Effect of Perforation on the Sensing Properties of Monolayer-Capped Metallic Nanoparticle Films

We report on the effect of perforation within a monolayer-capped metallic nanoparticle (MCNP) film on sensing of volatile organic compounds (VOCs) and water molecules. Our results show that continuous MCNP film exhibits positive responses on exposure to VOCs and to water, consistent with the swelling and dielectric sensing mechanisms. In contrast, perforated films exhibit positive responses on exposure to VOCs but a high-magnitude negative response on exposure to high levels of water. The negative responses were higher by at least 1 order of magnitude compared with the positive responses. The results are explained in terms of ionization of condensed water and/or SiO2 sites in MCNP-free domains under applied voltage, side-by-side with the tunneling mechanism within the MCNP domains. The controlled morphology afforded by MCNP assemblies, combined with the existence of multiple sensing mechanisms under real-world humidity conditions, would enable a host of new fundamental and applied opportunities.