Thermal transport in ZnO nanocrystal networks synthesized by nonthermal plasma

Semiconductor materials with independently controlled electrical and thermal properties have a unique promise for energy-related applications from thermoelectrics and thermophotovoltaics. Here, using nonthermal plasma synthesized, direct-contact zinc oxide (ZnO) nanocrystal (NC) networks infilled with amorphous Al2O3, and amorphous ZnO-Al2O3 mixture, it is shown that such independent control of electrical and thermal properties is achievable. In this study, in addition to our early reports on control of the electrical properties in these two-phase nanocomposites by tailoring the contact radius between NCs, we demonstrate that the infill composition has a significant impact on the overall thermal conductivity of the NC network and can be used for thermal control. It is also shown that in these heterogeneous systems, the phonons are the dominant heat carriers, and the NC-NC contact radius has a negligible effect on thermal transport. The work suggests that this paradigm of independently controlling the electrical and thermal properties of NC-based materials through tuning the NC-NC contact radius and infill composition can be exploited even further by varying NC and infill materials with potential applications ranging from solar cells and light emitting diodes to solid-state energy converters.