Abstract: Metasurfaces utilizing conductive/dielectric patterns show great promise for manipulating and efficiently controlling electromagnetic waves. They play a vital role in THz imaging, communication, spectroscopy, and other required applications. On the other side, diamond and graphene exhibit distinct optical and electrical characteristics, and the merging of these materials holds great potential for producing lightweight, compact, and high-performance THz devices suitable for ultra-high field applications. In this work, we propose and experimentally demonstrate the synergetic effect of combining sp3 and sp2 carbon material. In particular, laser irradiation of the diamond surface leads to its graphitization, which allows us to fabricate the periodic subwavelength metall-dielectric structures. The electromagnetic response of these structures depends on both fabrication conditions and the properties of the incident electromagnetic waves. Our polycrystalline diamond films were synthesized using the plasma-enhanced chemical vapor deposition method from a hydrogen-pentane mixture activated by a microwave discharge. When diamond surface was exposed to focused laser irradiation (a 355 nm solid-state Nd: YVO4 laser source), the removal of material from the surface layer occurs. Electron microscopy, Raman and X-ray photoelectron spectroscopy study showed that the formed crater is covered with porous graphite-like material. Its depth can be controlled by adjusting the parameters of laser processing, while modifying the atmosphere allows for varying the chemical state of carbon atoms in the coating. The electromagnetic response of diamond-based metasurfaces containing engraved periodical spherical holes and parallel tracks was investigated. As experimentally shown, the transmittance through the textured diamond is reduced due to the absorption of graphite-like overlayer, and its total response depends on pattern structure. In particular, the samples with parallel tracks demonstrate linear dichroism properties. When the pattern period (p) was comparable to the wavelength (λ), several interesting features were observed in the THz spectra of these samples: (i) a dip in the spectrum for the s-polarized wave (TE-polarized light) and (ii) a peak for the p-polarized wave (TM-polarized light) were observed at the same frequency. Modeling the material properties within the framework of rigorous diffraction theory (RCWA) has allowed us to correlate these features with the coupling of surface plasmons at the dielectric/conducting interface and the waveguide mode, as well as with the effects of destructive interference. Varying the parameters of our structure (such as the thickness of the diamond film, the depth of the tracks, and the thickness of the graphite-like coating) provides broad possibilities for tuning their terahertz properties. In summary, the relative simplicity of synthesizing such metasurfaces, as well as the possibilities for their structural modification, open up additional prospects for designing a new generation of THz photonics elements based on them.

Cite: Sedelnikova O.V. , Gorodetskiy D.V. , Paddubskaya A.G. , Valynets N.I. , Bulusheva L.G. , Okotrub A.V.
Sp3-sp2 THz metasurfaces based on laser-treated diamond
The 8th International Workshop on Electromagnetic Properties of Novel Materials 26-30 Aug 2024