Evidence for a Quantum Size Effect of the Conduction Electrons during Oxidation of Cs

The transition from Cs to ${\mathrm{Cs}}_{11}$ ${\mathrm{O}}_3$ leads to a twofold increase of the intensity of electron emission from the valence band (and to a substantial decrease of the emission from the $\mathrm{Cs} 5p$-core levels) as probed by metastable deexcitation spectroscopy, although the concentration of conduction electrons is reduced by about 50%. This phenomenon is attributed to a quantum size effect of the conduction electrons as proposed in a theory by Burt and Heine.