Control and expression of --NH$_{2}$, --SH, --COOH and SiO$_{2}$ on the surface of silicon carbide quantum dots

We present simple protocols for reliably tailoring the surfaces of \textit{zinc blende} silicon carbide quantum dots ($\beta $-SiC QDs). The SiC QDs are synthesized via photo-assisted electrochemical corrosion of bulk powders at different temperatures and time scales. After washing the residual acid and resuspending in H$_{2}$O, the surfaces of SiC QDs were controllably coated with four different functional groups, specifically --NH$_{2}$, --SH, and --COOH and --SiO$_{2}$. We began by covalently attaching primary amines (-NH$_{2})$ to the QD surface. The amine terminations were then converted to amine/thiolate (-NH$_{2}$/SH) and amine/carboxylate (-NH$_{2}$/COOH) functional groups. SiO$_{2}$ shells around SiC QDs (\textit{to create SiC@SiO}$_{2}$\textit{ nano-structures}) were grown using a TEOS-mediated St\"{o}ber method. The presence of amine and thiol groups was confirmed by fluoresceamine assay test, X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR). While a negative fluoresceamine assay test confirmed the replacement of amine groups by thiol groups, the thiolation of the surface was also confirmed through Ellman's assay, XPS and FTIR. The presence of the SiO$_{2}$ shells was examined using transmission electron microscopy and XPS. Our results open up possibilities to manipulate SiC QDs for various applications.