Optical absorption and heat conduction control in high aspect ratio silicon nanostructures for photothermal heating applications

•Geometrical dependences of photothermal conversions were studied experimentally and numerically for periodic hole and pillar nano-arrays made of silicon.•Effective thermal conductivities were defined for periodic nano-arrays that are extremely anisotropic.•A guideline was proposed to design periodic nanostructures which can efficiently increase surface temperature by photothermal heating. In photothermal heating, the temperature increase observed in an irradiated material is dependent on its optical absorption and thermal conductivity. A wide variety of studies have shown that optical absorption can be tailored using various nanostructures, including metamaterials, plasmonic structures, photonic crystals, and surface texturing. Similarly, thermal conductivity can be also tuned by nanostructures, including phononic crystals and superlattices. However, few have examined the potential for the simultaneous control of optical absorption and heat conduction to optimize photothermal heating processes. In this study, silicon hole and pillar arrays are tailored for their optical adsorption and thermal conductivity by varying their geometrical parameters. Subsequent experiments and numerical simulations reveal that the thermal conductivity of the nanostructures has a stronger influence on the photothermal heating effect than their optical absorption. Pillar arrays show a larger photothermal heating effect than the hole arrays; nevertheless, hole arrays are advantageous where connectivity is required, as in photothermal detector applications. With this understanding of the relationship between nanostructure dimensions and their photothermal properties, this analysis may guide the future design of periodic nanostructures for photothermal heating applications. [Display omitted]