As an emerging flexible thermoelectric
material, polymer composites with embedded carbon nanotube (CNT) networks
have shown promising properties, but their thermoelectric transport
has not been fully understood. Herein, we embedded CNT networks in
poly(dimethylsiloxane) (PDMS) elastomers and analyzed their thermoelectric
properties using Landauer theory. We find that the simultaneous increase
in Seebeck coefficient and electrical conductivity with increasing
CNT content up to ∼40% can be attributed to the tunneling transport
at CNT junctions with the gap distance decreasing with increasing
CNT content. Beyond 40% CNTs, both properties are reduced and saturated
due to the reduced PDMS content and increased material nonuniformity,
which effectively replaced the PDMS gap with an air gap at the junction
with a higher barrier to reduce the properties. Our results and analysis
provide important insights into the material optimization of hybrid
thermoelectric composites based on CNT networks and many other nanoscale
fillers.
Considerable advances in manipulating heat flow in solids have been made through the innovation of artificial thermal structures such as thermal diodes, camouflages, and cloaks. Such thermal devices can be readily constructed only at the macroscale by mechanically assembling different materials with distinct values of thermal conductivity. Here, we extend these concepts to the microscale by demonstrating a monolithic material structure on which nearly arbitrary microscale thermal metamaterial patterns can be written and programmed. It is based on a single, suspended silicon membrane whose thermal conductivity is locally, continuously, and reversibly engineered over a wide range (between 2 and 65 W/m·K) and with fine spatial resolution (10−100 nm) by focused ion irradiation. Our thermal cloak demonstration shows how ion-write microthermotics can be used as a lithography-free platform to create thermal metamaterials that control heat flow at the microscale.
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