Photoionization Spectroscopy of Lithium, Sodium and Potassium Nanoparticles in a Beam for the Metallic Work Function

Abstract

We have used a modified particle source with a temperature controllednozzle to measure the temperature dependence of the work function forLithium, Sodium and Potassium. The temperature dependence of thework function arises from thermal expansion of the metal whichresulted in a decrease of the electron density and a concomitant changeof the Fermi energy. We have shown that photoionisation spectroscopyof Lithium, Sodium and Potassium nanoparticles in a beam providehigh accuracy data for the metallic work function and its temperaturedependence. The influence of temperature on the photoionizationspectra of smaller clusters where thermal expansion has been predictedto have a stronger effect than in bulk and of particles composed ofmaterials which exhibit measurable changes in the work function andphotoyield at the melting point