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Lecture 8 - NP nucleation and growth

Lecture 8 - NP nucleation and growth - MSE 803...

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MSE 803: N ANOMATERIALS AND N ANOTECHNOLOGY Professor Xudong Wang 213 MSE Building Spring 2010 Class 8: Nanoparticle Nucleation and Growth
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G. Cao, Nanostructures & Nanomaterials, Imperial College Press (2003) Synthesis of Nanoparticles Many methods have been investigated for nanoparticle growth Homogenous nucleation Fundamentals of homogeneous nucleation Subsequent growth of nuclei Growth controlled by diffusion Growth controlled by surface process Synthesis of metal nanoparticles Semiconductor nanoparticles Expitaxial Core-Shell Particles Oxide nanoparticles Sol-gel processing, Forced hydrolysis, Controlled release of ions Vapor phase reactions Solid state phase segregation Heterogeneous Nucleation Kinetically Confined Synthesis
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Approaches for Synthesis of Nanoparticles In thermodynamic approach, synthesis consists of: - generation of supersaturation, nucleation and subsequent growth In kinetic approach : NP formation by having a limiting amount of precursors available for growth, such as in MBE, or by confining process to a limited space, such as growth by aerosol or micelle synthesis First consider thermodynamic approach Identical size for all particles Identical shape or morphology Identical chemical composition and crystal structure Produce individually dispersed or monodispersed NP system (no agglomeration) If agglomerated system should be readily dispersible
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Synthesis of Nanoparticles: General Considerations To synthesis nanoparticles by homogenous nucleation must first form a supersaturated solution Can form supersaturated solution by cooling a saturated solution held at equilibrium Can create a supersaturation in situ by converting highly soluble chemical into less soluble chemicals Nanoparticles can be synthesized by homogeneous nucleation in one of three mediums, liquid, gas and solid.
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Fundamentals of Homogenous Nucleation When concentration of solute in a solvent exceeds saturation precipitate a new phase Reduce overall Gibbs free energy of supersaturated solution by forming a solid phase and maintaining an equilibrium concentration in solution Reduction of Gibbs free energy is the driving force for nucleation and growth ) 1 ln( ) / ln( kT C C kT G o v Gibbs free energy of different phases Change in Gibbs fee energy per unit volume of solid phase, Δ G v , is dependent
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