“…28 Mainly physical vapor deposition (PVD) methods have been applied for fabricating MgF 2 thin films, e.g. thermal evaporation, [27][28][29][30][31][32][33][34][35] electron beam evaporation (EBE), 4,12,21,[36][37][38] molecular beam deposition (MBD), 33 ion beam sputtering (IBS), 31,37,39 RF-magnetron sputtering, 40 ion beam assisted deposition (IBAD), 41 and plasma ion assisted deposition (PIAD). 18,38,42 The main limitation of evaporated MgF 2 films has been that they are porous with low packing densities.…”