Magnetron-sputtered Ag surfaces. New evidence for the nature of the ag ions intervening in bacterial inactivation.

DC-magnetron sputtering with an Ag target on textile surfaces produced Ag particles with sizes approximately 4.7 nm (+/-15%). Sputtering for 15 s led to Ag layers of 15-20 nm. The threshold sputtering time precluding airborne bacterial growth was about 60 s. In this case, the coating was approximately 40-50 nm thick and the cotton Ag loading was 0.0026 wt %. The Ag particle size did not vary significantly with sputtering time between 15 and 600 s. Only coatings above this thickness lead to bacterial inactivation. Ag/Pt targets with sputtering times<60 s did not increase the bactericide performance of the Ag cotton samples with respect to sputtering from an Ag target alone, as expected from the position of Pt respect to Ag in the electrochemical series (Galvanic effect). The Ag cotton deposition led to very thin metallic semitransparent gray color coatings. X-ray of the Ag cotton suggested the presence of amorphous and crystalline Ag species. By X-ray photoelectron spectroscopy (XPS), it was found that the amount of oxidized silver species on the cotton was similar for sputtering times of 60 and 600 s, but the total amount of Ag deposited was almost two times higher after 600 s sputtering. This suggests that the positive silver-ions were located mainly at the silver interface. The type of silver ions produced using the Ag/Pt sputtering was determined to be very similar at 15, 60, and 600 s with the silver ions produced with the Ag target. This explains the lack of an increased inhibitory effect of Pt during the inactivation of airborne bacteria when present in the Pt/Ag target with respect to the Ag target, because in both cases similar silver ionic species were found.