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Chemical
Synthesis
The synthesis of nearly monodisperse collections of well-passivated nanoparticles is essential in order to study the intrinsic effects of particle size and composition on the magnetic and optical properties of these materials. . We currently synthesize a variety of inorganic compounds using solution-phase chemical techniques: Bi, Bi1-xSbx, PbSe, Bi2S3, Co, CoPt and Mn-doped Pb chalcogenides. For our semiconductor and semimetal nanoparticle materials, we use a high-temperature coprecipitation from organometallic precursors. This class of synthesis techniques results in highly-crystalline nanoparticles, passivated with a monolayer of organic molecules. The passivation is required not only to terminate the chemical bonds on the particle's surface, but to also allow the particles to be dissolved and manipulated in solution and precipitated by evaporation of the solvent. The passivation prevents agglomeration and oxidation of the particles. Coupled with a post-synthesis size selection procedure, particles with size variation of less than 5% can be isolated in solution. A variety of different capping ligands can be employed including phosphines, amines and carboxylate acids, and these surface ligands can be changed in post-synthesis procedures. In addition, these particle colloids can be dried and redissolved in various organic solvents, deposited to from close-packed ordered arrays of nanoparticles or incorporated into a polymer matrices. An alternative chemical synthesis method we sometimes use is the reverse micelle technique. Briefly, reverse micelles are nanometer-sized droplets of water encased by a surfactant and suspended in oil. The reverse micelles can be used to synthesize size-controlled inorganic crystallites by carrying out aqueous chemical reactions (coprecipitation or reduction) in the water droplets. The reverse micelles restrict the growth of the particle and prevent aggregation. References |
