Syntheses, surface modifications, and applications of supra quantum dots and magnetic nanoparticles

MasterThis thesis describes synthesis of nanoparticles which have novel electric or magnetic properties and their various applications through proper surface modifications. Nanoparticles have unique characteristics discriminated from bulk materials due to their nanometer scale dimension. Not only composing materials are critical to determine the characteristics of the nanoparticles, but the surface chemistries are also important. Nanoparticles are capped with surface ligands and stabilized in certain solvents. The ligands can be exchanged with other ligands to change solvents or perform additional surface treatments such as shell or film coating, and conjugation with other nanoparticles. Supra quantum dots (SQDs) are sphere nanoparticles that consist of hundreds of quantum dots (QDs) to construct large size three-dimensional self-assemblies. The size of SQDs is much larger than their Bohr radius, but SQDs maintain quantum confinement effect of individual QDs. SQDs were size-tunable and could be synthesized with various cadmium chalcogenide (II-VI) materials. SQDs could be dispersed in various solvents after surface modifications, which made it possible to perform facile solution process to fabricate solar cells. After pyridine exchange, SQD and nanorod solutions were blended and spin-coated onto ITO-patterned glasses and formed active layer films by thermal treatment. CdTe and CdSe nanocrystal solution blending and sequential deposition formed p-n nano-heterojunction structures of active layers. Fabrication of an all-inorganic type solar cell was completed with depositing aluminum electrodes onto the active layer films. The solar cell devices used SQDs with nanorods exhibited better performances compared with nanorod-only structure devices. The best performance device exhibited 3.03% of power conversion efficiency. Iron oxide nanoparticles (IONPs) are nanometer scale chemical compounds composed of iron and oxygen, which have superparamagnetic property. Water dispersed superparamagnetic nanoperticles can be utilized in biomedical applications such as contrast agent for magnetic resonance imaging (MRI) and targeted drug delivery in tumor therapy. Various sizes of IONPs were synthesized in organic solvent by thermal decomposition method, and dispersed in hydrophilic solvents after surface modifications. Catechol or pyrogallol ligands were selected to give binding affinity with iron oxide, and they also contained hydrophilic moiety such as carboxyl group. Original inorganic sizes and hydrodynamic sizes of IONPs were maintained after the ligand exchange with dihydroxyhydrocinnamic acid (DHCA), gallic acid (GA), and tannic acid (TA)