High-Yield Synthesis of Hexagonal Non-Close-Packed Carbon Dots by Electron Irradiation of Polymer Colloidal Crystals

Hexagonal non-close-packed (HNCP) quantum-sized carbon dots with the diameters less than 10 nm were mass-synthesized by electron irradiation of polymer colloidal crystals and subsequent heating. Monolayer colloidal crystals were fabricated by spin-coating of polystyrene (PS) nanospheres with the sizes ranging 100 - 500 nm on Si(100) substrates. The PS colloidal crystals were irradiated with an electron beam of 50 keV at different electron fluences up to 1018 cm-2. The electron-irradiated samples were heated at 300 degree for 3 h in a furnace. The morphology, chemical composition and optical properties of as-prepared samples were characterized by SEM, TEM, UV-Vis, FT-IR and Raman spectrometer. PS spheres were decomposed by the electron irradiation and thus the chemical structure of the PS sphere was slowly converted into a carbonaceous material. Heating process removes polymeric materials in the electron-irradiated PS spheres and consequently each PS sphere were transformed into carbon dots with the sizes of less than 10 nm. As a result, regularly-ordered HNCP arrays of carbon dots were created from the monolayer PS colloidal crystals. The HNCP carbon dots can be widely used for photonic crystals, optoelectronic devices, and imaging of bioactive molecules