Black Nickel Coating as a Broadband Terahertz to Deep-Ultraviolet Absorber.

Broadband absorbers capable of attenuating electromagnetic radiation from terahertz (THz) to deep-ultraviolet (DUV) frequencies are critical components in spectroscopy, imaging, sensor technology, and energy harvesting systems. However, most conventional absorbers are limited by their narrow operational bandwidth and often require complex or costly nanostructuring. In this study, we present a black nickel (b-Ni) coating fabricated via scalable electrodeposition onto copper substrates, followed by controlled acid etching, as a cost-effective and robust broadband absorber. The resulting b-Ni films, characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), demonstrate ultrabroadband absorption spanning from 30 to 1500 THz, with absorptivity exceeding 95% throughout this range. Compared to nanostructured metamaterials and moth-eye analogs, the b-Ni coating offers significant advantages in fabrication simplicity and scalability. This work positions chemically etched b-Ni coatings as a highly promising material for large-area applications in spectral and imaging instrumentation, including emerging systems operating within the THz frequency range.