Transient Self-Heating at Nanowire Junctions in Silver Nanowire Network Conductors

Abstract

Nanostructured transparent conducting electrodes (TCEs) may be suitable replacements for transparent conductive oxides due to their optical, electrical, and mechanical properties. Because nanowire (NW) nanowire or tube–tube junctions are the transport bottlenecks in network-based conductors, understanding the properties of these junctions and their connectivity within the network is crucial to understanding and controlling electrical conduction through these networks. Quantifying local self-heating within the network can provide information on the coupled electrothermal response, local conduction pathways, and potential reliability. In this study, self-heating thermal transients within a silver NW network are characterized using high-resolution transient thermoreflectance imaging that provides high temporal (∼200 ns) and spatial (∼200 nm) resolution. The self-heating induced by an applied voltage pulse results in distinct temperature changes at microscopic hotspots formed at individual NW–NW junctions. For both heating and cooling cycles, thermal time constants less than $\text{1 }\mu {\text{s}}$ are observed at various hotspots. For a representative hotspot, line scans along two crossing NWs, taken at different time instants ranging from 0 to 2 μ s, show the temporal and spatial evolution of the temperature profile. We estimate the van der Waals force (∼−4.0244 N), contact width (∼5 nm), and interface thermal resistance (∼1.6 × 105 K/W) between NWs and the underlying substrate. A heat transfer model that considers local power generated at a hotspot, local coupling between the NWs and substrate, heat conduction along the NWs and heat transfer into the substrate, is developed and used to interpret the experimental data. The heat transfer model and experimental temperature profile help to quantify the local power generated at the hotspot and the fraction of this power propagating along each wire. The ability to resolve the local self-heating with such temporal and spatial resolution uniquely enables understanding of electrothermal response and current pathways in the distributed conductors.