Nanoscale-Thick Silver Black Films Fabricated in He/Ar Inert Gas Conditions for Broadband Absorbers

Broadband light absorbers are attractive for their applications in photodetection and photothermic conversion. Metal black absorbers are highly nanoscale porous deposits in the presence of inert gas and exhibit nanoscale structure. Silver nanoparticles have attracted intensive research interest because of their distinctive electrical and optical properties. Here, we fabricated a number of silver black films with nanoscale thicknesses under various gas ambient atmospheres (He and Ar). Our aim is to fabricate broadband absorbers with high absorption performance from the visible-to-mid-IR (MIR) spectral range and investigate their aging behaviors. The He-ambient silver black film exhibited average absorption coefficients of 3.17, 2.27, and 1.81 μm^-1in the visible, near-IR (NIR), and MIR ranges, respectively, with the highest value of 6.50 μm^-1at a wavelength of 357 nm. Those of the Ar-ambient film were 0.48, 0.51, and 0.443 μm^-1in visible, NIR, and MIR ranges, respectively. The absorption coefficients of the He-ambient film were much higher than those of the Ar-ambient film, which were very promising candidates as broadband absorbers. Moreover, metal black films suffered from aging phenomena because of their nanoscale porous structure. The long-term stability of the optical properties was worthy of attention for applications. Therefore, the room temperature aging behaviors of nanoscale-thick silver black films were investigated. Comparative analyses of the atomic content before/after aging demonstrated that the aging was attributed to crystallization, deliquescence, and oxidation. Comparative analyses of the absorption and photothermal response characteristics before/after aging were also performed. The results demonstrated that the nanoscale-thick silver black films possessed great absorption stability in the visible-to-MIR range and photothermal response stability, which can provide valuable reference for applications of broadband absorbers such as IR dynamic scene generation.