Physical vapour deposition of metallic lithium

The preparation of thin films of LiF was resumed at the European Commission-Joint Research Centre-Institute for Reference Materials and Measurements (EC-JRC-IRMM) few years ago. Deposits of 6LiF for cross-section measurements and 7LiF for neutron production via the Li(p,n) reaction with an areal density up to ~600 μg cm−2 are prepared by physical vapour deposition. In order to reach high neutron yields, a larger number of lithium nuclei per unit surface is required. In a proton beam, interaction with fluorine results in high-energetic gamma-rays which can interfere with experiments making use of gamma spectrometry. In this regard, the deposition of metallic lithium by means of physical vapour deposition up to an areal density of 300 μg cm−2 was examined. Yet, metallic lithium is known to diffuse into certain materials and reacts with atmospheric air by forming several reaction products. Therefore, the effect of a passivation layer on the substrate and protective covers of Au or LiF on the metallic Li layer (sandwiches), deposited by means of a multi-crucible evaporation system, and the stability of the layers when irradiated with a proton beam were investigated.