Spin-polarized electron tunneling: The importance of the potential barrier shape

Aspects concerning the shape of the potential barrier for the tunneling of spin-polarized electrons through a vacuum are discussed, and STM measurements indicating that the spin polarization increases with decreasing potential barrier thickness are presented. Model calculations of the potential barrier allow critical parameters of the potential barrier to be determined, namely the height φB and the position zm of the energy maximum. Variations in these parameters correlate with the magnitude of the tunneling electron spin polarization.