Origin of surface-induced visible light absorption of nanostructured diamond

Abstract Surface nanotextured diamond, named “black diamond,” absorbs efficiently visible light. This feature allows this material to be used in solar devices, such as the p/i/n photocathode under study in this work. Using optical and x-ray surface-sensitive spectroscopy techniques, this study establishes a correlation between the material’s optical properties and its chemical structure to elucidate the nature of light absorption and photocarriers’ generation. The analysis reveals that the surface states in the very first atomic layer of the diamond, such as carbon sp 2 reconstruction states and carbon oxygen bounds at 1.25 and 2.5 eV with respect to the maximum of the valence band, respectively, are the key factors for the enhancement of the visible light absorption with respect to pristine samples. These defects, together with a collective effect induced by the diffraction light trapping, could be useful for using black diamond in solar applications by exploiting the increase in the visible light absorption. Impact statement Diamond, an ultrawide bandgap semiconductor with an energy bandgap of 5. 47 eV, possesses exceptional thermal, mechanical, and electronic properties, making it a promising material for a wide range of applications. However, its intrinsic nature renders diamond natively visible blind, limiting its potential in solar-energy applications. Surface texturing using ultrashort laser pulses offers a way to enable diamond’s utilization in sunlight conversion. Nonetheless, it is crucial to understand the effects induced by laser treatments on its surface to tailor and optimize it as an active solar material. This study highlights the critical role of sp 2 defects formed in the uppermost layers of monodimensional laser-induced periodic surface structures (1D LIPSSs). These defects play a primary role in absorbing subbandgap photons. The recognition of the direct involvement of surface defects in the absorption mechanism paves the way for the development of highly efficient and fine- tuned nanotextured surfaces, designed to maximize the presence of these beneficial defects. Graphical abstract