Fabrication of carbon/refractory metal nanocomposites as thermally stable metallic photonic crystals

Abstract

Metallic photonic crystals (MPhCs), three-dimensionally nanostructured metals, have been previously investigated as efficient emitters for thermophotovoltaic conversion of solar energy and waste heat into electricity. However, the thermal stability of these nanoscaled structures is limited at high temperatures. Here we present a fabrication scheme for preparing metal-coated carbon inverse opal photonic crystal structures that may be useful for thermal emission modification. Three-dimensionally ordered macroporous (3DOM) carbon films and monoliths, which can maintain their structure up to at least 2200 °C in argon, were used as thermally stable scaffolds for chemical vapor deposition (CVD) of the refractory metals tungsten, molybdenum, or tantalum, all with a thin hafnia interlayer. The tungsten-coated photonic crystals were found to be stable after heat treatment at 1000 °C for at least five hours, under high vacuum (10⁻⁶ torr). The thermal stability of these nanocomposite materials is mainly limited by the adhesion of the refractory metals on the 3DOM carbon scaffold. The hafnia interlayer serves as an adhesion promoter for this material, and structures without a hafnia coating show metal agglomeration after heat treatment at 1000 °C, as demonstrated with millimetre-sized 3DOM carbon monoliths that were only partially coated with hafnia. These results can have important implications not only for the development of efficient thermophotovoltaic emitters, but also for fabrication of other thermally stable, functional nanocomposite materials.