Modeling the Electronic, Structural and Vibrational Properties of Cubic SiC Nanocrystals Built from Diamondoid Structures

Abstract

Silicon carbide diamondoids are used as building blocks of cubic SiC nanocrystals. Density functional theory (DFT) at the generalized gradient approximation level of Perdew, Burke and Ernzerhof (PBE) with 6-31G(d) basis is used to investigate the electronic structure of these diamondoids up to 12 cages. The results show that the energy gap and bond lengths generally decrease with shape fluctuations as the number of atoms increases. Electronic and structural properties are in good agreement with both previous experimental and theoretical results. Vibrational modes converge to the SiC experimental bulk limit of the radial breathing mode while hydrogen related modes are nearly constant in their frequencies. It is suggested in this work to identify SiC-diamondoids from their hydrogen vibrational modes finger print in the range (1000-3000 cm⁻¹) and identify the size of the diamondoid from low frequency vibrational modes (0-1000 cm⁻¹) such as radial breathing modes.