Photoionization spectroscopy of lithium, sodium and potassium nanoparticles in a beam for the metallic work function

We have used a modified particle source with a temperature controlled nozzle to measure the temperature dependence of the work function for Lithium, Sodium and Potassium. The temperature dependence of the work function arises from thermal expansion of the metal which resulted in a decrease of the electron density and a concomitant change of the Fermi energy. We have shown that photoionisation spectroscopy of Lithium, Sodium and Potassium nanoparticles in a beam provide high accuracy data for the metallic work function and its temperature dependence. The influence of temperature on the photoionization spectra of smaller clusters where thermal expansion has been predicted to have a stronger effect than in bulk and of particles composed of materials which exhibit measurable changes in the work function and photoyield at the melting point.