Temperature-dependent work functions of free alkali-metal nanoparticles

Abstract
Photoionization yields have been measured as a function of temperature for the alkali metals Li, Na, and K in the form of free nanometer-sized clusters in a beam. The data can be fitted very well by a finite-temperature Fowler plot, originally derived for bulk surfaces. The resulting temperature-dependent ionization thresholds match precisely the literature work function values and are, within the experimental uncertainties, in agreement with recent theoretical models for thermal shifts of the work function.