Modeling Electrical Transport in Random Networks Composed of Metal-Oxide Nanowires: The Transition from Junction-Dominated to Nanowire-Dominated Regime

Random networks of metal oxide nanowires are of great technological interest in a variety of applications. Unveiling how the properties of the elementary components of the network, namely, nanowires and nanowire-nanowire junctions, may emerge as macroscopic functionalities is a fundamental issue. However, the disordered nature of the network and difficulties in estimating important properties, such as the junction contact radius, hinder the understanding and exploitation of these materials. This paper develops a model suitable for discussing the electrical resistance of the network and its transition from the junction-dominated regime to the nanowire-dominated regime, based on the nanowire characteristic lengths and energies. The result is achieved by integrating recent network theories with the equations of semiconducting metal oxides. Constraints imposed by the thermodynamics of contact mechanics are introduced to provide a lower limit for the unknown junction contact radius. Focusing on the literature of gas sensing, the model provides a theoretical background to frame the relationship between gas-sensing properties and the surface termination of nanowires in the context of network theories.