Femtosecond laser treatments to tailor the optical properties of hafnium carbide for solar applications

HfC-based materials are promising composites for application as solar absorbers. Being a ceramic with some metallic character, HfC shows intrinsic spectral selectivity, but quite a high reflectance at the wavelengths of the Sun spectrum. In this work, a femtosecond laser treatment has been specifically tailored to increase the solar absorbance of a composite 70 vol% HfC-30 vol%MoSi2. We investigated the morphological surface changes induced by the femtosecond laser on both phases, proposing a mechanism for surface modifications on the basis of microstructural analysis. Despite the presence of two ceramic phases with different physical properties, the laser was able to modify both phases simultaneously upon specific parameters. The effect of the surface texturing on the optical spectrum was analyzed. By use of specific laser interaction and patterning parameters, the formation of a regular surface pattern allowed the absorbance-over-emittance ratio to be increased from about 1.8 to 2.1.