Comprehensive characterization of broadband ultralow reflectance of a porous nickel-phosphorus black surface by numerical simulation.

Porous nickel-phosphorus (NiP) black surfaces exhibit excellent low reflectance in the visible and near-IR regions. Through use of a model of the surface morphology and composition, the reflectance was numerically simulated by a three-dimensional finite-difference time-domain method to determine the origin of the low reflectance. In agreement with experimental results, the simulations showed a spectrally flat, quite low reflectance of <0.1% over the entire visible-near-IR region under certain conditions. The reflectance depended strongly on the thickness of the black nickel oxide layer and the aspect ratio of the three-dimensional surface morphology. A method of validating the reflectance of porous NiP black surfaces is suggested.