Effects of a Surface Engineered Metallic Coating on Elastomeric Valve Stem Seal Leakage Page: 29
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energy of the depositant ions, which he found to be on the order of 50 -100 eV (Dini
1997). Dini also found evaporated atoms to have energy on the order of 0.1 - 0.2 eV and
sputtered atoms to have energy of about 1-10 eV. Due to gas scattering and some surface
effects, ion plating generally results in better surface coverage than vacuum evaporation
or sputter deposition (Society of Vacuum Coaters 1998). Another benefit of ion plating is
the ability to use the plasma to clean the surface of the substrate before the introduction
of the depositant. This "back sputtering" removes surface contaminants that could
interfere with the coating process (Mattox 1994).
In the case of ion plating using argon, the bombarding ions should have energies
between 50eV and 300eV. The bombarding ions should add at least an additional 20 eV
of energy per depositant atom to disrupt the columnar film growth. For example, if there
were 10 depositant atoms for every bombarding ion, each ion would need an average
energy of 200 eV. Bombarding ion energies below 50eV do not provide enough
momentum to modify the film properties. Ion energies above 300eV result in excessive
amounts of argon incorporated into the film which can cause voids and microporosity
(Society of Vacuum Coaters 1998).
Regardless of the energy level, some gas atoms will be entrapped in the film.
Depositant atoms can aggregate in the gas cloud. These aggregates form a sooty
substance that contaminates the vacuum chamber and internal components. (White 1995).
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Taylor, John Abner. Effects of a Surface Engineered Metallic Coating on Elastomeric Valve Stem Seal Leakage, thesis, December 2000; Denton, Texas. (digital.library.unt.edu/ark:/67531/metadc2690/m1/37/: accessed September 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .