Abstract
We produced free beams of cold nanometer-sized particles of lithium, sodium and potassium and measured the three corresponding photo-ionization yield curves. Quadratic (Fowler) plots, originally developed for bulk surfaces, were found to provide a good fit to the threshold shape and were used to obtain the particle ionization potentials. The latter match precisely the bulk work functions cited in the literature, suggesting that photo-ionization of free nanoclusters may form a useful complement to traditional photoelectron studies of surfaces. Within 0.25–1 eV above the threshold, the ionization efficiency begins to drop. This effect, which has parallels in bulk-surface and small-cluster photoemission, is presently not well understood but may be related to an interplay between electron emission and collective surface plasma excitations.
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