Ultrafine tuning of the metal volume fraction in silver/silicate nanocomposites near the percolation threshold†
Metal dielectric nanocomposites exhibit a broad range of physical properties that can be tuned by varying the metallic volume fraction (ϕ), in particular near the percolation threshold. The study and exploitation of the so-called critical properties at this threshold are currently limited by the inability to finely tune ϕ in a continuous way, for example in physical mixtures. Here we present a novel chemical fabrication process for metal dielectric coatings consisting of TiO2 nanoparticles dispersed in a mesoporous silver silicate host matrix. UV light irradiation of these active films allows for the photocatalytic formation of silver nanoparticles with a dose dependent, measured incremental variation in ϕ as small as 0.01% up to a total volume fraction of 20% (i.e. exceeding the 3D percolation threshold). Moreover, this is achieved in situ, that is to say, while measuring the optical or electrical properties of the nanocomposite. Simple examples of hysteretic resistance measurements and optical absorption/reflection as a function of ϕ are presented, demonstrating the utility of this nanocomposite system for the study of percolation phenomena as well as its potential for applications such as sensitive strain sensors.