Variation in nanopillar surface on plasma-etched stainless steel owing to the crystal phase and composition

Abstract

Argon (Ar) plasma etching of stainless steel leads to the formation of nanopillars that function as an antibacterial surface. This study investigated the influences of the crystal phase and composition of steel on nanopillar characteristics, aiming to produce an effective antibacterial surface. Nanopillars on the ferritic stainless steel surface with a body-centered cubic (BCC) structure showed a higher number density, compared with the austenitic case with a face-centered cubic structure. In addition, the number density of the pillars decreased in the cases of lower C and higher Cr contents of the stainless steel. Such differences were dominated by the behavior of carbide precipitation, which acted as a template for etching. Stainless steels with BCC structures and a low Cr content are advantageous for carbide formation; in contrast, a low C content is a disadvantage for the formation of nanopillars owing to the absence of a carbide source. The nanopillar surfaces exhibited antibacterial activity against the gram-positive Staphylococcus epidermidis species, but the effect was mitigated for stainless steel with a reduced number density. The crystal structure and chemical composition of stainless steels influence their antibacterial activity; hence, plasma etching conditions must be optimized for stainless steel to produce an effective antibacterial surface.