Synthesis of silicon quantum dots using cyclohexasilane (Si6H12)

We report a novel, ambient pressure, continuous gas-phase, synthesis of Si-QDs by direct pyrolysis of cyclohexasilane (CHS, Si6H12), a liquid hydrosilane. We also report that using a low activation energy precursor such as Si6H12 enabled effective gas-phase reduction of the hydrosilane leading to better nucleation of Si nanoparticles than other hydrosilanes. By suitably designing the reactor length and its temperature profile, the structure of the Si-QDs are rendered amorphous or crystalline. The as-synthesized Si-QDs were thermally hydrosilylated with 1-dodecene and their properties examined. High resolution transmission electron microscopic (HRTEM) analysis revealed that the nano-crystalline Si-QDs (Si-NCs) have an average size of 2.0 nm. The amorphous Si-QDs (a-Si-QDs) and the Si-NCs samples exhibited UV-Vis absorptions below 300 and 375 nm, respectively. The a-Si-QDs and Si-NCs excited at 300 nm showed PL emissions at ∼370 nm and 374 nm, respectively, while the latter showed additional characteristic emissions at 403, 425 and 457 nm. The quantum yields were determined to be 9 and 13%, respectively, with PL relaxation life times of 6.5 and 13 ns, respectively.