MORPHOLOGY OF NOVEL ANTIMICROBIAL SILVER FILMS DEPOSITED BY MAGNETRON SPUTTERING S.B. Sant 1 , K.S. Gill 2 and R.E. Burrell 3 1 Veeco Technology Center, San Jose, CA 95119, USA 2 National Research Council of Canada, Edmonton, Alberta, Canada T6G 2G8 and 3 Westaim Corporation, Fort Saskatchewan, Alberta, Canada T8L 3W4 (Received June 18, 1999) (Accepted in revised form September 3, 1999) Keywords: Silver; Sputtering; Thin films; Anti-microbial behaviour; Nano-crystalline 1. Introduction Prevention and treatment of microbial infections is widely carried out using silver salts, however, it is also known that simple silver ions from these salts are easily rendered inactive by reaction and complexation with biofluids [1]. Consequently, the practical usefulness of these conventional formu- lations is severely limited because they are unable to provide prolonged release. The bioactivity of silver can be enhanced by thermal, mechanical, chemical or electrical stimulation [2,3]. However, the suitability of each of these methods for mammalian applications has not been convincing because of inherent practical problems. This opportunity has resulted in the development of a novel metallic silver film capable of providing unassisted sustained release of metal ions at antimicrobial concentrations when in contact with aqueous electrolytes [4,5]. This efficacious, inexpensive antimicrobial coating, formed by a physical vapour deposition (PVD) process, viz. magnetron sputtering, provides sustained release of antimicrobial agent at therapeutically active levels; is applicable to a wide variety of devices and materials; has a useful shelf life; and has low mammalian toxicity. The role of microstructure, dopants and their interplay in antimicrobial activity is a new field of science. The precise mechanism of silver release from metallic surfaces in aqueous media is still unclear, especially under cases when the surface has not been pre-activated with stimuli. However, the microstructural characterization of nanocrystalline silver films may provide us a clue to explain the biological activity of silver films produced under a given set of deposition conditions. The sputtered silver films described in this investigation were previously studied using X-ray photoelectron spec- troscopy (XPS) [6] and high-resolution transmission electron microscopy (HRTEM) with in-situ heating capability [7]. HRTEM studies showed that the biologically active nanocrystalline films had a very fine grain size, of the order of 15 nm, with a high density of growth twins whose incoherent twin boundaries intersected grain boundaries. Annealing the films above 140°C lead to grain growth and a loss in biological activity [7]. Moreover, in active films, XPS results indicated that the oxygen species existed in a number of different chemical states [6]. Thus, the objective of the present study was to characterize the morphology of novel bioactive PVD silver films to demonstrate their usefulness as antimicrobially active coatings. Pergamon Scripta Materialia, Vol. 41, No. 12, pp. 1333–1339, 1999 Elsevier Science Ltd Copyright © 1999 Acta Metallurgica Inc. Printed in the USA. All rights reserved. 1359-6462/99/$–see front matter PII S1359-6462(99)00294-8 1333