Hot-electron scattering length by measurement of spin polarization

Abstract

A new method of determining the hot-electron scattering length $l$ is provided by the measurement of the spin of photoemitted electrons from a thin film on a substrate of dissimilar electron-spin polarization (ESP). Results have been obtained for Ni, $l={10.8}_{-1.7\mathrm{}}^{+2.5\mathrm{}}$ Å for electrons 5.4 ± 0.3 eV above $E_F$, and for Cu, $l={10.0}_{-1.7\mathrm{}}^{+2.6\mathrm{}}$ Å for electrons 5.2 ± 0.5 eV above $E_F$. The agreement between our result for Ni and measurements where electrons were "marked" by their kinetic energy rather than spin indicates the absence of any thickness-dependent depolarization mechanism in the photoemission process. A nonzero ESP is observed in very thin Ni films showing that ferromagnetism occurs already in films of one or two layers average thickness. The similarity between $l$ for Cu and Ni is unexpected in terms of the random-$k$ approximation and points out the importance of the scattering-matrix elements.