The antimicrobial efficacy of silver nanoparticles (Ag NPs) modified material was generally governed by the dose of the particles or their capability to release silver ions. Here, it was found that Ag NPs acted against microbes by cooperating with tantalum oxide (TAO) in a Schottky barrier dependent manner. Size tunable Ag NPs were in situ fabricated and immobilized on TAO coating by a silver plasma immersion ion implantation process (Ag PIII). The antibacterial efficacy of these Ag NPs was reversely dependent on their size, that is large particles (similar to 20 nm) were more efficiency than small ones (similar to 10 nm) in defeating the invasion by bacteria. The result is consistent with the prediction of Schottky-Mott theory, which rectified the electron transfer nature across the interfaces between Ag NPs and the TAO substrate. (C) 2016 Elsevier B.V. All rights reserved.