Effect of reactive gas additives on surface morphology evolution of stainless steel substrate undergoing low energy Ar ion bombardment

• We investigate surface of stainless steel substrates after plasma ion sputtering.
• Roughness (Ra) increases after ion sputtering from 2 nm to 38 nm with Ar gas plasma.
• Addition of 1% dry air to the Ar reduces roughening from 38 nm to 4 nm.
• AES profiling of the substrates shows significant difference for Ar and Ar/air cases.
• Chemically active gases can be used for roughness control during ion sputtering.

In many cases surface ion bombardment results in roughening of metal's and alloy's surfaces. In the present study, a phenomenon of surface roughening inhibition during the ion bombardment is presented. The phenomenon occurred during the plasma extracted ion sputter etching at normal incidence with 400 eV positive ions, when 1% of dried air was added into the plasma forming Ar gas. Two 18%Cr–10%Ni mechanically polished to about 2 nm average roughness (Ra) stainless steel test pieces were sputter etched with and without the air additive. The roughening was inhibited to Ra ≈ 4 nm, which was about 9.5 times lower than that of the sputtered without air additive (Ra ≈ 38 nm). The phenomenon is discussed in terms of chemisorption of active plasma species introduced by the air additive and competing roughening/smoothening mechanisms.