Pellin, Michael J.; Lykke, Keith R. & Lill, Thorsten B. Focused Ion beam source method and Apparatus, patent, August 17, 1998; (https://digital.library.unt.edu/ark:/67531/metadc717041/m1/1/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .