Natural light-trapping nanostructures on thermally-grown cupric oxide

Thermal oxidation of copper produces a layer of copper oxides. We present results showing that the surface of this thermal oxide naturally has an involuted morphology that can trap a very significant amount of incident radiation (similar to 70-90%). This phenomenon is of particular interest at near-infrared and visible wavelengths where the oxide shows band gap absorption. We provide details on the growth process and surface characterization data, including SEM micrographs, surface reflection spectra, as well as diffuse reflection measurements. These reveal the intricate surface morphology and its effect on light trapping and scattering from the oxide surface.