Optical-phonon states of SiC small particles studied by Raman scattering and infrared absorption

Helium Ion-Assisted Wet Etching of Silicon Carbide with Extremely Low Roughness for High-Quality Nanofabrication

Silicon carbide (SiC) is a promising material for a wide range of applications, including mechanical nano-resonators, quantum photonics, and non-linear photonics. However, its chemical inertness poses challenges for etching in terms of resolution and smoothness. Herein, a novel approach known as helium ion-bombardment-enhanced etching (HIBEE) is presented to achieve high-quality SiC etching. The HIBEE technique utilizes a focused helium ion beam with a typical ion energy of 30 keV to disrupt the crystal lattices of SiC, thus enabling wet etching using hydrofluoric acids and hydrogen peroxide. The etching mechanism is verified via simulations and characterization. The use of a sub-nanometer beam spot of focused helium ions ensures fabrication resolution, and the resulting etched surface exhibits an extremely low roughness of ≈0.9 nm. One of the advantages of the HIBEE technique is that it does not require resist spin-coating and development processes, thus enabling the production of nanostructures on irregular SiC surfaces, such as suspended structures and sidewalls. Additionally, the unique interaction volume of helium ions with substrates enables the one-step fabrication of suspended nanobeam structures directly from bulk substrates. The HIBEE technique is expected to facilitate and accelerate the prototyping of high-quality SiC devices.

Structural and Optical Properties of Silicon Carbide Powders Synthesized from Organosilane Using High-Temperature High-Pressure Method

The development of new strategies for the mass synthesis of SiC nanocrystals with high structure perfection and narrow particle size distribution remains in demand for high-tech applications. In this work, the size-controllable synthesis of the SiC 3C polytype, free of sp² carbon, with high structure quality nanocrystals, was realized for the first time by the pyrolysis of organosilane C₁₂H₃₆Si₆ at 8 GPa and temperatures up to 2000 °C. It is shown that the average particle size can be monotonically changed from ~2 nm to ~500 nm by increasing the synthesis temperature from 800 °C to 1400 °C. At higher temperatures, further enlargement of the crystals is impeded, which is consistent with the recrystallization mechanism driven by a decrease in the surface energy of the particles. The optical properties investigated by IR transmission spectroscopy, Raman scattering, and low-temperature photoluminescence provided information about the concentration and distribution of carriers in nanoparticles, as well as the dominant type of internal point defects. It is shown that changing the growth modes in combination with heat treatment enables control over not only the average crystal size, but also the LO phonon—plasmon coupled modes in the crystals, which is of interest for applications related to IR photonics.

Enhancing Spectral Reflection through Controlled Phase Distribution Using Doped Polar-Dielectric Metasurfaces

Controlling the phase distribution of wavefronts using optical metasurfaces has led to interesting optical properties and applications. Here, we explore the control of phase distribution through polar-dielectric metasurfaces composed of doped SiC nanosphere arrays. We investigate the impact of doping concentration on the optical properties of SiC nano-spheres. Our results indicate that increasing the doping of SiC nanoparticles influenced electric dipolar resonances, whereas it did not change the dipolar resonances. Using this concept, we numerically studied the extension of this idea to form metasurface arrays of single, dimer and linear trimers of the doped SiC nano-spheres. Using different doping schemes, we studied the improvement of the reflectivity at frequencies greater than the longitudinal optical phonon frequency.

Longitudinal optical phonon-plasmon coupling in luminescent 3C-SiC nanocrystal films

Glycerol-passivated 3C-SiC nanocrystal (NC) solid films with tunable blue photoluminescence show abnormal longitudinal optical (LO) phonon behavior. As the NC size increases, the LO phonon intensity increases in the Raman spectra of the solid films and is even larger than that of the transverse optical mode. The Raman spectra cannot be fitted by using only the phonon confinement model. When further considering the coupling between the LO phonon and plasmon induced by the surface deformation potential in the glycerol layer, good agreement is achieved between the experiments and theory. This indicates that the coupled LO phonon-plasmon effect arising from the surface bonding structure plays a crucial role in the modified LO phonon behavior.