Ion assistance effects on electron beam deposited MgF2 films, Alvisi, Marco, de Tomasi F., A. Patria Della, Di Giulio M., Masetti E., Perrone M.R., Protopapa Maria Lucia, and Tepore A. , Journal of Vacuum Science and Technology, Part A: Vacuum, Surfaces and Films, Volume 20, Number 3, p.714-720, (2002)