A 75-keV electron beam with a low angular divergence (8×${10}^{-6\mathrm{}}$ rad) combined with a Wien filter spectrometer is used to examine the dispersion of radiative surface plasmons in thin oxidized aluminum films. The measurements agree with theory, provided the effect of the oxide layer is included.

• Received 5 September 1973

DOI:https://doi.org/10.1103/PhysRevLett.31.1487