Electrodeposited 3D Tungsten Photonic Crystals with Enhanced Thermal Stability

Tungsten inverse opal photonic crystals were fabricated using a template directed electrodeposition method. The electrodeposition was accomplished using a molten salt solution at elevated temperatures. Following template removal, the tungsten inverse opals were conformally coated with hafnia or alumina via atomic layer deposition. This surface passivation layer increased the thermal stability of the tungsten microarchitectures by limiting surface diffusion. Alumina protected tungsten inverse opals were thermally stable up to 1000 degrees C for at least 12 h in forming gas (5% H-2 in Ar). Hafnia protected inverse opals were thermally stable up to 1400 degrees C for at least 12 h in forming gas. We expect that this surface passivation technique can also be implemented to increase the thermal stability of other refractory metal microarchitectures. The demonstrated thermal stability is an important property for the realization of metallic photonic crystals as narrow band emitters for thermophotovoltaics.