The Role of Amorphous Nanocrystalline Carbon Films in Interference on Flexible Copper Foils

The ultrathin amorphous nanocrystalline carbon (a-C) layers deposited onto flexible copper foils are an alternative to reduce reflectance. Several problems like high melting energy and the enhanced reflection of pure Cu can be solved when using a-C films. Reflectance measurements were performed at normal incidence from near-ultraviolet to near-infrared. The experimental results are compared to a model based on multilayer propagation. It is found that a-C coating with suitable nanoscale thickness critically reduces Cu reflectance due to destructive interference and losses. Results can reach up to 80% reduction for specific a-C ultrathin films. This represents the minimum reflectance points (MR) varying as a function of wavelength. The thickness of MR varied from 25 to 65 nm in the range of this work. Sources of divergences between the model and the measurements include the substrate roughness and the unusual reflectance growth of Cu for shorter wavelengths. Raman spectroscopy confirmed the presence of nanocrystalline graphite in the a-C films potentialy improving absorption. a-C films are eco-friendly and lightweight, suitable for scalable process deposition. It is applicable for absorbing energy purposes such as laser.