Femtosecond-Laser Nanostructuring of Black Diamond Films under Different Gas Environments

Irradiation of diamond with femtosecond (fs) laser pulses in ultra-high vacuum (UHV)conditions results in the formation of surface periodic nanostructures able to strongly interactwith visible and infrared light. As a result, native transparent diamond turns into a completelydifferent material, namely "black" diamond, with outstanding absorptance properties in the solarradiation wavelength range, which can be efficiently exploited in innovative solar energy converters.Of course, even if extremely effective, the use of UHV strongly complicates the fabrication process.In this work, in order to pave the way to an easier and more cost-effective manufacturing workflowof black diamond, we demonstrate that it is possible to ensure the same optical properties asthose of UHV-fabricated films by performing an fs-laser nanostructuring at ambient conditions(i.e., room temperature and atmospheric pressure) under a constant He flow, as inferred from thecombined use of scanning electron microscopy, Raman spectroscopy, and spectrophotometry analysis.Conversely, if the laser treatment is performed under a compressed air flow, or a N2 flow, the opticalproperties of black diamond films are not comparable to those of their UHV-fabricated counterparts.