Low work function CsI coatings for enhanced field emission properties

Thin films of cesium iodide (CsI) were deposited by pulsed laser deposition and by thermal evaporation onto Si substrates and were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and Kelvin probe measurements. The thermally evaporated films were found to be stoichiometric whereas the pulsed laser deposited films showed the presence of a Cs/CsI mixture. The latter is supported by UPS measurements whose Fermi edge indicates the presence of a metallic component (elemental Cs). The presence of a Cs/CsI mixture is also supported by the Kelvin probe work function values found to be in the range of 2.6–2.8 eV, a value in excess of the 2.1 eV reported for elemental Cs. This paper addresses the physical mechanisms responsible for the presence of the elemental Cs in the films and its ramification to their field emission properties.