Effects of surface and confinement on the optical vibrational modes and dielectric function of 3C porous silicon carbide: An ab-initio study

Nanoporous silicon carbide is an interesting material with multiple potential applications, especially in supercapacitors, while there are many experimental investigations on the properties of this material, theoretical studies on its vibrational and optical properties are still scarce. This work studies the effect of quantum confinement on the dielectric function and optical vibrational modes of 3C porous silicon carbide from ab-initio calculations using density functional theory and density functional perturbation theory. The porous structures are modelled in the [001] direction by removing columns of atoms of a perfect Si crystal, obtaining two surface configurations: one with only C atoms and another one with Si atoms. Results show that the optical phonon modes of Si and C undergo a shift towards lower frequencies compared to their bulk counterparts due to phonon confinement effects. However, this shift is masked by H bending vibrations. Also, a surface H exchange process is observed on the Si-rich pore surface due to bond stretching and bending vibrations. The dielectric function analysis shows an increased optical activity in the porous cases due to a shift of the conduction band minimum towards gamma point for the C-rich case and high porosity Si-rich case, owing to quantum confinement effects. These results could be important for the applications of these nanostructures devices such as sensors and UV detectors.