Full-Plane Threshold Energies for Cathode Sputtering of Metals with Ar+ Ions

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Abstract
Full‐plane threshold energies at normal ion incidence of Ar+ ions have been determined for sixteen metals with a method of ``detection of deposits,'' using demountable sputtering tubes of different designs. Since in each case the target, immersed like a Langmuir probe in a high‐density plasma, was bombarded by singly charged ions with a high ion current density under background conditions similar to those in Hg+‐ion sputtering tubes used for the determination of thresholds, the threshold data obtained for Ar+‐ion bombardment are comparable to those formerly published for sputtering with Hg+ ions. This comparison discloses that threshold predictions for Ar+ ions, formerly made by simply exchanging the mass of the Ar+ ion for the mass of the Hg+ ion in a threshold formula, are not correct at all. This result also implies that threshold formulas in which the interaction between the target atom and the impinging ion is only expressed by a mass factor containing the masses of the target atom and of the ion are not adequate to cover simultaneously the thresholds for different kinds of ions. The threshold data can be represented by a calculable factor f′. Applying the simplified threshold formula of the authors' theory of cathode sputtering to the thresholds measured with Ar+ ions, another representation of the data is possible by the dissipation factors δAr+ which are different from those for sputtering of the same metals with Hg+ ions, indicating that the energy loss due to Debye waves during sputtering is different for different bombarding ions. The thresholds for Ar+‐ion sputtering are, in general, lower than those for Hg+‐ion bombardment; however, they obey the same law of periodicity seen in a plot vs atomic number, as formerly established by the author for sputtering with Hg+ ions.