Electrical Resistance in a Composite of Ultra-Small Silver Nanoparticles Embedded in Gold Nanostructures: Implications for Interface-Enabled Functionality

Abstract

Ultrasmall nanoparticles of noble metals, in particular silver (Ag) or gold (Au), have been extensively investigated for their optical, magnetic, chemical, and physical properties, but assembling such structures in an electrically conducting metallic matrix, where the physical dimension of individual nanoparticles plays a decisive role, has remained elusive. This is because true metallic conduction through individual or clusters of metallic nanoparticles is often prevented by tunnel barriers due to surface-protecting ligands, oxidation, etc. By removing the chemical remnants, these challenges have been overcome in a cross-linked nanohybrid assembly made of ultrasmall silver nanoparticles (AgNPs) in an all-metallic matrix of Au. The resulting Ag–Au nanohybrid exhibits metallic behavior where the resistance decreases with decreasing temperature, for all radii (rAg ≫ 1–3 nm) and concentrations of AgNPs (average center-to-center distance between two AgNPs d ≈ 4–6 nm) from room to cryogenic temperatures (≈ 6 K). Strikingly, we observe the electrical resistivity of the hybrid to scale directly with the net surface area of the embedded AgNPs, thereby achieving residual resistivity as high as 40 μΩ.m, which is more than 2 orders of magnitude larger than that of crystalline Au. Our experiment outlines a novel method of designing metals with nanostructured interfaces that can lead to new phenomena and functionality.