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Lecture 4

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chichi's version from 2018-02-26 21:46

Section 1

Question Answer
Synthesis and Characterization of NanomaterialsGas phase methods, homogenous nucleation of particles
Physical Vapor Deposition (PVD)Evaporation-condensation, molecular beam epitaxy (MBE), sputter-deposit
CVDChemical Vapor Deposition
PLDPulsed Laser Deposition
Homogenous nucleation occurs...in the absence of any foreign particles or ions when the vapor molecules condense to form embryonic droplets or nuclei
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Section 2

Question Answer
Basic idea of techniques for cluster and particle formationevaporate a material, then let is condense by bringing it into a supersaturated state. Nucleation theory applies to clusters. Particles are obtained by growing clusters much farther beyond the nucleation point.
Methods of techniques for cluster and partcle formationPhysical cooling of vapor by expansion. Clusters from oven source. Laser vaporization. These methods can be used to produce clusters or particles.
Clusters from oven source (Step 1)Melt then boil a metal to produce vapor at high pressure
Clusters from oven source (Step 2)Mix with inert gas and expand into lower background pressure.
Clusters from oven source (Step 3)The vapor cools and nucleates clusters.
Cluster from oven source (Step 4)Clusters tend to be larger with heavier carrier gas.
Clusters from oven source (Step 5)The technique is less useful for metals with high boiling point
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Section 3

Question Answer
Laser Vaporization (Step 1)High energy pulse of laser with intensity of 107 Wcm^2 focused on a target containing the material to be made into clusters
Laser Vaporization (Step 2)Laser pulse results in high heating rate and vaporiztion of the material at the surface, without heating the entire sample.
_________ start as clusters but grow farther beyond nucleationParticles
In terms of production, particles are generated in _______ amounts.large
Particles are normally characterized after they are___________.collected
Clusters are characterized while in the _________ stage.production
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