Nanowires of 3-D cross-linked gold nanoparticle assemblies behave as thermosensors on silicon substrates

In this study, we used a novel fabrication process, involving electron beam lithography and oxygen plasma treatment, to generate line and dot patterns of (3-mercaptopropyl)trioxysilane units over a large area of the Si(100) surface for gold nanoparticle (AuNP) immobilization. We synthesized the AuNPs in a two-phase system for assembly onto the Si substrate through coordination to the thiol groups of the protecting organic shell patterns. The resulting bottom layer of AuNPs was then treated with 1,6-hexanedithiol to generate thiol groups on their surfaces, thereby allowing the bottom-up construction of multiple layers of three-dimensional cross-linked AuNP assemblies, so-called poly(AuNP), linked directly to the Si substrate. We fabricated nanowires of cross-linked three-layer poly(AuNP) over large areas, with resolutions ranging from 200 nm to 10 μm. The nanowires of the poly(AuNP) underwent dramatic changes in their electrical resistivities and morphologies when melting began at a temperature of 140°C. For example, the resistivity of the nanowires assembled from three layers of poly(AuNP) at a width of 1 μm increased rapidly from 8.99 × 10^–4 to 9,471 Ω m upon increasing the temperature from room temperature to 140°C. Such microwires assembled from lines of poly(AuNP) might, therefore, be applicable as thermosensors on Si surfaces in devices miniaturized to the nanoscale.