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

Marco Girolami,Matteo Mastellone,Tilde De Caro,Veronica Valentini,Elisa Sani,Alessandro Bellucci,Daniele M Trucchi,Valerio Serpente,Riccardo Polini,Stefano Orlando

doi:10.3390/ma13245761

Abstract

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 interact with visible and infrared light. As a result, native transparent diamond turns into a completely different material, namely “black” diamond, with outstanding absorptance properties in the solar radiation 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 workflow of black diamond, we demonstrate that it is possible to ensure the same optical properties as those 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 the combined 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 optical properties of black diamond films are not comparable to those of their UHV-fabricated counterparts.

Highlights

In the field of concentrated solar energy conversion, black diamond is gaining increasing attention, thanks to its outstanding solar absorptance values, even exceeding 90% [1,2,3], as well as for its suitability for operation at very high temperatures in thermionic emission-based devices [4,5,6]
The results of the morphological, structural, and optical characterization of the three black diamond samples (TM1, TM2, TM3) fabricated under different gas environments will be introduced and compared to those previously reported on their ultra-high vacuum (UHV)-fabricated counterparts [2,3]
Morphology can be highlighted among the samples treated under a compressed air (Figure 2a), a N2 (Figure 2c), or a He (Figure 2e) flow: in all cases, well-formed and rather regular LIPSS can be noticed, with a periodicity, Λ, of about 170 ± 10 nm, which perfectly matches the theoretical value of 166 nm given by the relationship Λ = λfs /2n, where n = 2.41 is the refractive index of diamond at the laser wavelength λfs = 800 nm used for the treatments [29]

Summary

Introduction

In the field of concentrated solar energy conversion, black diamond is gaining increasing attention, thanks to its outstanding solar absorptance values, even exceeding 90% [1,2,3], as well as for its suitability for operation at very high temperatures in thermionic emission-based devices [4,5,6]. Periodic Surface Structures [7]) able to strongly enhance the interaction between material and sunlight. Even if LIPSS can been successfully obtained with nanosecond (ns) [8] laser pulses, the use of ultrafast pulse duration regimes, such as picosecond (ps) or, even better, femtosecond (fs), allows for a more precise control of LIPSS geometry, because thermal effects are significantly reduced. Lots of research activities have been reported on LIPSS, which represent a versatile and practical way to functionalize the surface of metals [9,10,11,12,13], dielectrics [14,15,16] and semiconductors [17,18,19]. LIPSS allows for an accurate control of the physical and/or chemical properties of the laser-treated materials.

Methods

Results

Conclusion