(a) Due to the electric field at the interface, moving electrons feel an effective magnetic field and consequently electrons are spin-polarized. (b) Spin-polarized positrons are implanted in a sample under the application of a direct current. From current-reversal asymmetry of the intensity of annihilation γ-rays from surface positronium, the spin polarization of surface electrons is determined. Incident positron energy is adjusted by a deceleration tube.