emitted at higher energies is high (around 70% for Al(0 0 1) and 50% for Au(0 0 1) and Cu(0 0 1)) but decreases as electrons with lower energies are included. Here, we apply our local model to understand in a quantitative way these measurements. First, we calculate the energy distribution of electrons excited in the Auger neutralization of a He+ ion. Next, we describe the transport and escape of these excited electrons to obtain the energy distribution of emitted electrons. The theoretical results allow us to explain the similarities and the differences found in these surfaces.