Synthesis Of Gold Nanocrystals And Their Optical Properties

Inorganic nanocrystals show some unique optical properties, which strongly depend on their dimensions, shapes, interparticle spacings, and the properties of the shell ligands. In particular, gold nanocrystals with unique and flexible chemical and physical properties show promising applications in many fields like nano-biotechnology, catalysts, optics, electronics etc. In chapter 1, the research progress on gold nanocrystals was summarized, including their synthesis, assembly, optical properties and potential applications.Synthesis of the gold nanocrystals from solution chemistry was described in Chapter 2. Gold nanoparticles with various sizes were synthesized by developed methods like Frenz and Brust approaches. Gold nanocrystals with different shapes like rods, cubes etc. were prepared by developed seed-growth method; and new gold crystals were also achieved by employing weak reducing agents to reduce gold ions. In addition, the surface Plasmon resonance properties of the gold nanocrystals were fully studied and summarized. This chapter paved the way for the advanced assembly of gold nanocrystals and for the further study of their properties.Chapter 3 focused on the study of gold atomic clusters and their emission property. By employing biomolecules as etching agents, gold nanocrystals were etched and the gold clusters with a smaller size were produced. The obtained Au clusters were characterized by UV-Vis, photoluminescence, transmission electron microscopy (TEM) and electrospray ionization mass spectroscopy (ESI-MS). The results demonstrated that the smaller products were exclusively composed of gold atomic clusters with 8 atoms ("magic" clusters). The formation mechanism of the Au clusters was also studied and proposed as nitrogen-atom-activated surface reaction. Besides, the photoluminescence properties of the clusters under various chemical conditions were investigated and the results revealed the unique surface properties of the atomic clusters. The facile green-chemistry synthesis approach coupled with the exceptional emission properties, the gold clusters envision applications in many fields like nano-biotechnology, sensors etc.In chapter 4, gold nanocrystals and carbon nanotubes hybrids were in situ fabricated by introducing chemically-bifunctional perylene derivatives as interlinkers. The dimensions of the nanoparticles and their density on the surface of carbon nanotubes can be facilely tuned. The formation mechanism of the hybrids was proposed, and it indicated that the bifunctional perylene derivative played dual functions and could control the nucleation and growth of the gold nanocrystals. The optical properties of the hybrids were also investigated and it showed that the hybrids exhibited strong blue photoluminescence under UV lamp irradiation. This novel property may extend the potential application of the hybrids into wider fields like biological labeling, light-emitting devices etc.In chapter 5, the attention was paid to tailor the shell monolayer of the gold nanoparticles. Well-known phase-transfer reaction for organic synthesis was introduced to functionalize monolayer-protected gold nanoparticles (MPNs). The alkyl chains were successfully bonded to the original monolayers by phase-transfer reaction, which made MPNs become soluble in oil phase and insoluble in water phase. The Langmuir-Blodgett technique was employed to assemble these oil-soluble MPNs into thin films on various substrates. The assembly behaviors of these MPNs were investigated by SEM, TEM and AFM. The surface Plasmon resonance properties of the MPNs films were also studied, and it was found that the SPR was red-shifted largely due to the coupling effect.In summary, this dissertation focuses on the relationship between gold nanocrystals and their optical properties from several perspectives, such as tailoring the intrinsic gold cores (size and shape), functionalizing the outer organic shell layer, hybridizing with other nanomaterials, and assembling into ordered two-dimensional structures etc.