Indirect tunneling conductivity of periodic arrays of isolated gold nanoparticles

Ordered arrays of gold (Au) nanoparticles (NP) exhibit tunable plasmonic properties that enhance detection capabilities in next generation sensors. Arrays of Au NPs with 100nm periodicity and diameters ranging from 55nm to 75nm were fabricated by a sequential solid-state dewetting technique. The array ordering and the NP sizes were influenced by the AAO membrane geometry and the thickness of the evaporated film. Using a polymer-based technique, the arrays were transferred onto various substrates for a study of their optical and electronic properties. Absorption measurements of NP arrays on sapphire substrates showed that the larger NP size (reduced interparticle spacing) resulted in a red shift of the plasmon resonant wavelength from 550nm to 575nm, with peak height and width depending on the areal NP coverage. For a study of their electronic properties, the arrays were transferred onto Si/SiO₂ substrates, where a weak tunneling dc current was measured. At the interparticle spacing of tens of nm, the applied voltage is orders of magnitude less than that required for the direct particle-to-particle quantum tunneling. In contrast, devices constructed with arrays on sapphire substrates without Si layer showed no tunneling current, indicating that the Si substrate used for the SiO₂ films plays a crucial role in electron conductivity through the array of insulated Au NPs. The origin of this current will be assessed in the context of several potentially contributing field-assisted transport mechanisms, including: Landau–Zener tunneling, Poole–Frenkel emission, Fowler–Nordheim tunneling, Shottkey emission tunneling, and trap-assisted tunneling. The observed room temperature electron transport across relatively large distances through a dielectric and the possibility of manipulating electromagnetic absorption with plasmonics are promising for the future of nanoelectronics.