Silicon-Carbide Nanocrystals from Nonthermal Plasma: Surface Chemistry and Quantum Confinement

Silicon-carbide (SiC) nanocrystals (NCs) of controlled 2-4 nm size are produced in low-pressure nonthermal plasma from the simple alkylsilane precursor tetramethylsilane (TMS). Generating material on the slightly carbon-rich side of 50/50 Si/ C, we establish a process for thermally removing residual carbon, which in turn promotes a degree of intrinsic solubility in polar solvents such as isopropanol (IPA). Using the size dependent Tauc gap of luminescent silicon NCs (Si NCs) as a point of reference, we demonstrate quantum confinement in nanocrystalline beta-SiC but without measurable luminescence. Surface-sensitive spectroscopic techniques reveal an oxide shell surrounding a nanocrystalline SiC core, where negative surface charge groups promote solubility while likely acting as efficient trap states for nonradiative recombination. An analytical model is presented that combines electrostatic repulsion with van der Waals attraction to explain experimental observations of concentration-dependent cluster formation and reversible NC aggregation. We anticipate that these materials will be of interest for use as nanofillers in polymer composites and in specialty coatings, while providing a foundation for exploring routes to band gap emission from nanocrystalline SiC.