Conductive Networks of Plasma-Synthesized Zinc Oxide Nanocrystals

Abstract

Many envisioned applications of semiconductor nanocrystals (NCs)—such as flexible transparent conductors and thermoelectric generators—require high electrical conductivity, σ, across an NC network. In this dissertation I explore methods for increasing σ of networks of plasma-synthesized ZnO NCs, and I discuss the evolution of the networks’ optical and electronic properties across three orders of magnitude of σ. Primarily I examine their localized surface plasmon resonance and interparticle electron transport mechanism. σ is determined by the free electron density, n, and the interparticle contact radius, ρ, which I modulate by impurity doping, photodoping, photonic sintering, and surface modification via atomic layer deposition. At large n and ρ, an insulator-metal transition occurs, and σ becomes comparable to typical values for dense, large-grain polycrystalline ZnO films. Near the transition I compare the measured values of n and ρ and the observed transport behavior to theoretical predictions. Additionally, I evaluate potential technological applications of ZnO NC networks and present routes toward scalable production.