Engineering optical properties of silver nanoparticles for broadband absorbing metasurfaces based on a lithography-free process

Abstract

Constructing ultrafine nanogaps is of crucial importance in realizing significant localized-field enhancement (so called “hot spot”). In this paper, we demonstrated a lithography-free broadband absorbing metasurface consisting of Ag nanoparticles with ultrafine nanogaps fabricated using the laser shock technique incorporated with the thermal-annealing technique. Experimental results and numerical simulations demonstrated that horizontally compressed Ag nanoparticles possessed smaller nanogaps for high sensitivity, uniformity, and stability. Laser shock of metallic nanoparticles showed a strong size effect and pressure dependency. The absorption of the broadband absorbing surfaces reached nearly 94 %, leading to excellent reliability for Raman detection. Furthermore, this novel substrate with different colors exhibited insensitivity to the incident or observation angle in an ambient environment and promising practical applications in many all-angle color filters and biomimetic photonic structures.