Center for Functional Nanomaterials Seminar

Silicon nanocrystals or quantum dots combine the abundance and nontoxicity of silicon with quantized and size-tunable energy band structure of quantum dots to form a new type of functional material that could find applications in biomedical fluorescence imaging, photodynamic therapy, light-emitting devices, and solar cells. Surface of silicon nanocrystals is a major concern for using them in bio-related applications. Room temperature hydrosilylation is introduced to functionalize silicon nanocrystals in darkness to minimize temperature/photon-induced side reactions which can potentially damage the capping ligands or nanocrystal surface. As a proof of concept, silicon nanocrystals are passivated with styrene at room temperature, without styrene polymerization. Silicon nanocrystals are also conjugated to iron oxide nanocrystals to generate a fluorescent/magnetic cell labeling probe. Thermally-induced thiolation is discovered to generate silicon nanocrystals passivated with silicon-sulfur bonds which are metastable and can be turn to silicon-carbon bonds through ligand exchange. The band gap and emission color of silicon nanocrystals are determined by their sizes. Monodisperse silicon nanocrystals and self-assembly of those nanocrystals are of great importance for their applications in light-emitting devices and solar cells. Silicon nanocrystals are size-selected through a modified size-selective precipitation, in which aggregation and precipitation are allowed to take place simultaneously. Face-centered cubic superlattices are assembled with size-selected silicon nanocrystals, and characterized by grazing incidence small angle X-ray scattering. The structure of silicon nanocrystal superlattice is found to be stable at temperature as high as 375oC. Simple hexagonal AlB2 binary superlattice is also formed with silicon and gold nanocrystals